General Description
The MAXQ3180 is a dedicated electricity measurement
front-end that collects and calculates polyphase volt-
age, current, power, energy, and many other metering
and power-quality parameters of a polyphase load. The
computed results can be retrieved by an external mas-
ter through the on-chip serial peripheral interface
(SPI™) bus. This bus is also used by the external mas-
ter to configure the operation of the MAXQ3180 and
monitor the status of operations.
The MAXQ3180 performs voltage and current measure-
ments using an integrated ADC that can measure up to
seven external differential signal pairs. An eighth differ-
ential signal pair is used to measure the die tempera-
ture. An internal amplifier automatically adjusts the
current channel gain to compensate for low-current
channel-signal levels.
Applications
3-Phase Multifunction Electricity Meters
Features
Compatible with 3-Phase/3-Wire, 3-Phase/4-Wire,
and Other 3-Phase Services
Active Power and Energy of Each Phase and
Combined 3-Phase (kWh), Positive and Negative
Reactive Power and Energy of Each Phase and
Combined, Positive and Negative
Apparent Power and Energy of Each Phase and
Combined 3-Phase
Neutral Line Current Measurement
Line Frequency (Hz)
Power Factors
Voltage Phasor Angles
Phase Sequence Indication
Phase Voltage Absence Detection
Voltage and Current Harmonic Measurement
Fundamental and Total Power and Energy
Two Pulse Outputs: Configurable for Active,
Reactive, and Apparent Powers
Programmable Pulse Widths
Programmable No-Load Current Threshold
Programmable Meter Constants
Programmable Thresholds for Undervoltage and
Overvoltage Detection
Programmable Threshold for Overcurrent Detection
Amp-Hours in Absence of Voltage Signals
On-Chip Digital Temperature Sensor
Precision Internal Voltage Reference 2.048V
(30ppm/°C typical), Also Supports An External
Voltage Reference
Supports Software Meter Calibration
Up to 3-Point Multipoint Calibration to
Compensate for Transducer Nonlinearity
Power-Fail Detection
Bidirectional Reset Input/Output
SPI-Compatible Serial Interface with Interrupt
Request (IRQ) Output
Single 3.3V Supply, Low Power (35mW typical)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
________________________________________________________________
Maxim Integrated Products
1
19-4674; Rev 3; 12/09
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device may be
simultaneously available through various sales channels. For information about device errata, go to: www.maxim-ic.com/errata.
MAXQ is a registered trademark of Maxim Integrated Products, Inc.
SPI is a trademark of Motorola, Inc.
Ordering Information
+
Denotes a lead(Pb)-free/RoHS-compliant package.
PART TEMP RANGE PIN-PACKAGE
MAXQ3180-RAN+ -40°C to +85°C 28 TSSOP
Pin Configuration and Typical Application Circuit appear at
end of data sheet.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
2 _______________________________________________________________________________________
Absolute Maximum Ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Metering Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
Electrical Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
SPI Slave Mode Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Pin Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .14
Detailed Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Analog Front-End . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Digital Signal Processor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Precision Pulse Generators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
SPI Peripheral . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Operating Modes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Run Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Stop Mode . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
Reset Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
External Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Power-On Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Watchdog Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Software Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Power-Supply Monitoring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Clock Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
External High-Frequency Crystal . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
External High-Frequency Clock . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Internal RC Oscillator . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
Master Communications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
SPI Communications Rate and Format . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19
SPI Communications Protocol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
Host Software Design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Register Set . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
RAM-Based Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
General Operating Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Global Status Register (STATUS) (0x000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Operating Mode Register 0 (OPMODE0) (0x001) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Operating Mode Register 1 (OPMODE1) (0x002) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Operating Mode Register 2 (OPMODE2) (0x003) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .31
TABLE OF CONTENTS
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
_______________________________________________________________________________________ 3
Global Interrupt Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Interrupt Request Flag Register (IRQ_FLAG) (0x004) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33
Interrupt Mask Register (IRQ_MASK) (0x006) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34
Meter Pulse Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Pulse Configuration—CFP Output (PLSCFG1) (0x01E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Pulse Configuration—CFQ Output (PLSCFG2) (0x01F) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
CFP Pulse Width (PLS1_WD) (0x020) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .36
CFP Pulse Threshold (THR1) (0x022) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
CFQ Pulse Width (PLS2_WD) (0x026) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .37
CFQ Pulse Threshold (THR2) (0x028) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Calibration Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
Current Gain, Phase X = A/B/C/N (X.I_GAIN) (A: 0x130, B: 0x21C, C: 0x308, N: 0x12E) . . . . . . . . . . . . . . . . . . .38
Voltage Gain, Phase X = A/B/C (X.V_GAIN) (A: 0x132, B: 0x21E, C: 0x30A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Energy Gain, Phase X = A/B/C (X.E_GAIN) (A: 0x134, B: 0x220, C: 0x30C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39
Phase-Angle Compensation, High Range, Phase X = A/B/C (X.PA0) (A: 0x13E, B: 0x22A, C: 0x316) . . . . . . . . .39
Phase-Angle Compensation, Medium Range, Phase X = A/B/C (X.PA1) (A: 0x140, B: 0x22C, C: 0x318) . . . . . .40
Phase-Angle Compensation, Low Range, Phase X = A/B/C (X.PA2) (A: 0x142, B: 0x22E, C: 0x31A) . . . . . . . . .40
Limit Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Overcurrent Level (OCLVL) (0x044) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40
Overvoltage Level (OVLVL) (0x046) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Undervoltage Level (UVLVL) (0x048) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
No-Load Level (NOLOAD) (0x04A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .41
Phase Status Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Interrupt Flags, Phase X = A/B/C (X.FLAGS) (A: 0x144, B: 0x230, C: 0x31C) . . . . . . . . . . . . . . . . . . . . . . . . . . . .42
Interrupt Mask, Phase X = A/B/C (X.MASK) (A: 0x145, B: 0x231, C: 0x31D) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .43
Energy Overflow Flags, Phase X = A/B/C (X.EOVER) (A: 0x146, B: 0x232, C: 0x31E) . . . . . . . . . . . . . . . . . . . . .43
Measurements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Line Frequency (LINEFR) (0x062) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
Power Factor, Phase X = A/B/C (X.PF) (A: 0x1C6, B: 0x2B2, C: 0x39E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
RMS Voltage, Phase X = A/B/C (X.VRMS) (A: 0x1C8, B: 0x2B4, C: 0x3A0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44
RMS Current, Phase X = A/B/C (X.IRMS) (A: 0x1CC, B: 0x2B8, C: 0x3A4) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .45
Energy, Real Positive, Phase X = A/B/C (X.EAPOS) (A: 0x1E8, B: 0x2D4, C: 0x3C0) . . . . . . . . . . . . . . . . . . . . . .45
Energy, Real Negative, Phase X = A/B/C (X.EANEG) (A: 0x1EC, B: 0x2D8, C: 0x3C4) . . . . . . . . . . . . . . . . . . . . .46
Energy, Reactive Positive, Phase X = A/B/C (X.ERPOS) (A: 0x1F0, B: 0x2DC, C: 0x3C8) . . . . . . . . . . . . . . . . . .46
Energy, Reactive Negative, Phase X = A/B/C (X.ERNEG) (A: 0x1F4, B: 0x2E0, C: 0x3CC) . . . . . . . . . . . . . . . . .47
Energy, Apparent, Phase X = A/B/C (X.ES) (A: 0x1F8, B: 0x2E4, C: 0x3D0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .47
TABLE OF CONTENTS (continued)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
4 _______________________________________________________________________________________
Virtual Register Conversion Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
Voltage Units Conversion Coefficient (VOLT_CC) (0x014) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
Current Units Conversion Coefficient (AMP_CC) (0x016) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48
Power Units Conversion Coefficient (PWR_CC) (0x018) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49
Energy Units Conversion Coefficient (ENR_CC) (0x01A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50
Virtual Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51
Real Power, Phase X = A/B/C/T (PWRP.X) (A: 0x801, B: 0x802, C: 0x804, T: 0x807) . . . . . . . . . . . . . . . . . . .51
Reactive Power, Phase X = A/B/C/T (PWRQ.X) (A: 0x811, B: 0x812, C: 0x814, T: 0x817) . . . . . . . . . . . . . . .52
Apparent Power, Phase X = A/B/C/T (PWRS.X) (A: 0x821, B: 0x822, C: 0x824, T: 0x827) . . . . . . . . . . . . . . .52
Voltage and Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
RMS Volts, Phase X = A/B/C (V.X) (A: 0x831, B: 0x832, C: 0x834) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
RMS Amps, Phase X = A/B/C/N (I.X) (A: 0x841, B: 0x842, C: 0x844, N: 0x840) . . . . . . . . . . . . . . . . . . . . . . .53
Power Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
Power Factor (PF.T) (0x867) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .53
Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54
Real Energy, Phase A/B/C/T (ENRP.X) (A: 0x8C1, B: 0x8C2, C: 0x8C4, T: 0x8C7) . . . . . . . . . . . . . . . . . . . . .54
Reactive Energy, Phase A/B/C/T (ENRQ.X) (A: 0x8D1, B: 0x8D2, C: 0x8D4, T: 0x8D7) . . . . . . . . . . . . . . . . .54
Apparent Energy, Phase A/B/C/T (ENRS.X) (A: 0x871, B: 0x872, C: 0x874, T: 0x877) . . . . . . . . . . . . . . . . . .54
Theory of Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Analog Front-End Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Digital Signal Processing (DSP) Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Digital Processing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55
Per Sample Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
Per DSP Cycle Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
Energy Accumulation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
No-Zero-Crossing Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
Phase Sequence Status . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
RMS Voltage, RMS Current, and Energy Calculation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
Power Calculation (Active, Reactive, Apparent) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
Energy Accumulation Start Delay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
No-Load Feature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
On Demand Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
RMS Volts, RMS Amps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .60
Power . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
Power Factor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
TABLE OF CONTENTS (continued)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
_______________________________________________________________________________________ 5
Line Frequency . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
Phasor Angles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .61
Meter Pulse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
Generating Pulses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
Meter Constant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
Interrupts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .62
Overvoltage and Overcurrent Detection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63
Meter Units to Real Units Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .63
Units Conversion Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Calibration Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Calibration Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Calibrating Voltage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66
Calibrating Current . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .66
Calibrating Phase Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
Interfacing the MAXQ3180 to External Hardware . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
Connections to the Power Source . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
Sensor Selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
Voltage Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
Voltage-Divider . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .68
Voltage Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Current Sensors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Current Shunt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Current Transformer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Advanced Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Modifying the ADC Operation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69
Fine-Tuning the DSP Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70
Fine-Tuning the Line Frequency Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70
Fundamental Mode Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70
Harmonic Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70
Low-Power Measurement Mode (LOWPM) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71
Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71
Advanced Calibrations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71
Calibrating Current Offset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .71
Calibrating Linearity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
Calibrating Power/Energy Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
Multipoint Phase Offset Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
TABLE OF CONTENTS (continued)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
6 _______________________________________________________________________________________
Advanced Register Configurations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73
Analog Scan Configuration Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .73
Time Slot Assignment—Current Channel X = A/B/C (SCAN_IX) (A: 0x008, B: 0x00C, C: 0x00A) . . . . . . . . . .73
Time Slot Assignment—Voltage Channel X = A/B/C (SCAN_VX) (A: 0x009, B: 0x00D, C: 0x00B) . . . . . . . . .74
Time Slot Assignment—Neutral Current Channel (SCAN_IN) (0x00E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75
Time Slot Assignment—Temperature Channel (SCAN_TE) (0x00F) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76
Neutral Current and Harmonics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77
Auxiliary Channel Configuration (AUX_CFG) (0x010) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77
DSP System Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77
System Clock Frequency (SYS_KHZ) (0x012) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .77
Cycle Count (CYCNT) (0x01C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78
Number of Scan Frames per DSP Cycle (NS) (0x040) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .78
Filter Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79
Line Cycle Noise Rejection Filter (REJ_NS) (0x02C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79
Line Cycle Averaging Filter (AVG_NS) (0x02E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79
Meter Measurement Averaging Filter (AVG_C) (0x030) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
Meter Measurement Highpass Filter (HPF_C) (0x032) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80
Fundamental Filter Feed-Forward Coefficient (B0FUND) (0x034) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81
Fundamental Filter Feedback Coefficient (A1FUND) (0x036) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81
Harmonic Filter Feed-Forward Coefficient (B0HARM) (0x03A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
Harmonic Filter Feedback Coefficient (A1HARM) (0x03C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
Zero-Cross Lowpass Filter (ZC_LPF) (0x05A) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .82
Hardware Mirror Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
ADC Configuration (R_ACFG) (0x04C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
ADC Conversion Rate (R_ADCRATE) (0x04E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83
ADC Settling Time (R_ADCACQ) (0x050) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84
SPI Configuration (R_SPICF) (0x052) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84
Timeouts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
Zero-Crossing Timeout (NZX_TIMO) (0x054) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
Communications Timeout (COM_TIMO) (0x056) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
Energy Accumulation Timeout (ACC_TIMO) (0x058) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .85
Phase-Angle Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Phase Offset Current Threshold 1 (I1THR) (0x05C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Phase Offset Current Threshold 2 (I2THR) (0x05E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Miscellaneous Gain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Neutral Current Gain (N.I_GAIN) (0x12E) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .86
Gain, Fundamental Energy, Phase X = A/B/C (X.EF_GAIN) (A: 0x136, B: 0x222, C: 0x30E) . . . . . . . . . . . . .87
TABLE OF CONTENTS (continued)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
_______________________________________________________________________________________ 7
Linearity Compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87
Linearity Offset, High Range, Phase X = A/B/C (X.OFFS_HI) (A: 0x138, B: 0x224, C: 0x310) . . . . . . . . . . . . .87
Linearity Gain Coefficient, Low Range, Phase X = A/B/C (X.GAIN_LO) (A: 0x13A, B: 0x226, C: 0x312) . . . .87
Linearity Offset, Low Range, Phase X = A/B/C (X.OFFS_LO) (A: 0x13C, B: 0x228, C: 0x314) . . . . . . . . . . . .88
Measurements—RAM Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88
On-Demand RMS Result (N.IRMS) (0x11C) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .88
Fundamental Energy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .89
Fundamental Energy Overflow Flags, Phase X = A/B/C (X.EFOVER) (A: 0x147, B: 0x233, C: 0x31F) . . . . . .89
Energy, Fundamental, Real Positive, Phase X = A/B/C (X.EAFPOS) (A: 0x1FC, B: 0x2E8, C: 0x3D4) . . . . . .89
Energy, Fundamental, Real Negative, Phase X = A/B/C (X.EAFNEG) (A: 0x200, B: 0x2EC, C: 0x3D8) . . . . .90
Energy, Fundamental, Reactive Positive, Phase X = A/B/C (X.ERFPOS) (A: 0x204, B: 0x2F0, C: 0x3DC) . . .90
Energy, Fundamental, Reactive Negative, Phase X = A/B/C (X.ERFNEG) (A: 0x208, B: 0x2F4, C: 0x3E0) . .91
Energy Fundamental, Apparent, Phase X = A/B/C (X.ESF) (A: 0x20C, B: 0x2F8, C: 0x3E4) . . . . . . . . . . . . . .91
Energy Accumulated in the Last DSP Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92
Real Energy, Phase X = A/B/C (X.ACT) (A: 0x1D0, B: 0x2BC, C: 0x3A8) . . . . . . . . . . . . . . . . . . . . . . . . . . . .92
Reactive Energy, Phase X = A/B/C (X.REA) (A: 0x1D4, B: 0x2C0, C: 0x3AC) . . . . . . . . . . . . . . . . . . . . . . . . .92
Apparent Energy, Phase X = A/B/C (X.APP) (A: 0x1D8, B: 0x2C4, C: 0x3B0) . . . . . . . . . . . . . . . . . . . . . . . . .93
Fundamental Energy Accumulated in the Last DSP Cycle . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .93
Fundamental Real Energy, Phase X = A/B/C (X.ACTF) (A: 0x1DC, B: 0x2C8, C: 0x3B4) . . . . . . . . . . . . . . . .93
Fundamental Reactive Energy, Phase X = A/B/C (X.REAF) (A: 0x1E0, B: 0x2CC, C: 0x3B8) . . . . . . . . . . . . .94
Fundamental Apparent Energy, Phase X = A/B/C (X.APPF) (A: 0x1E4, B: 0x2D0, C: 0x3BC) . . . . . . . . . . . .94
Checksum (CHKSUM) (0x060) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .95
Measurements—Virtual Registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96
Fundamental Real Power, Phase A/B/C/T (PWRPF.X) (A: 0x881, B: 0x882, C: 0x884, T: 0x887) . . . . . . . . . . . . .96
Fundamental Reactive Power, Phase A/B/C/T (PWRQF.X) (A: 0x891, B: 0x892, C: 0x894, T: 0x897) . . . . . . . . . .96
Fundamental Apparent Power, Phase A/B/C/T (PWRSF.X) (A: 0x8A1, B: 0x8A2, C: 0x8A4, T: 0x8A7) . . . . . . . . .97
Fundamental Real Energy, Phase A/B/C/T (ENRPF.X) (A: 0x8E1, B: 0x8E2, C: 0x8E4, T: 0x8E7) . . . . . . . . . . . . .97
Fundamental Reactive Energy, Phase A/B/C/T (ENRQF.X) (A: 0x8F1, B: 0x8F2, C: 0x8F4, T: 0x8F7) . . . . . . . . .97
Fundamental Apparent Energy, Phase A/B/C/T (ENRSF.X) (A: 0x8B1, B: 0x8B2, C: 0x8B4, T: 0x8B7) . . . . . . . .97
Phasors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
Phase B Phasor (VBPH: 0x852) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
Phase C Phasor (VCPH: 0x854) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
Harmonics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
RMS Voltage, Harmonic (V.HARM) (0x830) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
RMS Current, Harmonic/Neutral (I.N, I.HARM) (0x840) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
Ratio of Harmonic/Fundamental (HARM_NF) (0x850) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
TABLE OF CONTENTS (continued)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
8 _______________________________________________________________________________________
Special Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
Applications Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
Grounds and Bypassing . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
Specific Design Considerations for MAXQ3180-Based Systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
Additional Documentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
Technical Support . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
Pin Configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
Package Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .99
Typical Application Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100
Revision History . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .101
TABLE OF CONTENTS (continued)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
_______________________________________________________________________________________ 9
Figure 1. External Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Figure 2. Brownout Reset . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
Figure 3. Simplified Clock Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Figure 4a. SPI Interface Timing (CKPHA = 0) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Figure 4b. SPI Interface Timing (CKPHA = 1) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20
Figure 5. Read SPI Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Figure 6. Write SPI Transfer . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
Figure 7. Flowchart for Reading from MAXQ3180 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Figure 8. Flowchart for Writing to MAXQ3180 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .25
Figure 9. Per Sample Operations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .56
Figure 10. Computation of RMS Values . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57
Figure 11. Phase Compensation for Energy Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58
Figure 12. Apparent and Reactive Energy Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59
Figure 13. Sample Voltage Input Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Figure 14. Sample Current Input Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65
Figure 15. Offset Testing Setup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67
Figure 16. Phase Offset vs. Input Current Calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72
Table 1. Command Format for SPI Register Read . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22
Table 2. Command Format for SPI Register Write . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
Table 3. RAM Register Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
Table 4. Virtual Register Map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
Table 5. Meter Unit Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
Table 6. Virtual Register Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64
Table 7. Virtual Registers That Activate Special Commands . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .98
LIST OF FIGURES
LIST OF TABLES
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
10 ______________________________________________________________________________________
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage Range on DVDD Relative to DGND .........-0.3V to +4.0V
Voltage Range on AVDD Relative to AGND..........-0.3V to +4.0V
Voltage Range on AGND Relative to DGND .........-0.3V to +0.3V
Voltage Range on AVDD Relative to DVDD ..........-0.3V to +0.3V
Voltage Range on Any Pin Relative to
DGND except VxP, IxN Pins..............................-0.3V to +4.0V
Voltage Range on VxP, IxN Relative to AGND ......-0.3V to +4.0V
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +150°C
Lead Soldering Temperature .............................Refer to the IPC/
JEDEC J-STD-020 Specification.
PARAMETER CONDITIONS MIN TYP MAX UNITS
Active Energy Linearity Error DR 1000:1 0.1 %
Reactive Energy Linearity Error DR 1000:1 0.2 %
Apparent Energy Linearity Error DR 1000:1 0.5 %
RMS Voltage Linearity Error DR 20:1 0.5 %
DR 500:1 1.0
RMS Current Linearity Error DR 20:1 0.5 %
Line Frequency Error 0.5 %
Power Factor Error 1.0 %
ELECTRICAL CHARACTERISTICS
(VAVDD = VDVDD = VRST to 3.6V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
POWER-SUPPLY SPECIFICATIONS
Digital Supply Voltage VDVDD V
RST 3.6 V
Power-Fail Interrupt Trip Point VPFW Active mode, EPWRF = 1 2.84 3.13 V
Power-Fail Reset Trip Point VRST Active mode 2.70 2.99 V
Analog Supply Voltage VAVDD V
RST 3.6 V
Analog Supply Current IAVDD f
CLK = 8MHz 0.9 1.8 mA
Digital Supply Current IDVDD f
CLK = 8MHz 8.5 13 mA
Low-Power Measurement Mode
Current ILOWPM LOWPM = 1 (Note 1) 4.2 mA
Stop-Mode Current 0.2 12 μA
DIGITAL I/O SPECIFICATIONS
Input High Voltage VIH 0.7 x
VDVDD V
Input Low Voltage VIL 0.3 x
VDVDD V
Input Hysteresis VIHYS V
DVDD = 3.3V 500 mV
Input Leakage IL V
IN = DGND or VDVDD, pullup off ±0.01 ±1 μA
METERING SPECIFICATIONS
(VAVDD = VDVDD = VRST to 3.6V, Current Channel Dynamic Range 1000:1 at TA= +25°C, unless otherwise noted.) (Note 1)
ABSOLUTE MAXIMUM RATINGS
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 11
ELECTRICAL CHARACTERISTICS (continued)
(VAVDD = VDVDD = VRST to 3.6V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Input Low Current IIL V
IN = 0.4V, weak pullup on -50 μA
RESET Pullup Resistance RRESET 50 150 200 k
IOH = -4mA VDVDD
- 0.4
Output High Voltage (Except
RESET)VOH
IOH = -6mA VDVDD
- 0.5
V
IOL = 4mA 0.4
Output Low Voltage VOL IOL = 6mA 0.5 V
SYSTEM CLOCK SOURCES
External Clock Input Frequency 0 8.12 MHz
External Clock Input Duty Cycle 45 55 %
External HF Crystal Frequency fSYS Fundamental mode 8.12 MHz
XTAL1, XTAL2 Internal Load
Capacitance 16 pF
Internal RC Oscillator Frequency 7.4 7.6 8.6 MHz
Internal RC Oscillator Accuracy ±2 %
Internal RC Oscillator Current 50 120 μA
Internal RC Oscillator Startup
Delay (Note 1) 0.45 μs
ANALOG-TO-DIGITAL CONVERTER
Input Voltage Range 0 VREF V
Common-Mode Bias VCOMM 1.14 V
Offset Error ±2 mV
Offset Error Drift ±8 μV/°C
Gain Error (G = 1) 0.05 %
Spurious-Free Dynamic Range SFDR 90 dB
Total Harmonic Distortion THD 90 dB
Input Bandwidth (-3dB) (Note 1) 7 kHz
INTERNAL VOLTAGE REFERENCE
Temperature Coefficient (Note 1) 30 ppm/°C
Output Voltage VREF 2.048 V
INTERNAL TEMPERATURE SENSOR
Temperature Error (Note 1) -4 +4 °C
SPI SLAVE-MODE INTERFACE TIMING
Maximum SPI Clock Rate fSYS/4 MHz
SCLK Input Pulse-Width High tSCH (Note 3) 4 x
tSYS ns
SCLK Input Pulse-Width Low tSCL (Note 3) 4 x
tSYS ns
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
12 ______________________________________________________________________________________
ELECTRICAL CHARACTERISTICS (continued)
(VAVDD = VDVDD = VRST to 3.6V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SSEL Low to First SCLK Edge
(Slave Enable) tSE (Note 3) 4tSYS ns
Last SCLK Edge to SSEL High
(Slave Disable) tSD tSYS +
5 ns
MOSI Valid to SCLK Sample
Edge (MOSI Setup) tSIS 5 ns
SCLK Sample Edge to MOSI
Change (MOSI Hold) tSIH tSYS +
5 ns
SCLK Shift Edge to MISO Valid
(MISO Hold) tSOV 3tSYS
+ 5 ns
Note 1: Specifications guaranteed by design but not production tested.
Note 2: Specifications to -40°C are guaranteed by design and are not production tested.
Note 3: tSYS = 1/fSYS.
SPI Slave Mode Timing
SSEL SHIFT EDGE SAMPLE EDGE
SCLK
DATA OUTPUT
DATA INPUT
tSD
tSE
tSOV
tSIS tSIH
tSCL tSCH
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 13
Block Diagram
MAXQ3180
CFP, CFQ
COUNTERS I/O
BUFFERS
I/O
REGISTERS
ADC
CFQ
CFP
V2P
I0P
V0P
VCOMM
RESET
VREF
V1P
I1P
I2P
INP
SPI I/O
BUFFERS
I/O
REGISTERS
WATCHDOG
TIMER
ADC CLOCK
PRESCALER
MISO
MOSI
SCLK
SSEL
XTAL1
SYSCLK
ADCCLK XTAL2
I/O
BUFFERS
I/O
REGISTERS
HF RC
OSC/8
HF
XTAL
OSC
POR/
BROWNOUT
MONITOR
16 x 16
HW MULTIPLY
48-BIT ACCUMULATE
IRQ
I2N
VN
I0N
I1N
TEMP
SENSE
REF
ADC CONTROL,
ELECTRICITY
METERING DSP,
COMMUNICATIONS
MANAGER
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
14 ______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
POWER PINS
17, 22 DVDD Digital Supply Voltage
25 AVDD Analog Supply Voltage
18 DGND Digital Ground
9 AGND Analog Ground
23 VCOMM
Voltage Bias. This pin can be used to create an input common-mode DC offset for ADC channel
conversions.
24 VREF
Voltage Reference. Reference voltage for the ADC. An external reference voltage can be connected to
this pin when extremely high accuracy is required.
VOLTAGE AND CURRENT PINS
26, 3, 4 V0P, I0P,
I0N Phase A Voltage and Current Analog Inputs
27, 5, 6 V1P, I1P,
I1N Phase B Voltage and Current Analog Inputs
28, 7, 8 V2P, I2P,
I2N Phase C Voltage and Current Analog Inputs
1 VN Analog Input for Common Voltage
2 INP Analog Input for Neutral Current
CLOCK PINS
10 XTAL2
11 XTAL1
High-Frequency Crystal Input/Output. When using an external high-frequency crystal, the crystal
oscillator circuit should be connected between XTAL1 and XTAL2. When using an externally driven
clock (EXTCLK = 1), the clock should be input at XTAL1, with XTAL2 left unconnected.
12 IRQ Interrupt Request Output. This line is driven low by the device to indicate to the master that an
unmasked interrupt has occurred.
13 SSEL Slave Select Input. This line is the active-low slave select input for the SPI interface.
14 SCLK Slave Clock Input. This line is the clock input for the SPI interface.
15 MOSI
Master Out-Slave In Input. This line is used by the master to transmit data to the slave (the
MAXQ3180) over the SPI interface.
16 MISO
Master In-Slave Out Output. This line is used by the MAXQ3180 (the slave) to transmit data back to
the master over the SPI interface.
19 CFP Pulse Output 1. Configurable to represent energy or RMS voltage or current.
20 CFQ Pulse Output 2. Configurable to represent energy or RMS voltage or current.
21 RESET
Active-Low Reset Input/Output. An external master can reset the MAXQ3180 by driving this pin low.
This pin includes a weak pullup resistor to allow for a combination of wired-OR external reset
sources. An RC circuit is not required for power-up, as this function is provided internally. This pin
also acts as a reset output when the source of the reset is internal to the device (power-fail, watchdog
reset, etc.). In this case, the RESET pin is held low by the device until it exits the reset state, then the
RESET pin is released.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 15
Detailed Description
The MAXQ3180 contains four major subsections: the
analog front-end, the digital signal processor, the preci-
sion pulse generators, and an SPI peripheral for com-
munication to the host processor.
Analog Front-End
The analog front-end (AFE) is an 8-channel analog-to-
digital converter (ADC). It operates autonomously in the
standard configuration, assigning three channels to
phase A, B, and C voltage; three channels to phase A,
B, and C current; one channel to neutral current; and
the last channel to a temperature sensor.
Each channel also contains a programmable-gain
amplifier capable of providing a gain of 1, 2, 4, 8, 16, or
32 incoming signals. Only the voltage channels permit
gain scaling by the host processor. The MAXQ3180
DSP firmware automatically sets the gain on current
channels.
Digital Signal Processor
The DSP code is permanently embedded in masked
ROM and accepts raw current and voltage samples for
each of three phases and continuously calculates a
host of values including RMS volts, RMS amps, real
energy, reactive energy, apparent energy, fundamental
and harmonic energy, and power factor.
The MAXQ3180 DSP core processes incoming sam-
ples from the analog front-end according to user con-
figurations. The host sets these operating parameters
by specifying addresses within the device RAM space.
When a calculation cycle is complete, the results are
placed back into RAM as well. Thus, the DSP core uses
the RAM block as both its input (for operating parame-
ters) and output (for calculation results) medium. See
the
SPI Peripheral
section for how the host writes oper-
ating parameters and reads results from the RAM.
The DSP also calculates certain values such as line fre-
quency and active and reactive powers only when
demanded by the host.
Precision Pulse Generators
The MAXQ3180 includes two precision pulse genera-
tors that generate a pulse whenever certain conditions
are met. In the MAXQ3180, many meter quantities can
be selected for conversion to meter pulses including
absolute energy, net energy, reactive energy, voltage,
and current.
The pulse generators are accumulators. On each DSP
cycle, whatever quantity is being measured—real ener-
gy, reactive energy, current, or something else—is
added to the pulse accumulator. The pulse accumula-
tor is then tested to determine if the value in the accu-
mulator is greater than the threshold. If it is greater, the
threshold value is subtracted from the accumulator
value and the meter pulse starts.
SPI Peripheral
The SPI controller is a slave-only device that can read
or write any location in the data RAM. Additionally, it
can request data from on-demand registers.
The MAXQ3180 implements a truly full-duplex commu-
nication, rather than the pseudo half-duplex mode used
by other SPI peripherals. That is, each time a character
is received by the MAXQ3180, a meaningful character
is returned to the host. Often, this is a protocol charac-
ter. In this way, the host can be assured that the com-
mand has been received and is valid. Optional error
checking can also be enabled to further guarantee
proper operation.
Operating Modes
The MAXQ3180 has two basic modes of operation,
each of which is described in the following sections.
The Initialization Mode is the default mode upon power-
up or following reset; entry to and exit from the other
operating modes is only performed as a result of com-
mands sent by the master.
Run Mode
This mode is the normal operating mode for the
MAXQ3180. In this mode, the MAXQ3180 continuously
executes the following operations:
Scans analog front-end channels and collects raw
voltage and current samples.
Processes voltage and current samples through DSP
filters as enabled and configured.
Calculates power, energy, and other required quanti-
ties and stores these values in RAM registers.
Responds to register write and read commands from
the master.
Outputs power pulses on CFP and CFQ as configured.
Drives IRQ when an interrupt condition has been
detected and the interrupt is not masked.
Stop Mode
This mode places the MAXQ3180 into a power-saving
state where it consumes the least possible amount of
current. In Stop Mode, all functions are suspended,
including the ADC and power and voltage measurement
and processing. The MAXQ3180 does not respond to
any commands from the master in this operating state.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
16 ______________________________________________________________________________________
Entry into Stop Mode only occurs at the request of the
master. To place the MAXQ3180 into Stop Mode, the
master must read the ENTER STOP (0xC02) register.
Once this register has been read, the MAXQ3180
enters Stop Mode immediately, before the transmission
of the final ACK byte by the MAXQ3180.
There are three possible ways to bring the MAXQ3180
back out of Stop Mode.
Power Cycle. The MAXQ3180 automatically exits
Stop Mode if a power-on reset occurs. Following exit
from Stop Mode, all registers are cleared back to
their default states, and the MAXQ3180 transitions to
Initialization Mode.
External Reset. The MAXQ3180 exits Stop Mode if
an external reset is triggered by driving RESET low.
Once the RESET pin is released and allowed to
return to a high state, the MAXQ3180 comes out of
reset and goes into Initialization Mode. All registers
are cleared to their default states when exiting Stop
Mode in this manner.
External Interrupt. Driving the SSEL pin low causes
the MAXQ3180 to exit Stop Mode without undergoing
a reset cycle. When exiting Stop Mode in this man-
ner, all register and configuration settings are
retained, and the MAXQ3180 automatically resumes
electric-metering functions and sample processing.
Note that when the master is communicating with the
MAXQ3180, the SSEL line is normally driven low at the
beginning of each SPI command. This means that if the
master sends an SPI command after the MAXQ3180
enters Stop Mode, the MAXQ3180 automatically exits
Stop Mode.
Reset Sources
There are several different sources that can cause the
MAXQ3180 to undergo a reset cycle. For any type of
hardware reset, the RESET pin is driven low when a
reset occurs.
External Reset
This hardware reset is initiated by an external source
(such as the master controller or a manual pushbutton
press) driving the RESET pin on the MAXQ3180 low.
The RESET line must be held low for at least four cycles
of the currently selected clock for the external reset to
take effect. Once the external reset takes effect, it
remains in effect indefinitely as long as RESET is held
low. Once the external reset has been released, the
MAXQ3180 clears all registers to their default states
and resumes execution in Initialization Mode.
When an external reset occurs outside of Stop Mode,
execution (in Initialization Mode) resumes after four
cycles of the currently selected clock (external high-fre-
quency crystal for Run Mode, 1MHz internal RC oscilla-
tor for LOWPM Mode). As the MAXQ3180 enters
Initialization Mode, the LOWPM bit is always cleared
CLOCK
RESET
RESET
SAMPLING
INTERNAL
RESET
BEGIN RUNNING IN INITIALIZATION MODE
Figure 1. External Reset
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 17
tPOR
VRST1
BROWNOUT DETECTION
BROWNOUT DETECTION (ALWAYS
ENABLED OUTSIDE OF STOP MODE)
FORCES RESET STATE. POR = 1
BROWNOUT DETECTION DISABLED
DURING STOP MODE.
NO RESET IS GENERATED.
BROWNOUT DETECTION DISABLED.
POR LEVEL CAUSES RESET.
VPOR
INTERNAL
RESET
STOP MODE
Figure 2. Brownout Reset
to 0, meaning that the MAXQ3180 always switches to
the high-frequency clock before it begins accepting
commands in Initialization Mode.
When an external reset occurs from Stop Mode, execu-
tion (in Initialization Mode) resumes after 128 cycles of
the internal RC oscillator (or approximately 128μs).
Power-On Reset
When the MAXQ3180 is first powered up, or when the
power supply, VDVDD, drops below the VRST power-fail
trip point (outside of Stop Mode), the MAXQ3180 is
held in power-on reset. Once the power supply rises
above the VRST level, the power-on reset state is
released and all registers are reset to their defaults and
execution resumes in Initialization Mode. The high-fre-
quency external crystal (LOWPM = 0) is always select-
ed as the clock source following any power-on or
brownout reset.
In Stop Mode brownout detection is disabled, so a
power-on reset does not occur until VDVDD drops to a
lower level (VPOR). From the master’s perspective,
power-on resets and brownout resets both cause the
MAXQ3180 to reset in the same way.
Watchdog Reset
The MAXQ3180 includes a hardware watchdog timer that
is armed and periodically reset automatically during nor-
mal operation. Under normal circumstances, the
MAXQ3180 always resets the watchdog timer often
enough to prevent it from expiring. However, if an internal
error of some kind causes the MAXQ3180 to lock up or
enter an endless execution loop, the watchdog timer
expires and triggers an automatic hardware reset. There
is no register flag to indicate to the master that a watch-
dog reset has occurred, but the RESET line strobes low
briefly.
The watchdog timer does not run during Stop Mode.
Software Reset
The master initiates a software reset by setting the
SWRES (OPMODE0.3) bit to 1. When a software reset
occurs, the MAXQ3180 clears all registers to their
default states and returns to Initialization Mode, in the
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
18 ______________________________________________________________________________________
same manner as if an external reset had taken place.
Unlike a hardware reset, however, a software reset does
not cause the MAXQ3180 to drive the RESET line low.
Power-Supply Monitoring
In addition to the hardware reset provided by the
power-on reset and brownout reset circuits, the
MAXQ3180 includes the capability to detect a low
power supply on the DVDD pin and alert the master
through the interrupt (IRQ) mechanism before a hard-
ware reset occurs. This function, which is always
enabled outside of Stop Mode, causes the RAM status
register flag PWRF (IRQ_FLAG.0) to be set to 1 when-
ever VDVDD drops below the VPFW trip point. Once
PWRF has been set to 1 by hardware, it can only be
cleared by the master (or by a system reset). Whenever
PWRF = 1, if the EPWRF interrupt masking bit is also
set to 1, the MAXQ3180 drives IRQ low to signal to the
master that an interrupt condition (in this case, a power-
fail warning) exists and requires attention.
Clock Sources
All operations including ADC sampling and SPI com-
munications are synchronized to a single system clock.
This clock can be obtained from any one of three selec-
table sources, as shown in Figure 3.
External High-Frequency Crystal
The default system clock source for the MAXQ3180 is
an external high-frequency crystal oscillator circuit con-
nected between XTAL1 and XTAL2. When clocked with
an external crystal, a parallel-resonant, AT-cut crystal
oscillating in the fundamental mode is required.
When using a high-frequency crystal, the fundamental
oscillation mode of the crystal operates as inductive
reactance in parallel resonance with external capaci-
tors C1 and C2. The typical values of these external
capacitors vary with the type of crystal being used and
should be selected based on the load capacitance as
suggested by the crystal manufacturer.
Since noise at XTAL1 and XTAL2 can adversely affect
device timing, the crystal and capacitors should always
be placed as close as possible to the XTAL1 and
XTAL2 pins, with connection traces between the crystal
and the device kept as short and direct as possible. In
multiple layer boards, avoid running other high-speed
digital signals underneath the crystal oscillator circuit if
possible, as this could inject unwanted noise into the
clock circuit.
Following power-up or any system reset, the high-fre-
quency clock is automatically selected as the system
clock source. However, before this clock can be used
XTAL IN
RING IN
SYSTEM CLOCK
EXTCLK
STOPM
POR
CLK
ENABLE WATCHDOG RESETRING COUNT
INT/EXT
CRYSTAL
STARTUP TIMER
WATCHDOG TIMER
1MHz
INTERNAL
OSCILLATOR
HF
CRYSTAL
GLITCH-FREE
MUX
ENABLE
CLOCK
GENERATION
Figure 3. Simplified Clock Sources
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 19
for system execution, a crystal warmup timer must
count 65,536 cycles of the high-frequency clock. While
this warmup time period is in effect, execution contin-
ues using the internal 1MHz oscillator. Once the
65,536-cycle count completes (which requires approxi-
mately 8.2ms at 8MHz), the device automatically
switches over to the high-frequency clock. This crystal
warmup timer is also activated upon exit from Stop
Mode, since the high-frequency crystal oscillator is shut
down during Stop Mode.
External High-Frequency Clock
Instead of using a crystal oscillator to generate the
high-frequency clock, it is also possible to input a high-
frequency clock that has been generated by another
source (such as a digital oscillator IC) directly into the
XTAL1 pin of the MAXQ3180.
To use an external high-frequency clock as the system
clock source, the XTAL1 pin should be used as the
clock input and the XTAL2 pin should be left uncon-
nected. The master should also shut down the internal
crystal oscillator circuit by setting the EXTCLK bit
(OPMODE0.4) to 1. This bit is only cleared by the
MAXQ3180 if a power-on or brownout reset occurs and
is unaffected by other resets.
When using an external high-frequency clock, the clock
signal should be generated by a CMOS driver. If the
clock driver is a TTL gate, its output must be connected
to DVDD through a pullup resistor to ensure that the
correct logic levels are generated. To minimize system
noise in the clock circuitry, the external clock source
must meet the maximum rise and fall times and the
minimum high and low times specified for the clock
source in the
Electrical Characteristics
table.
Internal RC Oscillator
When the external high-frequency crystal is warming
up, or when the MAXQ3180 is placed into LOWPM
mode, the system clock is sourced from an internal RC
oscillator. This internal oscillator is designed to provide
the system approximately 1MHz, although the exact
frequency varies over temperature and supply voltage.
If no external crystal circuit or high-frequency clock will
be used, the MAXQ3180 can be forced to operate infi-
nitely from the internal oscillator by grounding XTAL1.
This ensures that the crystal warmup count never com-
pletes, so the MAXQ3180 runs from the internal oscilla-
tor in all active modes.
Master Communications
Before the MAXQ3180 can begin performing electric-
metering operations, the master must initialize a num-
ber of configuration parameters. Since the MAXQ3180
does not contain internal nonvolatile memory, these
parameters (stored in internal registers) must be set by
the master each time a power-up or reset cycle occurs,
or each time a switch is made between LOWPM Mode
and Run Mode.
The external master communicates with the MAXQ3180
over a standard SPI bus, using commands to read and
write values to internal registers on the MAXQ3180.
These registers include, among many other items:
Operating mode settings (Stop Mode, LOWPM
Mode, external clock mode, etc.)
Status and interrupt flags (power-supply failure, over-
current/overvoltage detection, etc.)
Masking control for interrupts to determine which
conditions cause IRQ to be driven low
Configuration settings for analog channel scanning
Power pulse output configuration
Filter coefficients and configuration
Read-only registers containing accumulated power
and energy data
As the MAXQ3180 obtains voltage and current mea-
surements in Run Mode or LOWPM Mode, it accumu-
lates, filters, and performs a number of calculations on
the collected data. Many of these operations (including
the various filtering stages) are configured by settings
in registers written by the master. The output results
can then be read by the master from various read-only
registers in parallel with the ongoing measurement and
processing operations.
SPI Communications Rate and Format
The SPI is an interdevice bus protocol that provides
fast, synchronous, full-duplex communications between
a designated master device and one or more slave
devices. In a MAXQ3180-based design, the
MAXQ3180 would be the slave device connected to a
designated master microcontroller.
The external master initiates all communications trans-
fers. The interrupt request line IRQ, while not technical-
ly part of the SPI bus interface, is also used for
master/slave communications because it allows the
MAXQ3180 to notify the master that an interrupt condi-
tion exists. Some SPI peripherals sacrifice speed in
favor of simulating a half-duplex operation. This is not
the case with the MAXQ3180; it is truly a full-duplex SPI
slave.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
20 ______________________________________________________________________________________
During an SPI transfer, data is simultaneously transmit-
ted and received over two serial data lines (MISO and
MOSI) with respect to a single serial shift clock (SCLK).
The polarity and phase of the serial shift clock are the
primary components in defining the SPI data transfer
format. The polarity of the serial clock corresponds to
the idle logic state of the clock line and, therefore, also
defines which clock edge is the active edge. To define
a serial shift clock signal that idles in a logic-low state
(active clock edge = rising), the clock polarity select
(CKPOL; R_SPICF.0) bit should be configured to a 0,
while setting CKPOL = 1 causes the shift clock to idle in
a logic-high state (active clock edge = falling). The
phase of the serial clock selects which edge is used to
sample the serial shift data. The clock phase select
(CKPHA; R_SPICF.1) bit controls whether the active or
inactive clock edge is used to latch the data. When
CKPHA is set to a logic 1, data is sampled on the inac-
tive clock edge (clock returning to the idle state). When
CKPHA is set to a logic 0, data is sampled on the active
clock edge (clock transition to the active state).
Together, the CKPOL and CKPHA bits allow four possi-
ble SPI data transfer formats.
Transfers over the SPI interface always start with the
most significant bit and end with the least significant
bit. All SPI data transfers to and from the MAXQ3180
are always 8 bits (one byte) in length. The MAXQ3180
SPI interface does not support 16-bit character lengths.
The default format (upon power-up or system reset) for
the MAXQ3180 SPI interface is represented in
Figure 4a (CKPOL = 0; CKPHA = 0). In this format, the
SCLK CYCLE #
(FOR REFERENCE)
SCLK (CKPOL = 0)
SCLK (CKPOL = 1)
MOSI
(FROM MASTER)
MISO
(FROM SLAVE)
SSEL (TO SLAVE)
1
MSB 6 5 4 3 2 1 LSB
2345678
6MSB
*NOT DEFINED BUT NORMALLY MSB OF CHARACTER JUST RECEIVED.
5 4 3 2 1 LSB *
1
MSB 6 5 4 3 2 1 LSB
2345678
MSB*
*NOT DEFINED BUT NORMALLY LSB OF PREVIOUSLY TRANSMITTED CHARACTER.
6 5 4 3 2 1 LSB
SCLK CYCLE #
(FOR REFERENCE)
SCLK (CKPOL = 0)
SCLK (CKPOL = 1)
MOSI
(FROM MASTER)
MISO
(FROM SLAVE)
SSEL (TO SLAVE)
Figure 4b. SPI Interface Timing (CKPHA = 1)
Figure 4a. SPI Interface Timing (CKPHA = 0)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 21
SPI clock idle state is low, and data is shifted in and out
on the rising edge of SCLK. Once SPI communication
with the MAXQ3180 has been established, it is possible
to alter the CKPOL and CKPHA format settings (as well
as changing the SSEL signal from active low to active
high) if desired by writing to the R_SPICF mirror register
and then reading from the special command register
UPD_SFR to copy the R_SPICF value into the internal
SPI configuration register.
Whenever the active clock edge is used for sampling
(CKPHA = 0), the transfer cycle must be started with
assertion of the SSEL signal. This requirement means
that the SSEL signal be deasserted and reasserted
between successive transfers. Conversely, when the
inactive edge is used for sampling (CKPHA = 1), the
SSEL signal may remain low through successive
transfers, allowing the active clock edge to signal the
start of a new transfer.
The clock rate used for the SPI interface is determined
by the bus master, since the MAXQ3180 always oper-
ates as an SPI slave device. However, the maximum
clock rate is limited by the system clock frequency of
the MAXQ3180. For proper communications operation,
the SPI clock frequency used by the master must be
less than or equal to the MAXQ3180’s clock frequency
divided by 4. For example, when the MAXQ3180 is run-
ning at 8MHz, the SPI clock frequency must be 2MHz
or less. And if the MAXQ3180 is running in LOWPM
Mode (or if the crystal is still warming up), the SPI clock
frequency must remain at 250kHz or less for proper
communications operation.
In addition to limiting the overall SPI bus clock rate, the
master must also include a communications delay fol-
lowing each byte transmit/receive cycle. This delay,
which provides the MAXQ3180 with time to process an
ADC sample, should be a minimum of 400 system
clocks. With default settings and running at 8MHz, this
delay time is 50μs. Reducing the system clock frequen-
cy to 1MHz (LOWPM mode) would increase this delay
period by a factor of 8 to 400μs.
SPI Communications Protocol
All transactions between the master and the
MAXQ3180 consist of the master writing to or reading
from one of the MAXQ3180’s registers. To the host, the
MAXQ3180 looks like a memory array that consists of
both RAM and ROM. This is because the ROM firmware
in the MAXQ3180 reads its operational parameters from
RAM and places its results in RAM. Consequently, con-
figuring a MAXQ3180 is as simple as performing a
block write to its RAM locations.
Some read-only memory locations in the MAXQ3180
trigger actions within the device to calculate electricity-
metering results on the fly. The specific function and
purpose of RAM and virtual ROM locations are given in
the register map. There are several different categories
of internal registers on the MAXQ3180.
RAM Registers. The values of these registers are
stored in the internal RAM of the MAXQ3180. Some
can be read and written by the master, while others
are read-only. RAM registers are either 2 or 4 bytes
long (16 or 32 bits), although in some registers not all
the bits have defined values. Read/write registers are
generally either status/flag registers (which can be
written by either the MAXQ3180 or the master), con-
figuration registers (which are written by the master
and read by the MAXQ3180 firmware), or data regis-
ters (which are read-only and are written by the
MAXQ3180 firmware and read by the master).
Virtual Registers. These read-only registers are not
stored in RAM; instead, they contain values that are
calculated on the fly by the MAXQ3180 firmware
when the master reads them. These registers are
used by the master to obtain values such as phase
A, B, and C active, reactive, and apparent power;
power factor; and RMS voltage and current, which
are calculated from currently collected data on an
as-needed basis. Most virtual registers are 8 bytes in
length.
Hardware Registers. These registers control core
functions of the MAXQ3180 including the ADC and
the SPI slave bus controller. Each of these registers
(R_ACFG, R_ADCRATE, R_ADCACQ, R_SPICF, and
OPMODE0 (bit 4, EXTCLK only)) has a register loca-
tion in RAM that “shadows” the value of the hardware
register. To read from a hardware register, the mas-
ter must first read from the special command register
UPD_MIR (A00h) to copy the values from the hard-
ware registers to the mirror registers in RAM, and
then the mirror register in RAM can be read. To write
to a hardware register, the master reverses the
process by writing to the mirror RAM register and
then reading from the special command register
UPD_SFR (900h) to copy the values from the mirror
registers to the hardware registers.
Special Command Registers. These registers
(UPD_SFR and UPD_MIR) do not return meaningful
data when read but instead trigger an operation.
Reading UPD_SFR causes values to be copied from
the mirror registers to hardware, and reading
UPD_MIR causes values to be copied from the hard-
ware to mirror registers.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
22 ______________________________________________________________________________________
Every defined register on the MAXQ3180 has a 12-bit
address (from 0 to 4095). This address is used when
addressing the register for either a read or write opera-
tion. Addresses 0 to 1023 (000h to 3FFh) are used to
address RAM registers. Registers with addresses from
1024 to 4095 (400h to FFFh) are used for virtual regis-
ters and special command registers.
Each command consists of a read/write command
code, a data length (1, 2, 4, or 8 bytes), a 12-bit regis-
ter address, and the specified number of data bytes fol-
lowed optionally by a cyclic redundancy check (CRC).
Since SPI is a full-duplex interface, the master and
slave must both transmit the same number of bytes dur-
ing the command. When a multiple-byte register is read
or written (2/4/8 byte length), the least significant byte is
read or written first in the command.
Every transaction begins with the master sending 2
bytes that contain the command (read or write), the
address to access, and the number of bytes to transfer.
Every SPI peripheral must return 1 byte for every byte it
receives. If the master is reading 1 or more bytes from
the MAXQ3180, it must send dummy bytes during the
cycles when it is receiving a multibyte response to a
request, meeting the “send a byte to get a byte” require-
ment. But the MAXQ3180 could require time to calculate
the result, and thus might not have it ready when the
master sends the dummy byte. For this reason, the
MAXQ3180 always sends zero or more bytes of a NAK
character (0x4E or ASCII ‘N’) followed by an ACK char-
acter (0x41, or ASCII ‘A’) before sending the data.
If the master is writing 1 or more bytes, it sends the
data to be written immediately after sending the com-
mand. The MAXQ3180 returns ACK (0x41) for each
data byte. It then returns NAK (0x4E) until the write
cycle is complete, after which it returns a final ACK.
Immediately after the final ACK, the MAXQ3180 is
ready to begin the next transaction; there is no need to
wait for any other event. It is not even necessary to tog-
gle SSEL to begin the next transaction. The MAXQ3180
knows that the first transaction is over and is ready for
the next.
If, for whatever reason, it is necessary to reset the com-
munications between the host and the MAXQ3180 (for
Table 1. Command Format for SPI Register Read
BYTE TRANSFERS BIT DESCRIPTION
7:6
Command Code:
00 Read
01 Reserved
10 Write
11 Reserved
5:4
Data Length:
00 1 Byte
01 2 Bytes
10 4 Bytes
11 8 Bytes
1st byte Master sends command;
Slave sends 0xC1 byte
3:0 MSB portion of data address.
2nd byte Master sends address;
Slave sends 0xC2 byte 7:0 LSB portion of data address.
Sync bytes
Master sends dummy;
Slave sends ACK (0x41) or
NACK (0x4E) byte
7:0
Master sends dummy byte; Slave responds with NACK if busy,
or with ACK when processing complete.
Master must receive ACK, then receive data.
3rd byte
(1st data byte)
Master sends dummy;
Slave sends data 7:0 Data, LSB
... ... ... ...
Nth byte
(Last data byte)
Master sends dummy;
Slave sends data 7:0 Data, MSB
(N + 1) byte Master sends dummy;
Slave sends CRC 7:0 Optional CRC
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 23
Table 2. Command Format for SPI Register Write
BYTE TRANSFERS BIT DESCRIPTION
7:6
Command code:
00 Read
01 Reserved
10 Write
11 Reserved
5:4
Data Length:
00 1 Byte
01 2 Bytes
10 4 Bytes
11 8 Bytes
1st byte Master sends command;
Slave sends 0xC1 byte
3:0 MSB portion of data address.
2nd byte Master sends address;
Slave sends 0xC2 byte 7:0 LSB portion of data address.
3rd byte
(1st data byte)
Master sends data;
Slave sends ACK (0x41) 7:0 Data, LSB
... ... ... ...
Nth byte
(Last data byte)
Master sends data;
Slave sends ACK (0x41) 7:0 Data, MSB
(N + 1) byte Master sends CRC;
Slave sends ACK (0x41) 7:0 Optional CRC
Sync bytes
Master sends dummy;
Slave sends ACK (0x41) or
NACK (0x4E) byte
7:0
Master sends dummy byte; Slave responds with NACK if busy,
or with ACK when processing complete.
Master must receive ACK before starting the next transaction.
example, if synchronization is lost), the host only needs
to wait for the SPI to time out before restarting commu-
nication from the first command byte. SPI timeout count
starts after receiving the first command byte from the
master (after the 8th SPI clock of the first byte). The
count stops and clears after receiving the last byte of a
transaction (after the 8th SPI clock of the last byte).
If the timeout count expires (exceeds COM_TIMO)
before the transaction completes, the MAXQ3180 aban-
dons the unfinished transaction and resets the SPI logic
to be ready for the next transaction. The default SPI
timeout is 320ms.
Optionally, a CRC byte can be appended to each
transaction. For write commands, the CRC byte is sent
by the master, and for read commands the CRC byte is
sent by the MAXQ3180. The CRC mode is enabled
when the CRCEN bit is set to 1 in OPMODE1 register.
Otherwise, the MAXQ3180 assumes no CRC byte is
used. The 8-bit CRC is calculated for all bytes in a
transaction, from the first command byte sent by the
master through the last data byte excluding sync bytes,
using the polynomial P = x8+ x5+ x4+ 1. If the trans-
mitted CRC byte does not match the calculated CRC
byte (for a write command), the MAXQ3180 ignores the
command.
The length of the transfer is defined by the first com-
mand byte and the status of the CRCEN bit in the
OPMODE1 register. There is no special synchronization
mechanism provided in this simple protocol. Therefore,
the master is responsible for sending/receiving the cor-
rect number of bytes. If the master mistakenly sends
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
24 ______________________________________________________________________________________
more bytes than are required by the current command,
the extra bytes are either ignored (if the MAXQ3180 is
busy processing the previous command) or are inter-
preted as the beginning of a new command. If the mas-
ter sends fewer bytes than are required by the current
command, the MAXQ3180 waits for SPI timeout, then
drops the transaction and resets the communication
channel. The duration of the timeout can be configured
through the COM_TIMO register.
Figures 5 and 6 show typical 2-byte reading and writing
transfers (without CRC byte).
Host Software Design
Individual message bytes sent through the SPI are
processed in a software routine contained in the ROM
firmware. For this reason, it is necessary to provide a
delay between successive bytes. This byte spacing
must be no less than 400 system clocks to ensure that
the MAXQ3180 has a chance to read and process the
byte before the arrival of the next one.
To read any virtual power registers, the host must first
confirm that the DSPRDY bit of the IRQ_FLAG register
is set, which indicates the last DSP cycle has complet-
ed, then proceed to reading all the desired virtual
power registers. For best communication efficiency, it is
recommended to complete reading the virtual power
registers before reading other registers. Virtual power
register reads must be completed within 50% of DSP
cycle time, from the moment the DSPRDY bit is set. Do
not forget to clear the DSPRDY bit, otherwise, host soft-
ware is not able to detect the completion of the new
DSP cycle. The MAXQ3180 does not clear the bit; it
only sets the bit whenever a DSP cycle processing is
completed. Users can clear the bit directly after the
confirmation that the bit is set. Clearing the DSPRDY bit
does not affect the DSP processing. It is strongly rec-
ommended that CRC be enabled for both read and
write to achieve reliable communications.
SSEL
SCLK
MOSI
MISO
READING DATA FROM MAXQ3180 THROUGH SPI INTERFACE
00 01 ADDRESS DUMMY DUMMY DUMMY DUMMY
0xC1 0xC2 NACK (0x4E) DATA LSB DATA MSBACK (0x41)
SSEL
SCLK
MOSI
MISO
10 01 ADDRESS DUMMY DUMMY
0xC1 0xC2 ACK (0x41) NACK (0x4E) ACK (0x41)ACK (0x41)
WRITING DATA TO MAXQ3180 THROUGH SPI INTERFACE
DATA LSB DATA MSB
Figure 6. Write SPI Transfer
Figure 5. Read SPI Transfer
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 25
READ MAXQ3180
SEND COMMAND BYTE 1
GET 0xC1?
GET 0xC2?
EXIT
SPI TIMEOUT (320ms)
DELAY > 400 SYSCLK
SEND COMMAND BYTE 2
SEND 0x00
DELAY > 400 SYSCLK
SEND 0x00
GET DATA BYTE
DELAY > 400 SYSCLK
GET 0x4E?
GET 0x41?
DONE?
N
N
N
Y
N
WRITE MAXQ3180
SEND COMMAND BYTE 1
GET 0xC1?
GET 0xC2?
EXIT
SPI TIMEOUT (320ms)
DELAY > 400 SYSCLK
SEND COMMAND BYTE 2
SEND DATA BYTE
DELAY > 400 SYSCLK
SEND 0x00
DELAY > 400 SYSCLK
GET 0x4E?
GET 0x41?
DONE?
GET 0x41?
N
N
N
N
Y
N
Figure 8. Flowchart for Writing to MAXQ3180Figure 7. Flowchart for Reading from MAXQ3180
Register Set
Data and device command and control information are
located in internal registers. Registers range from 8 to 64
bits in length and are divided into RAM-based registers
and virtual registers. The RAM-based registers contain
both operating parameters and measurement results.
The virtual registers contain calculated values derived
from one or more real registers. They are calculated at
the time they are requested, and thus can involve addi-
tional time to return a value. Most virtual registers are 8
bytes in length and are delivered least significant byte
first.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
26 ______________________________________________________________________________________
Table 3. RAM Register Map
x0h x1h x2h x3h x4h x5h x6h x7h x8h x9h xAh xBh xCh xDh xEh xFh
0x00 STATUS OP
MODE0
OP
MODE1
OP
MODE2 IRQ_FLAG IRQ_MASK
SCAN
_IA
SCAN
_VA
SCAN
_IC
SCAN
_VC
SCAN
_IB
SCAN
_VB
SCAN
_IN
SCAN
_TE
0x01 AUX_CFG SYS_KHZ VOLT_CC AMP_CC PWR_CC ENR_CC CYCNT PLSCFG
1
PLSCFG
2
0x02 PLS1_WD THR1 PLS2_WD THR2 REJ_NS AVG_NS
0x03 AVG_C HPF_C B0FUND A1FUND B0HARM A1HARM
0x04 NS OCLVL OVLVL UVLVL NOLOAD R_ACFG R_ADCRATE
0x05 R_ADCACQ R_
SPICF NZX_TIMO COM_TIMO ACC_TIMO ZC_LPF I1THR I2THR
0x06 CHKSUM LINEFR
0x11 N.IRMS
0x12 N.I_GAIN
PHASE A CALIBRATION AND STATUS REGISTERS
0x13 A.I_GAIN A.V_GAIN A.E_GAIN A.EF_GAIN A.OFFS_HI A.GAIN_LO A.OFFS_LO A.PA0
0x14 A.PA1 A.PA2 A.
FLAGS
A.
MASK
A.
EOVER
A.
EFOVER
PHASE B CALIBRATION AND STATUS REGISTERS
0x21 B.I_GAIN B.V_GAIN
0x22 B.E_GAIN B.EF_GAIN B.OFFS_HI B.GAIN_LO B.OFFS_LO B.PA0 B.PA1 B.PA2
0x23 B.
FLAGS
B.
MASK
B.
EOVER
B.
EFOVER
PHASE C CALIBRATION AND STATUS REGISTERS
0x30 C.I_GAIN C.V_GAIN C.E_GAIN C.EF_GAIN
0x31 C.OFFS_HI C.GAIN_LO C.OFFS_LO C.PA0 C.PA1 C.PA2
C.
FLAGS
C.
MASK
C.
EOVER
C.
EFOVER
0x32
PHASE A MEASUREMENT REGISTERS*
0x1C A.PF A.VRMS A.IRMS
0x1D A.ACT A.REA A.APP A.ACTF
0x1E A.REAF A.APPF A.EAPOS A.EANEG
0x1F A.ERPOS A.ERNEG A.ES A.EAFPOS
0x20 A.EAFNEG A.ERFPOS A.ERFNEG A.ESF
PHASE B MEASUREMENT REGISTERS*
0x2B B.PF B.VRMS B.IRMS B.ACT
0x2C B.REA B.APP B.ACTF B.REAF
0x2D B.APPF B.EAPOS B.EANEG B.ERPOS
0x2E B.ERNEG B.ES B.EAFPOS B.EAFNEG
0x2F B.ERFPOS B.ERFNEG B.ESF
PHASE C MEASUREMENT REGISTERS*
0x39 C.PF
0x3A C.VRMS C.IRMS C.ACT C.REA
0x3B C.APP C.ACTF C.REAF C.APPF
0x3C C.EAPOS C.EANEG C.ERPOS C.ERNEG
0x3D C.ES C.EAFPOS C.EAFNEG C.ERFPOS
0x3E C.ERFNEG C.ESF
*
Read-only.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 27
x0 x1 x2 x3 x4 x5 x6 x7
0x80 PWRP.A PWRP.B PWRP.C PWRP.T
0x81 PWRQ.A PWRQ.B PWRQ.C PWRQ.T
0x82 PWRS.A PWRS.B PWRS.C PWRS.T
0x83 V.HARM V.A V.B V.C
0x84 I.N, I.HARM I.A I.B I.C
0x85 HARM_NF VBPH VCPH
0x86 PF.T
0x87 ENRS.A ENRS.B ENRS.C ENRS.T
0x88 PWRPF.A PWRPF.B PWRPF.C PWRPF.T
0x89 PWRQF.A PWRQF.B PWRQF.C PWRQF.T
0x8A PWRSF.A PWRSF.B PWRSF.C PWRSF.T
0x8B ENRSF.A ENRSF.B ENRSF.C ENRSF.T
0x8C ENRP.A ENRP.B ENRP.C ENRP.T
0x8D ENRQ.A ENRQ.B ENRQ.C ENRQ.T
0x8E ENRPF.A ENRPF.B ENRPF.C ENRPF.T
0x8F ENRQF.A ENRQF.B ENRQF.C ENRQF.T
SPECIAL FUNCTION REGISTERS
0xC0 DSPVER RAWTEMP ENTER STOP ENTER
LOWPM EXIT LOWPM
Table 4. Virtual Register Map
Note: All virtual registers are read-only.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
28 ______________________________________________________________________________________
RAM-Based Registers
The RAM-based registers contain both operating parameters and measurement results. They are divided into a num-
ber of categories that are described in the following sections.
General Operating Registers
Global Status Register (STATUS) (0x000)
This register contains bits that reflect the global status of the device.
Bit: 7 6 5 4 3 2 1 0
Name: — CROFF PORF WDTR — PHSEQ REVCFQ REVCFP
Reset: 0 0 0 0 0 0 0 0
BIT NAME FUNCTION
7, 3 Reserved.
6 CROFF
When set, the high-frequency crystal has failed and the MAXQ3180 is operating from its internal ring
oscillator. Under these circumstances, energy accumulation is not accurate and the SPI bus does not
operate at full speed.
5 PORF
When set, the last reset was due to power-on-reset. Host should clear this bit to allow the next POR
detection.
4 WDTR
When set, the last reset was caused by expired watchdog. The bit should be cleared (set to 0) by the
host to allow the next watchdog reset detection.
2 PHSEQ
0 = The sequence of voltages presented to the voltage inputs is (-A-B-C-).
1 = The sequence of voltages presented to the voltage inputs is reversed (-A-C-B-).
This bit is meaningful only for connection systems that include all three voltages.
1 REVCFQ
0 = The quantity being output on the CFQ pin is positive (direct).
1 = The quantity being output on the CFQ pin is negative (reverse).
0 REVCFP
0 = The quantity being output on the CFP pin is positive (direct).
1 = The quantity being output on the CFP pin is negative (reverse).
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 29
Operating Mode Register 1 (OPMODE1) (0x002)
BIT NAME FUNCTION
7:4 — Reserved.
3 CRCEN
If set, a 1-byte CRC is appended to the end of each SPI read and is expected at the end of each SPI
write. See the SPI Communication Protocols section for details about how to use the CRC byte for error
checking on the SPI bus.
2 POPOL
This bit sets the polarity of the output pulse generators. If clear, the pulse outputs are active low; that
is, they remain in the high state until a pulse event occurs, at which time they switch low for one
pulse-width interval before reverting to the high state. If set, the pulse outputs are active high; that is,
they remain in the low state until a pulse event occurs, at which time they switch to the high state for
one pulse-width interval before reverting to the low state.
Bit: 7 6 5 4 3 2 1 0
Name: — — — CRCEN POPOL CONCFG
Reset: 0 0 0 0 0 0 0x0
Operating Mode Register 0 (OPMODE0) (0x001)
BIT NAME FUNCTION
7:5, 0 Reserved.
4 EXTCLK
When set, the high-frequency crystal oscillator is disabled and the XTAL1 pin is configured to be a
clock input for the device. This is used when it is desired to operate multiple devices from the same
clock source for purposes of maintaining synchronization.
3 SWRES
When set, forces the internal software to restart from the reset vector. This has the same effect as a
power-on reset, but does not specifically reset any hardware peripherals. This bit is automatically
cleared after the reset.
2 DSPDIS
When set, disables the signal processing software routines. The CPU continues to run at full speed,
but only to perform supervisory functions (such as servicing the SPI port).
1 LOWPM
When set, causes the CPU to switch its clock source from the external crystal to an internal ring oscillator
that operates at a nominal frequency of 1MHz. In this mode, the CPU continues to run, but the host must
reconfigure the parameters configured for crystal operation (such as filter settings, timeouts, and pulse
widths).
Bit: 7 6 5 4 3 2 1 0
Name: — EXTCLK SWRES DSPDIS LOWPM
Reset: 0 0 0 0 0 0 0 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
30 ______________________________________________________________________________________
Operating Mode Register 1 (OPMODE1) (0x002) (continued)
BIT NAME FUNCTION
These bits determine how power is calculated on each of the three phases.
00
PA = IA x VA
PB = IB x VB
PC = IC x VC
Use this configuration when the load is
connected in a wye arrangement and
neutral is connected to MAXQ3180 ground,
or when the load is connected in a delta
arrangement and isolated voltage and
current sensors are used. This
arrangement measures power in each load
branch rather than power in each source
branch.
01
PA = IA x VA
PB = IB x (-VC)
PC = IC x VC
Use this configuration when the load is
connected in a four-wire delta
arrangement. In this arrangement, the BC
leg is split and VB-N is expected to be
equal to -VC-N. Voltages are referenced to
neutral.
10
PA = IA x VA
PB = IB x (-VA - VC)
PC = IC x VC
Use this configuration when the load is
connected in a four-wire wye arrangement,
but only two voltage sensors are
available. When connected in this way,
phase B is assumed to be ground.
1:0 CONCFG
11
PA = IA x VA
PB = IB x (VA - VC)
PC = IC x VC
Use this configuration when the load is
connected as a three-wire delta and it is
desired to measure the voltage and current
inside the delta legs, but to calculate the
power in each of the source circuits. When
connected this way, source phase B is
considered ground.
V
I
II
VV
I
I
I
V V
V
I
I
V
VV
I
V
I
II
V
N
V
I
I
V
V
I
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 31
Operating Mode Register 2 (OPMODE2) (0x003)
BIT NAME FUNCTION
7 — Reserved.
6 DHARA
When set, disables automatic determination of the filter parameters for the harmonic filter coefficient. If
set by the host software, the host must set a value in the A1HARM filter coefficient register to
establish the operating frequency of this filter if harmonic-mode calculations are used. When cleared,
the MAXQ3180 automatically determines the value of the harmonic-filter coefficient based on the
measured line frequency and the harmonic-order requested (AUX_CFG.ORDH).
5 DFUNA
When set, disables automatic determination of the filter parameters for the fundamental-mode filter
described above. If set by the host software, the host must set a value in the A1FUND filter coefficient
register to establish the operating frequency of this filter if fundamental-mode calculations are used.
When clear, the MAXQ3180 automatically determines the value of the fundamental-mode filter
coefficient based on the measured line frequency.
4 DFUN
When set, fundamental-mode calculations are disabled. Fundamental-mode calculations provide
information about power and energy that are consumed only at the fundamental line frequency apart
from any harmonics that could be present. Setting this bit disables all fundamental frequency registers
but allows the MAXQ3180 to calculate other parameters at a higher rate. Set this bit when (1)
fundamental mode values do not need to be read, and (2) R_ADCRATE needs to be reduced below its
default value.
3 LINFRM
Selects the current linearity offset calibration method. See the Calibrating Current Offset section for
more information.
0 =
IRMS
2
+OFFS
1 = IRMS + OFFS
These bits select the coefficient used in calculating apparent power.
00 = 1-phase, 3-wire (1P3W), or 3-phase, 4-wire (3P4W) (C = 1)
01 = 3-phase, 3-wire (3P3W) (C = 3/2)
10 = three voltages, three currents (3V3A) (C = 3/3)
2:1 WIRSYS
3P3W Wiring (01)
Bit: 7 6 5 4 3 2 1 0
Name: — DHARA DFUNA DFUN LINFRM WIRSYS APPSEL
Reset: 0 0 0 0 0 0 0 0
IA
IC
VAB
VCB
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
32 ______________________________________________________________________________________
Operating Mode Register 2 (OPMODE2) (0x003) (continued)
BIT NAME FUNCTION
3P4W Wiring (00)
3V3A (10)
2:1 WIRSYS
1P3W (00)
Selects the mechanism to use for calculating apparent power.
0: S = VRMS x IRMS Apparent power is calculated by multiplying, on a per-DSP cycle basis, the
product of the RMS volts and RMS amps.
0 APPSEL
1:
S=P2+Q2
Apparent power is calculated by finding the length of the power vector.
IA
IC
IB
VAB VAC
VBC
IA
N
IB
VAN
VBN
V
IA
IBIC
V
N
VB
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 33
The interrupt request flag register contains bits that indicate the reason the IRQ pin has become active. The active
bit must be cleared by the host to avoid continuing firing of the interrupt by the MAXQ3180.
BIT NAME FUNCTION
15 DSPOR
When set, the DSP was unable to complete processing one cycle when another cycle was due to
begin. This indicates that the R_ADCRATE is set too low, and that samples are arriving more quickly
than they can be processed. Either increase the value of the R_ADCRATE register or set the DFUN bit
in the OPMODE2 register to disable fundamental frequency calculations to reduce the load on the DSP.
14 DSPRDY Set when the DSP cycle completes.
13 DCHR
When set, the direction of reactive energy flow has changed (that is, from capacitive to inductive or
from inductive to capacitive).
12 DCHA
When set, the direction of real energy flow has changed (that is, from toward the load to away from the
load, or from away from the load to toward the load).
11 NOZX
When set, the MAXQ3180 has failed to detect zero crossings on one or more voltage channels for the
time defined by the NZX_TIMO register.
10 UV
When set, the absolute instantaneous voltage level in one or more voltage channels failed to exceed
the trip level set in the UVLVL (Undervoltage Level) register for one DSP cycle.
9 OV
When set, the absolute instantaneous voltage level in one or more voltage channels has exceeded the
trip level set in the OVLVL (Overvoltage Level) register.
8 OC
When set, the absolute instantaneous current in one or more current channels has exceeded the trip
level set in the OCLVL (Overcurrent Level) register.
7:3 — Reserved.
2 EOVF When set, one or more energy accumulators have an MSB overflow condition.
1 CHSCH
When set, indicates a change of the CHKSUM. The CHKSUM is computed over the configuration and
calibration data. The host should review a change in CHKSUM because any change in the
configuration or calibration data affects the metering operation and accuracy.
0 PWRF
When set, a power-supply failure is imminent and the supervisory processor should begin taking steps
to save its state and prepare for a loss of power.
Global Interrupt Registers
Interrupt Request Flag Register (IRQ_FLAG) (0x004)
Bit: 15 14 13 12 11 10 9 8
Name: DSPOR DSPRDY DCHR DCHA NOZX UV OV OC
Reset: 0 0 0 0 0 0 0 0
Bit: 7 6 5 4 3 2 1 0
Name: — — — — EOVF CHSCH PWRF
Reset: 0 0 0 0 0 0 0 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
34 ______________________________________________________________________________________
Interrupt Mask Register (IRQ_MASK) (0x006)
BIT NAME FUNCTION
15 EDSPOR When set, this flag causes the IRQ pin to become active.
14 EDSPRDY When set, this flag causes the IRQ pin to become active.
13 EDCHR
When set, this flag causes the IRQ pin to become active when the direction of reactive energy flow has
been observed to have changed (that is, from capacitive to inductive or from inductive to capacitive).
12 EDCHA
When set, this flag causes the IRQ pin to become active when the direction of real energy flow has
been observed to have changed (that is, from toward the load to away from the load, or from away from
the load to toward the load).
11 ENOZX
When set, this flag causes the IRQ pin to become active when the MAXQ3180 has failed to detect zero
crossings on one or more voltage channels for at least one DSP cycle.
10 EUV
When set, this flag causes the IRQ pin to become active when the absolute instantaneous voltage
level in one or more voltage channels failed to exceed the trip level set in the UVLVL (Undervoltage
Level) register for one DSP cycle.
9 EOV
When set, this flag causes the IRQ pin to become active when the absolute instantaneous voltage
level in one or more voltage channels has exceeded the trip level set in the OVLVL (Overvoltage Level)
register.
8 EOC
When set, this flag causes the IRQ pin to become active when absolute instantaneous current in one
or more current channels has exceeded the trip level set in the OCLVL (Overcurrent Level) register.
7:3 — Reserved.
2 EEOVF
When set, this flag causes the IRQ pin to become active when one or more energy accumulators have
an overflow condition from their MSB.
1 ECHSCH When set, this flag enables the IRQ pin to become active when a CHKSUM change is detected.
0 EPWRF
When set, this flag causes the IRQ pin to become active when a power-supply failure is imminent and
the supervisory processor should begin taking steps to save its state and prepare for a loss of power.
Bit: 15 14 13 12 11 10 9 8
Name: EDSPOR EDSPRDY EDCHR EDCHA ENOZX EUV EOV EOC
Reset: 0 0 0 0 0 0 0 0
Bit: 7 6 5 4 3 2 1 0
Name: — — — — EEOVF ECHSCH EPWRF
Reset: 0 0 0 0 0 0 0 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 35
Meter Pulse Configuration
Pulse Configuration—CFP Output (PLSCFG1) (0x01E)
This register selects which phases are included in the CFP pulse output and also selects which quantity is accumu-
lated to drive the pulse output.
Bit: 7 6 5 4 3 2 1 0
Name: QNSEL PHASEC PHASEB PHASEA
Reset: 0x0 0 0 0
BIT NAME FUNCTION
7:3 QNSEL
CFP Pulse Output Source Select. This five-bit field determines what meter value will be accumulated in
each of the phases to produce the CFP pulse output. All other values are reserved.
00000 = Net real energy
00001 = Absolute real energy
00010 = Net reactive energy
00011 = Absolute reactive energy
00100 = Apparent energy
00110 = IRMS
00111 = VRMS
01000 = Real energy delivered to load
01001 = Real energy delivered to line
01010 = Reactive energy, quadrant I
01011 = Reactive energy, quadrant II
01100 = Reactive energy, quadrant III
01101 = Reactive energy, quadrant IV
2 PHASEC CFP Phase C Inclusion. When this bit is set, phase C is included in CFP pulse generation.
1 PHASEB CFP Phase B Inclusion. When this bit is set, phase B is included in CFP pulse generation.
0 PHASEA CFP Phase A Inclusion. When this bit is set, phase A is included in CFP pulse generation.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
36 ______________________________________________________________________________________
Pulse Configuration—CFQ Output (PLSCFG2) (0x01F)
This register selects which phases are included in the CFQ pulse output and also selects which quantity is accumu-
lated to drive the pulse output.
BIT NAME FUNCTION
7:3 QNSEL
CFQ Pulse Output Source Select. This five-bit field determines what meter value is accumulated in
each of the phases to produce the CFQ pulse output. All other values are reserved.
00000 = Net real energy
00001 = Absolute real energy
00010 = Net reactive energy
00011 = Absolute reactive energy
00100 = Apparent energy
00110 = IRMS
00111 = VRMS
01000 = Real energy delivered to load
01001 = Real energy delivered to line
01010 = Reactive energy, quadrant I
01011 = Reactive energy, quadrant II
01100 = Reactive energy, quadrant III
01101 = Reactive energy, quadrant IV
2 PHASEC CFQ Phase C Inclusion. When this bit is set, phase C is included in CFQ pulse generation.
1 PHASEB CFQ Phase B Inclusion. When this bit is set, phase B is included in CFQ pulse generation.
0 PHASEA CFQ Phase A Inclusion. When this bit is set, phase A is included in CFQ pulse generation.
Bit: 7 6 5 4 3 2 1 0
Name: QNSEL PHASEC PHASEB PHASEA
Reset: 0x0 0 0 0
CFP Pulse Width (PLS1_WD) (0x020)
This register designates the width of the CFP pulse, that is, the duration of the period that the CFP pulse is in the
active state. This value is given in ADC frame times (about 320μs). The default value of 0x9C (156 decimal) provides
a pulse width of about 50ms.
Bit: 15 14 13 12 11 10 9 8
Name: CFP Pulse-Width High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: CFP Pulse-Width Low Byte
Reset: 0x9C
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 37
CFP Pulse Threshold (THR1) (0x022)
This register designates the threshold of the CFP pulse. This value is used to set the meter constant for the CFP
pulse output. When the CFP pulse accumulator exceeds the value set in this register, the CFP pulse output is activat-
ed and the CFP pulse accumulator is reduced by the amount in this register.
CFQ Pulse Width (PLS2_WD) (0x026)
This register designates the width of the CFQ pulse; that is, the duration of the period that the CFQ pulse is in the
active state. This value is given in ADC frame times (about 320μs). The default value of 0x9C (156 decimal) provides
a pulse width of about 50ms.
Bit: 31 30 29 28 27 26 25 24
Name: THR1 Byte 3
Reset: 0x00
Bit: 23 22 21 20 19 18 17 16
Name: THR1 Byte 2
Reset: 0x10
Bit: 15 14 13 12 11 10 9 8
Name: THR1 Byte 1
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: THR1 Byte 0
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: CFQ Pulse-Width High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: CFQ Pulse-Width Low Byte
Reset: 0x9C
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
38 ______________________________________________________________________________________
CFQ Pulse Threshold (THR2) (0x028)
This register designates the threshold of the CFQ pulse. This value is used to set the meter constant for the CFQ
pulse output. When the CFQ pulse accumulator exceeds the value set in this register, the CFQ pulse output is acti-
vated and the CFQ pulse accumulator is reduced by the amount in this register.
Calibration Registers
Current Gain, Phase X = A/B/C/N (X.I_GAIN) (A: 0x130, B: 0x21C, C: 0x308, N: 0x12E)
This register contains gain coefficient for phase X current channel. The raw values are taken from the selected mea-
surement quantity and scaled by the factor:
Note: Bit 15 of this register must be set to zero for correct operation.
XI GAIN._
214
Bit: 31 30 29 28 27 26 25 24
Name: THR2 Byte 3
Reset: 0x00
Bit: 23 22 21 20 19 18 17 16
Name: THR2 Byte 2
Reset: 0x10
Bit: 15 14 13 12 11 10 9 8
Name: THR2 Byte 1
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: THR2 Byte 0
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Current Gain Coefficient High Byte
Reset: 0x40
Bit: 7 6 5 4 3 2 1 0
Name: Current Gain Coefficient Low Byte
Reset: 0x00
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 39
Voltage Gain, Phase X = A/B/C (X.V_GAIN) (A: 0x132, B: 0x21E, C: 0x30A)
This register contains gain coefficient for phase X voltage channel. The raw values are taken from the selected mea-
surement quantity and scaled by the factor:
Note: Bit 15 of this register must be set to zero for correct operation.
Energy Gain, Phase X = A/B/C (X.E_GAIN) (A: 0x134, B: 0x220, C: 0x30C)
This register contains gain coefficient for phase X energy. The raw values are taken from the selected measurement
quantity and scaled by the factor:
Note: Bit 15 of this register must be set to zero for correct operation.
Phase-Angle Compensation, High Range, Phase X = A/B/C (X.PA0)
(A: 0x13E, B: 0x22A, C: 0x316)
This signed register contains the angle as a fraction of one radian to add to the measured phase angle when the
measured current is above the value given in I1THR. This signed value ranges from -0.5 radian (at a value of
0x8000) to +(0.5 - 2-16) radian (at a value of 0x7FFF).
XE GAIN._
214
X V GAIN._
214
Bit: 15 14 13 12 11 10 9 8
Name: Voltage Gain Coefficient High Byte
Reset: 0x40
Bit: 7 6 5 4 3 2 1 0
Name: Voltage Gain Coefficient Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Energy Gain Coefficient High Byte
Reset: 0x40
Bit: 7 6 5 4 3 2 1 0
Name: Energy Gain Coefficient Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Phase-Angle Offset High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Phase-Angle Offset Low Byte
Reset: 0x00
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
40 ______________________________________________________________________________________
Phase-Angle Compensation, Medium Range, Phase X = A/B/C (X.PA1)
(A: 0x140, B: 0x22C, C: 0x318)
This signed register contains the angle, as a fraction of one radian, to add to the measured phase angle when the
measured current is between the values given in I1THR and I2THR. This signed value ranges from -0.5 radian (at a
value of 0x8000) to +(0.5 - 2-16) radian (at a value of 0x7FFF).
Phase-Angle Compensation, Low Range, Phase X = A/B/C (X.PA2)
(A: 0x142, B: 0x22E, C: 0x31A)
This signed register contains the angle, as a fraction of one radian, to add to the measured phase angle when the
measured current is below the value given in I2THR. This signed value ranges from -0.5 radian (at a value of 0x8000)
to +(0.5 - 2-16) radian (at a value of 0x7FFF).
Limit Registers
Overcurrent Level (OCLVL) (0x044)
This register specifies the fraction of full-scale current that is declared to be an overcurrent condition. When X.IRMS
exceeds this level for one DSP cycle, the OCF flag in the X.FLAGS register is set. If the OCM flag is set in the
X.MASK register, setting the OCF flag will cause the interrupt bit OC to be set in the IRQ_FLAG register. If the inter-
rupt is enabled, the interrupt pin is driven active. Full scale is represented by 0x10000. The maximum value for this
register is 0xFFFF.
Bit: 15 14 13 12 11 10 9 8
Name: Phase-Angle Offset High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Phase-Angle Offset Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Phase-Angle Offset High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Phase-Angle Offset Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Overcurrent Level High Byte
Reset: 0xFF
Bit: 7 6 5 4 3 2 1 0
Name: Overcurrent Level Low Byte
Reset: 0xFF
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 41
Overvoltage Level (OVLVL) (0x046)
This register specifies the fraction of full-scale voltage that is declared to be an overvoltage condition. When X.VRMS
exceeds this level for one DSP cycle, the OVF flag in the X.FLAGS register is set. If the OVM flag is set in the
X.MASK register, setting the OVF flag will cause the interrupt bit OV to be set in the IRQ_FLAG register. If the inter-
rupt is enabled, the interrupt pin is driven active. Full scale is represented by 0x10000. The maximum value for this
register is 0xFFFF.
Undervoltage Level (UVLVL) (0x048)
This register specifies the fraction of full-scale voltage below which an undervoltage condition is declared. When
X.VRMS falls below this level for one DSP cycle, the UVF flag in the X.FLAGS register is set. If the UVM flag is set in
the X.MASK register, setting the UVF flag will cause the interrupt bit UV to be set in the IRQ_FLAG register. If the
interrupt is enabled, the interrupt pin is driven active. Full scale is represented by 0x10000. The maximum value for
this register is 0xFFFF.
No-Load Level (NOLOAD) (0x04A)
This register specifies the fraction of full-scale current below which a no-load condition is declared. When X.IRMS
falls below this level, the MAXQ3180 no longer accumulates power for phase X. Full scale is represented by
0x10000. The maximum value for this register is 0xFFFF.
Bit: 15 14 13 12 11 10 9 8
Name: Overvoltage Level High Byte
Reset: 0xFF
Bit: 7 6 5 4 3 2 1 0
Name: Overvoltage Level Low Byte
Reset: 0xFF
Bit: 15 14 13 12 11 10 9 8
Name: Undervoltage Level High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Undervoltage Level Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: No-Load Level High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: No-Load Level Low Byte
Reset: 0x03
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
42 ______________________________________________________________________________________
Phase Status Registers
Interrupt Flags, Phase X = A/B/C (X.FLAGS) (A: 0x144, B: 0x230, C: 0x31C)
The X.FLAGS register contains condition flags that relate to the function of phase X (A/B/C) measurements. Once
set, these bits can be cleared only by the host.
Bit: 7 6 5 4 3 2 1 0
Name: — DCHRF DCHAF NOZXF UVF OVF OCF
Reset: 0 0 0 0 0 0 0 0
BIT NAME FUNCTION
7:6 — Reserved.
5 DCHRF
Reactive Energy Direction Change. Set when the direction of reactive power flow changes (from
capacitive to inductive or from inductive to capacitive). If the DCHRM bit is set, this bit sets the DCHR
flag in the IRQ_FLAG register.
4 DCHAF
Real Energy Direction Change. Set when the direction of real power flow changes (from toward the load
to toward the line, or from toward the line to toward the load). If the DCHAM bit is set, this bit sets the
DCHA flag in the IRQ_FLAG register.
3 NOZXF
No-Zero Crossing. Set when the voltage waveform in phase X fails to exhibit a zero crossing during
NZX_TIMO of the ADC sample periods. If the NOZXM bit is set, this bit sets the NOZX flag in the
IRQ_FLAG register.
2 UVF
Undervoltage. Set when the RMS voltage in phase X falls below the undervoltage threshold set in
UVLVL. If the UVM bit is set, this bit sets the UV flag in the IRQ_FLAG register.
1 OVF
Overvoltage. Set when the RMS voltage in phase X exceeds the overvoltage threshold set in OVLVL. If
the OVM bit is set, this bit sets the OV flag in the IRQ_FLAG register.
0 OCF
Overcurrent. Set when the RMS current in phase X exceeds the overcurrent threshold set in OCLVL. If
the OCM bit is set, this bit sets the OC flag in the IRQ_FLAG register.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 43
Interrupt Mask, Phase X = A/B/C (X.MASK) (A: 0x145, B: 0x231, C: 0x31D)
Energy Overflow Flags, Phase X = A/B/C (X.EOVER) (A: 0x146, B: 0x232, C: 0x31E)
These bits indicate that an overflow condition has occurred on an energy accumulator. An overflow condition is not
an error condition. Rather, it simply indicates that the value in the energy accumulator could be smaller than the pre-
vious reading due to the overflow in the counter. To obtain the actual energy usage since the previous reading,
0x100000000 must be added to the difference. These bits, once set, can be cleared only by the host.
Bit: 7 6 5 4 3 2 1 0
Name: DIR_R DIR_A DCHRM DCHAM NOZXM UVM OVM OCM
Reset: 0 0 0 0 0 0 0 0
BIT NAME FUNCTION
7 DIR_R
Reactive Energy Direction Status
0 = positive
1 = negative
6 DIR_A
Active Energy Direction Status
0 = positive
1 = negative
5 DCHRM
Reactive Energy Direction Change Mask. If set, a change in reactive power direction on phase X
causes the DCHR flag in the IRQ_FLAG register to be set.
4 DCHAM
Real Energy Direction Change Mask. If set, a change in real power direction on phase X causes the
DCHA flag in the IRQ_FLAG register to be set.
3 NOZXM
No-Zero Crossing Mask. If set, a no-zero crossing on phase X causes the NOZX flag in the IRQ_FLAG
register to be set.
2 UVM
Undervoltage Mask. If set, an undervoltage condition on phase X causes the UV flag in the IRQ_FLAG
register to be set.
1 OVM
Overvoltage Mask. If set, an overvoltage condition on phase X causes the OV flag in the IRQ_FLAG
register to be set.
0 OCM
Overcurrent Mask. If set, an overcurrent condition on phase X causes the OC flag in the IRQ_FLAG
register to be set.
BIT NAME FUNCTION
7:5 — Reserved.
4 SOV When set, indicates an overflow condition on the apparent energy accumulator.
3 RNOV When set, indicates an overflow condition on the reactive negative energy accumulator.
2 RPOV When set, indicates an overflow condition on the reactive positive energy accumulator.
1 ANOV When set, indicates an overflow condition on the real negative energy accumulator.
0 APOV When set, indicates an overflow condition on the real positive energy accumulator.
Bit: 7 6 5 4 3 2 1 0
Name: — SOV RNOV RPOV ANOV APOV
Reset: 0 0 0 0 0 0 0 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
44 ______________________________________________________________________________________
Measurements
Line Frequency (LINEFR) (0x062)
Line frequency, LSB = 0.001Hz.
Power Factor, Phase X = A/B/C (X.PF) (A: 0x1C6, B: 0x2B2, C: 0x39E)
Power factor of phase A/B/C, LSB = 1/214. Note that the power factors are signed integers, and a negative value
indicates a reversed power flow direction.
RMS Voltage, Phase X = A/B/C (X.VRMS) (A: 0x1C8, B: 0x2B4, C: 0x3A0)
This register provides the raw RMS voltage over the most recent DSP cycle, LSB = VFS/224.
Bit: 15 14 13 12 11 10 9 8
Name: Line Frequency High Byte
Reset:
Bit: 7 6 5 4 3 2 1 0
Name: Line Frequency Low Byte
Reset:
Bit: 15 14 13 12 11 10 9 8
Name: Power Factor High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Power Factor Low Byte
Reset: 0x00
Bit: 31 30 29 28 27 26 25 24
Name: RMS Voltage Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: RMS Voltage Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: RMS Voltage Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: RMS Voltage Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 45
RMS Current, Phase X = A/B/C (X.IRMS) (A: 0x1CC, B: 0x2B8, C: 0x3A4)
This register provides the raw RMS current over the most recent DSP cycle, LSB = IFS/224.
Energy, Real Positive, Phase X = A/B/C (X.EAPOS)
(A: 0x1E8, B: 0x2D4, C: 0x3C0)
On every DSP cycle, the contents of the X.ACT register are tested, and, if positive, are added to this register. When
this register overflows, the APOV bit in the X.EOVER register is set.
Bit: 31 30 29 28 27 26 25 24
Name: RMS Current Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: RMS Current Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: RMS Current Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: RMS Current Byte 0
Bit: 31 30 29 28 27 26 25 24
Name: Real Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Real Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Real Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Real Energy Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
46 ______________________________________________________________________________________
Energy, Real Negative, Phase X = A/B/C (X.EANEG)
(A: 0x1EC, B: 0x2D8, C: 0x3C4)
On every DSP cycle, the contents of the X.ACT register are tested, and, if negative, absolute values are added to
this register. When this register overflows, the ANOV bit in the X.EOVER register is set.
Energy, Reactive Positive, Phase X = A/B/C (X.ERPOS)
(A: 0x1F0, B: 0x2DC, C: 0x3C8)
On every DSP cycle, the contents of the X.REA register are tested, and, if positive, are added to this register. When
this register overflows, the RPOV bit in the X.EOVER register is set.
Bit: 31 30 29 28 27 26 25 24
Name: Real Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Real Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Real Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Real Energy Byte 0
Bit: 31 30 29 28 27 26 25 24
Name: Reactive Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Reactive Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Reactive Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Reactive Energy Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 47
Energy, Reactive Negative, Phase X = A/B/C (X.ERNEG)
(A: 0x1F4, B: 0x2E0, C: 0x3CC)
On every DSP cycle, the contents of the X.REA register are tested, and, if negative, absolute values are added to
this register. When this register overflows, the RNOV bit in the X.EOVER register is set.
Energy, Apparent, Phase X = A/B/C (X.ES) (A: 0x1F8, B: 0x2E4, C: 0x3D0)
On every DSP cycle, the contents of the X.APP register are added to this register. When this register overflows, the
SOV bit in the X.EOVER register is set.
Bit: 31 30 29 28 27 26 25 24
Name: Reactive Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Reactive Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Reactive Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Reactive Energy Byte 0
Bit: 31 30 29 28 27 26 25 24
Name: Apparent Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Apparent Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Apparent Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Apparent Energy Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
48 ______________________________________________________________________________________
Virtual Register Conversion Coefficients
Voltage Units Conversion Coefficient (VOLT_CC) (0x014)
This register contains the value by which the raw voltage value in each phase (A.VRMS, B.VRMS, and C.VRMS) is
multiplied before being presented to the virtual RMS voltage registers (V.A, V.B, and V.C).
To determine the value of VOLT_CC, a voltage value for the least significant bit (VOLT_LSB) of the V.X registers must
be selected. Typical values might range from 1mV to 1nV. To avoid significant conversion loss, VOLT_LSB should be
chosen such that VOLT_CC is >1000. Once VOLT_LSB is determined, calculate VOLT_CC from the following equa-
tion:
Current Units Conversion Coefficient (AMP_CC) (0x016)
This register contains the value by which the raw current value in each phase (A.IRMS, B.IRMS, C.IRMS, and
N.IRMS) is multiplied before being presented to the virtual RMS current registers (I.A, I.B, I.C, and I.N). To determine
the value of AMP_CC, a current value for the least significant bit (AMP_LSB) of the I.X registers must be selected.
Typical values might range from 1nA to 10μA. To avoid significant conversion loss, AMP_LSB should be chosen
such that AMP_CC is >1000. Once determined, calculate AMP_CC from the following equation:
AMP CC I
AMP LSB
FS
__
=×224
VOLT CC V
VOLT LSB
FS
__
=×224
Bit: 15 14 13 12 11 10 9 8
Name: Voltage Units Conversion Coefficient High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Voltage Units Conversion Coefficient Low Byte
Reset: 0x01
Bit: 15 14 13 12 11 10 9 8
Name: Current Units Conversion Coefficient High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Current Units Conversion Coefficient Low Byte
Reset 0x01
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 49
Power Units Conversion Coefficient (PWR_CC) (0x018)
This register contains the value by which the raw power value in each phase is multiplied before being presented to
the virtual power registers. The table below lists the raw power registers and the corresponding virtual registers.
PWR_CC establishes the amount of power represented by one PWR_LSB of the power registers. To avoid significant
conversion loss, PWR_LSB should be chosen such that PWR_CC is > 1000. Calculate the value of PWR_CC accord-
ing to the following formula:
PWR CC IV
PWR LSB
FS FS
__
=×
×232
Bit: 15 14 13 12 11 10 9 8
Name: Power Units Conversion Coefficient High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Power Units Conversion Coefficient Low Byte
Reset: 0x01
DESCRIPTION RAW VIRTUAL
Real power, phase A A.ACT PWRP.A
Real power, phase B B.ACT PWRP.B
Real power, phase C C.ACT PWRP.C
Real power, total — PWRP.T
Reactive power, phase A A.REA PWRQ.A
Reactive power, phase B B.REA PWRQ.B
Reactive power, phase C C.REA PWRQ.C
Reactive power, total — PWRQ.T
Apparent power, phase A A.APP PWRS.A
Apparent power, phase B B.APP PWRS.B
Apparent power, phase C C.APP PWRS.C
Apparent power, total — PWRS.T
Real power, phase A, fundamental frequency only A.ACTF PWRPF.A
Real power, phase B, fundamental frequency only B.ACTF PWRPF.B
Real power, phase C, fundamental frequency only C.ACTF PWRPF.C
Real power, total, fundamental frequency only PWRPF.T
Reactive power, phase A, fundamental frequency only A.REAF PWRQF.A
Reactive power, phase B, fundamental frequency only B.REAF PWRQF.B
Reactive power, phase C, fundamental frequency only C.REAF PWRQF.C
Reactive power, total, fundamental frequency only PWRQF.T
Apparent power, phase A, fundamental frequency only A.APPF PWRSF.A
Apparent power, phase B, fundamental frequency only B.APPF PWRSF.B
Apparent power, phase C, fundamental frequency only C.APPF PWRSF.C
Apparent power, total, fundamental frequency only PWRSF.T
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
50 ______________________________________________________________________________________
Energy Units Conversion Coefficient (ENR_CC) (0x01A)
This register contains the value by which the raw accumulated energy value in each phase is multiplied before being
presented to the virtual energy registers. The table below lists the raw energy accumulators and the corresponding
virtual registers.
Bit: 15 14 13 12 11 10 9 8
Name: Energy Units Conversion Coefficient High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Energy Units Conversion Coefficient Low Byte
Reset: 0x01
DESCRIPTION RAW VIRTUAL
Real energy, phase A, positive direction A.EAPOS
Real energy, phase A, reverse direction A.EANEG ENRP.A*
Real energy, phase B, positive direction B.EAPOS
Real energy, phase B, reverse direction B.EANEG ENRP.B*
Real energy, phase C, positive direction C.EAPOS
Real energy, phase C, reverse direction C.EANEG ENRP.C*
Real energy, total — ENRP.T
Reactive energy, phase A, positive direction A.ERPOS
Reactive energy, phase A, reverse direction A.ERNEG ENRQ.A*
Reactive energy, phase B, positive direction B.ERPOS
Reactive energy, phase B, reverse direction B.ERNEG ENRQ.B*
Reactive energy, phase C, positive direction C.ERPOS
Reactive energy, phase C, reverse direction C.ERNEG ENRQ.C*
Reactive energy, total — ENRQ.T
Apparent energy, phase A A.ES ENRS.A
Apparent energy, phase B B.ES ENRS.B
Apparent energy, phase C C.ES ENRS.C
Apparent energy, total — ENRS.T
Real energy, phase A, positive direction, fundamental only A.EAFPOS
Real energy, phase A, reverse direction, fundamental only A.EAFNEG ENRPF.A*
Real energy, phase B, positive direction, fundamental only B.EAFPOS
Real energy, phase B, reverse direction, fundamental only B.EAFNEG ENRPF.B*
Real energy, phase C, positive direction, fundamental only C.EAFPOS
Real energy, phase C, reverse direction, fundamental only C.EAFNEG ENRPF.C*
Real energy, total, fundamental only ENRPF.T
Reactive energy, phase A, positive direction, fundamental only A.ERFPOS
Reactive energy, phase A, reverse direction, fundamental only A.ERFNEG ENRQF.A*
Reactive energy, phase B, positive direction, fundamental only B.ERFPOS
Reactive energy, phase B, reverse direction, fundamental only B.ERFNEG ENRQF.B*
*
These registers represent the algebraic sum of the positive and reverse energy in the two “raw” registers noted. Thus, the energy
returned in these virtual registers represents the net energy.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 51
Energy Units Conversion Coefficient (ENR_CC) (0x01A) (continued)
DESCRIPTION RAW VIRTUAL
Reactive energy, phase C, positive direction, fundamental only C.ERFPOS
Reactive energy, phase C, reverse direction, fundamental only C.ERFNEG ENRQF.C*
Reactive energy, total, fundamental only ENRQF.T
Apparent energy, phase A, fundamental only A.ESF ENRSF.A
Apparent energy, phase B, fundamental only B.ESF ENRSF.B
Apparent energy, phase C, fundamental only C.ESF ENRSF.C
Apparent energy, total, fundamental only ENRSF.T
To avoid significant conversion loss, ENR_LSB should be chosen such that ENR_CC is > 1000. Calculate the value
of ENR_CC according to the following formula:
Virtual Registers
The virtual registers are calculated values derived from one or more real registers. They are calculated at the time
they are requested, and thus could involve additional time to return a value. Most virtual registers are 8 bytes in
length and are delivered least significant byte first.
Power
Real Power, Phase X = A/B/C/T (PWRP.X) (A: 0x801, B: 0x802, C: 0x804, T: 0x807)
This signed register contains the real instantaneous power delivered into phase A/B/C or total. Power is calculated
from the instantaneous energy measurement according to the following equation:
The register is 8 bytes long, but the most significant 2 bytes are not used. See the PWR_CC register description for
more details.
Note that the sign bit is bit 47 for all 8-byte signed virtual registers.
PWRP X XACT PWR CC
NS
.._
=××216
ENR CC IVt
ENR LSB
FS FS FR
__
=××
×216
*
These registers represent the algebraic sum of the positive and reverse energy in the two “raw” registers noted. Thus, the energy
accumulated in these virtual registers represents the net energy.
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
52 ______________________________________________________________________________________
Reactive Power, Phase X = A/B/C/T (PWRQ.X) (A: 0x811, B: 0x812, C: 0x814, T: 0x817)
This signed register contains the reactive instantaneous power delivered into phase A/B/C or total. Power is calculat-
ed from the instantaneous energy measurement according to the following equation:
The register is 8 bytes long, but the most signficant 2 bytes are not used. See the PWR_CC register description for
more details.
Apparent Power, Phase X = A/B/C/T (PWRS.X) (A: 0x821, B: 0x822, C: 0x824, T: 0x827)
This register contains the apparent instantaneous power delivered into phase A/B/C or total. Power is calculated
from the instantaneous energy measurement according to the following equation:
The register is 8 bytes long, but the most significant 2 bytes are not used. See the PWR_CC register description for
more details.
PWRS X X APP PWR CC
NS
.._
=××216
PWRQ X X REA PWR CC
NS
.._
=××216
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 53
Voltage and Current
RMS Volts, Phase X = A/B/C (V.X) (A: 0x831, B: 0x832, C: 0x834)
This register contains the RMS voltage on phase A/B/C. The units are defined by the VOLT_CC setting such that V.X
= X.VRMS x VOLT_CC. In this equation, VOLT_CC is the conversion coefficient. See the VOLT_CC register for more
information.
RMS Amps, Phase X = A/B/C/N (I.X) (A: 0x841, B: 0x842, C: 0x844, N: 0x840)
This register contains the RMS current on phase A/B/C or the neutral channel. The units are defined by the AMP_CC
setting such that I.X = X.IRMS x AMP_CC. In this equation, AMP_CC is the conversion coefficient. See the AMP_CC
register for more information.
Power Factor
Power Factor (PF.T) (0x867)
This signed register contains the power factor of the total power. The power factor is calculated as:
It is expressed in units of 0.00001; thus, unity power factor is expressed as decimal 100,000
(0x00000000000186A0). This register is presented as a two’s complement value, so that a load delivering real power
to the line (that is, reverse power) is seen as having a power factor of -1 (0x0000FFFFFFFE7960).
PF T A ACT B ACT C ACT
A APP B APP C APP
....
...
=++
++
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
54 ______________________________________________________________________________________
Energy
Real Energy, Phase A/B/C/T (ENRP.X) (A: 0x8C1, B: 0x8C2, C: 0x8C4, T: 0x8C7)
This signed register contains the real accumulated energy delivered into phase A/B/C or total. The register is calcu-
lated according to the following formula:
ENRP.X = ENR_CC x (X.EAPOS - X.EANEG)
Reactive Energy, Phase A/B/C/T (ENRQ.X) (A: 0x8D1, B: 0x8D2, C: 0x8D4, T: 0x8D7)
This signed register contains the reactive accumulated energy delivered into phase A/B/C or total. The register is
calculated according to the following formula:
ENRQ.X = ENR_CC x (X.ERPOS - X.ERNEG)
Apparent Energy, Phase A/B/C/T (ENRS.X) (A: 0x871, B: 0x872, C: 0x874, T: 0x877)
This register contains the apparent accumulated energy delivered into phase A/B/C or total. The register is the prod-
uct of the ENR_CC and X.ES registers.
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 55
Theory of Operation
Analog Front-End Operation
Whenever the MAXQ3180 is in one of the active operat-
ing modes (Run Mode or LOWPM Mode), the analog
front-end operates continuously, scanning up to eight
scan slots depending on the selected front-end config-
uration. For each analog scan slot that is enabled, one
of the eight differential input pairs is measured.
The SCAN_IX and SCAN_VX (X = A/B/C), SCAN_IN,
and SCAN_TE registers contain the settings for each
slot, which include whether the slot is enabled and the
differential input pair to measure during that scan slot.
The logical mapping of the slots is fixed in following
order:
Slot 0—Phase A Current (IA)
Slot 1—Phase A Voltage (VA)
Slot 2—Phase C Current (IC)
Slot 3—Phase C Voltage (VC)
Slot 4—Phase B Current (IB)
Slot 5—Phase B Voltage (VB)
Slot 6—Neutral Current (IN)—disabled by default
Slot 7—Temperature Measurement—disabled by
default
The required time for each analog scan slot measure-
ment (tC) is determined by the MAXQ3180 system
clock frequency and the setting of the R_ADCRATE
hardware register, as shown below:
tC= 1/fCLK x (R_ADCRATE[8:0] + 1)
Using the default register settings (R_ADCRATE = 13Fh
= 319d), the time for each analog slot measurement
(tC) is 40μs when the MAXQ3180 is running at 8MHz.
Since there are eight analog scan slots in the measure-
ment frame, the total time for all measurements (tFR) is
tCx 8. Using the default settings with the MAXQ3180
running at 8MHz, the entire sequence of measurements
takes 320μs to complete, which, in turn, means that
320μs will elapse, for example, between one phase A
current measurement and the next.
Even if some of the analog measurement slots (such as
neutral current or temperature measurement) are
skipped by setting the DADCNV bit in that slot’s regis-
ter to 1, the time period for that slot will remain in the
frame, ensuring that the total frame time is always tCx
8, regardless of which individual slots are enabled or
disabled.
Digital Signal Processing (DSP)
Terminology
Establishing the precise definitions of some of the terms
used in this document will assist in understanding how
the DSP functions.
Sample Period: The amount of time required to mea-
sure a single data element; 40μs, by default.
ADC Frame Period: The amount of time required for
the ADC to sample all analog inputs; always equal to 8
sample periods. The inverse of this value is the
frame
rate
; by default 3125 samples per second. This is the
rate at which any particular signal is sampled by the
MAXQ3180.
Line Cycle: The period of time from one positive-going
zero crossing on a voltage channel to the next positive-
going zero crossing. At 50Hz, this is nominally 20ms; at
60Hz, this is nominally 16.67ms.
Cycle Count: The number of line cycles contained in a
single DSP cycle. An integer, this is typically set to
some value greater than one to minimize the effect of
load variations that may not occur in every line cycle.
By default, this value is 16.
DSP Cycle: The period of time over which line parame-
ters are calculated. Energy and other parameters are
accumulated once per DSP cycle. One DSP cycle is
the time of a line cycle multiplied by the cycle count.
NS: This value represents the number of ADC frame
periods in a DSP cycle. This is a noninteger calculated
value. For example, if the cycle count is set to unity,
and the line frequency is exactly 50Hz, the NS value
would be 20ms/320μs = 62.5.
Digital Processing
As voltage and current samples are collected, the
MAXQ3180 performs a variety of digital filtering,
accumulation, and processing calculations to arrive at
meter-reading values (such as line frequency, RMS
voltage and current, and active and reactive power)
that can then be read by the master. The MAXQ3180
calculates and detects values and conditions including
the following:
Zero-crossing detection
Line frequency and line period calculation
RMS voltage (phase A, phase B, phase C)
RMS current (phase A, phase B, phase C, neutral
current)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
56 ______________________________________________________________________________________
Power (active, reactive, and apparent) for each
phase
Energy accumulation (including energy pulse output
function)
Overvoltage detection
Overcurrent detection
Undervoltage detection
Per Sample Operations
On every ADC frame, the input samples are processed
as follows:
The voltage and current samples are read. The cur-
rent sample is shifted to account for the gain applied
in the PGA. The phase- and gain-corrected samples
are passed to the next stage.
Both the current and voltage signals are passed
through highpass filters (HPF) specified by the
HPF_C variable.
The current and voltage signals are now split into
several components. The first of these components is
squared and accumulated to begin the RMS current
and voltage process. The second is processed and
accumulated to begin the real/reactive power calcu-
lation. And a third is processed through a peak filter
(specified by B0FUND and A1FUND registers) and
then accumulated to provide information for the fun-
damental frequency power calculations.
The result is a set of accumulated values that represent
squared voltage, squared current, and real (active) and
reactive (P and Q) energies for both the entire usable
spectrum and as filtered by the peak filter. The real and
imaginary components of energy at this point do not yet
represent real and reactive power; to obtain usable
power values further processing is required. Each of
these values is further processed at the end of each
DSP cycle.
Per DSP Cycle Operations
At the end of each DSP cycle, accumulated information
is available that is used to calculate all other opera-
tional results in the meter. DSP cycles track the line fre-
quency and have a duration of the number of cycles
specified in the CYCNT register. On each phase, the
time required for CYCNT cycles to complete is calculat-
ed and this value is used to update the duration of one
DSP cycle, specified in the NS register.
NS contains the number of ADC frame periods in a sin-
gle DSP cycle. Because line frequency varies slightly
from cycle to cycle, and because the ADC frame clock
is not synchronized to the line, the value of NS is not an
integer, and varies slightly from DSP cycle to DSP cycle.
Because the value of NS is so critical to accurate calcu-
lation of energy, ensuring that it is correct on every
cycle is essential. There are two ways to manage the
slight variation of NS from cycle to cycle: first, one
could simply replace the old value of NS with the newly
calculated value on each DSP cycle. This means that
NS (and every other value in the meter, since they
depend on NS) would have a significant amount of
uncertainty. A better method is to use each newly cal-
culated value of NS as an input to a filter. The
output
of
the filter is then the value of NS that is actually used in
calculations. In the MAXQ3180, this filter is controlled
by the AVG_NS register.
CURRENT INPUT ADC
HPF
BPF
BPF
EP
I2
EQ
X2
V2
X2
ENERGY PROCESSING
EPF
EQF
ENERGY PROCESSING
VOLTAGE INPUT
HPF
GAIN SEL I_GAIN
V_GAIN
ADC
Figure 9. Per Sample Operations
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 57
A second problem with updating NS on every line
cycles is the fact that noise impulses that occur at near-
ly the same time as the zero crossing can shift the zero
crossing, affecting the accuracy of the energy mea-
sured during the preceding period. For this reason, a
second register, REJ_NS contains a value that specifies
how far a particular sample can deviate from the aver-
age and still be considered valid. If the period of the
newly acquired DSP cycle differs from the previously
accumulated average value by more than REJ_NS ADC
frames, NS is not updated with the new period (but the
energy is still accumulated).
With this discussion in mind, the signal path for the vari-
ous reported parameters can be reviewed.
RMS Volts and RMS Amps: First, the squared voltage
accumulation is divided by NS. This accomplishes the
“mean” part of the “root-mean-square” calculation.
Then, the square root of the result is taken, producing
the raw RMS calculation value.
On the voltage channel, the signal is ready for gain
compensation to be applied. But on the current channel,
there is an additional twist: depending on the amplitude
of the current, there may be a gain factor pre-applied
before the raw sample is available. To compensate for
inaccuracy in the gain factor for the amplifier and for
noise seen in the channel at high gain settings, it may
be necessary to provide linearity compensation.
There are three registers that manage the linearization
of the current signal: the X.OFFS_HI (X = A/B/C) regis-
ter contains a signed value that is added to the raw
RMS current signal before further processing; the
X.OFFS_LO register contains a signed value that is
added to the raw RMS current signal when the current
signal is below a low current threshold (1/32 of the full
scale) value; and the X.GAIN_LO register contains a
gain adjustment that is applied to the current signal
when the current signal is below the threshold value.
The practical effect of this is to turn what may be a
somewhat nonlinear response curve for the current sen-
sor to a much more linear response by two-piece
approximation.
The “high current” calibration term X.OFFS_HI is used
so long as the instantaneous current exceeds the low-
current threshold at some instant during a DSP cycle. As
long as this threshold is crossed during a DSP cycle, the
value in X.OFFS_HI controls the offset current.
When the input stays below the low-current threshold
for one DSP cycle, the X.OFFS_LO and X.GAIN_LO are
applied. The low-current calibration terms (X.GAIN_LO
and X.OFFS_LO) remain in effect until the peak of input
current waveform exceeds 1/32 of full-scale current at
any time during a DSP cycle.
As a final step, both voltage and current are passed
through an averaging filter that provides smoothing for
the signals. The amount of filtering is given in AVG_C.
Energy: The per-sample processing produces a pair of
digital signals that represent the complex energy sig-
nal. From this complex signal, it is desired to extract the
real portion and the reactive portion. At first glance, this
seems trivial: the real portion is the real part of the com-
plex signal, and the reactive portion is the imaginary
part of the complex signal. Apparent power (in volt-
amperes) is the magnitude of the complex signal, and
power angle is the argument of the complex signal.
LINEARIZATION AVERAGE
AVG_C
IRMS
OFFS_HI
GAIN_LO
OFFS_LO
RAW_I
AVERAGE
AVG_C
VRMS
RAW_V
I2
NS
V2
NS
Figure 10. Computation of RMS Values
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
58 ______________________________________________________________________________________
But current sensors and other external circuitry compo-
nents introduce a phase distortion to the current signal,
and this phase distortion may not be constant at all cur-
rent values. Consequently, for the most precise mea-
surements, the phase between the voltage and current
signals must be compensated. In the MAXQ3180, the
energy signals are compensated for phase offset by
performing a complex multiplication of the signal with
the contents of the appropriate phase offset register.
Determining which phase offset register is appropriate is
a matter of comparing the incoming RMS current for the
phase with the contents of the I1THR and I2THR regis-
ters. It is the responsibility of the administrative software
to ensure that I1THR is greater than or equal to I2THR. If
the raw RMS current is greater than or equal to the con-
tents of I1THR, then the angle expressed in PA0 is used
to compensate the phase angle. If the raw RMS current
is less than I2THR, then the angle expressed in PA2 is
used to compensate the phase angle. And if the raw
RMS current falls between I1THR and I2THR then PA1 is
used to compensate the phase angle. In this way, a
three-piece stepwise approximation of the phase
response of the current sensor is available.
To use a constant phase compensation, set I1THR and
I2THR to zero and insert the phase compensation value
into PA0.
The same processing can be performed to calculate
the reactive energy value. But reactive energy can be
calculated in another way: calculate apparent energy
by multiplying the raw RMS volts and raw RMS current,
square this value, then subtract the squared real
power. The square root of this value is the reactive
energy.
Similarly, apparent energy can be calculated in either
of two ways: either as the product of the raw RMS volts
and amps, or as the square root of the sum of the
squares of the real and reactive energy. Which of these
is selected depends on the value of the APPSEL bit in
the OPMODE2 register: if 0, then apparent energy is
the product of the raw RMS volts and amps and reac-
tive energy is calculated using the difference of
squares method; if 1, apparent energy is calculated
using the sum of squares method and reactive energy
is calculated directly from the complex energy.
Line Frequency and Phasor Angles: Line frequency
can be taken directly from the NS value. Recall that NS
is the number of frames in a DSP cycle. Since each
frame is 320μs, simply multiply NS by 320μs and divide
by CYCNT to obtain the line period. The reciprocal of
this is the line frequency.
To calculate phasor angles, the numbers of samples
between zero crossings on phase A and B and on phase
A and C are taken. Since NS is the number of samples
during a complete DSP cycle, it is easy to calculate the
fraction of a complete cycle. The software then converts
this value to degrees and adjusts it such that no negative
angles are reported. No calibration is required for line
frequency and phasor angle calculation.
Energy Accumulation
Once real and reactive energy over the most recent
DSP cycle has been calculated, it is necessary to accu-
mulate the result.
For reactive energy, the result accumulated during any
DSP cycle may be positive (for an inductive load) or
PA
PA I I THR
PA I THR I I THR
PA
RMS
RMS
=
>≥
01
11 2
2
,
,)
,,I I THR
RMS <
2
PHASE
COMPENSATION
PA0
PA1
PA2
EP
EQ
REAL/REACTIVE
PROCESSING
LINEARIZATION AVERAGE
AVG_C
EREAL
OFFS_HI
GAIN_LO
OFFS_LO
LINEARIZATION
OFFS_HI
GAIN_LO
OFFS_LO
E_GAIN
E_RAWREAL
E_RAWREACTIVE
Figure 11. Phase Compensation for Energy Calculations
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 59
AVERAGE
AVG_C
EAPPARENT
E_GAIN
APPSEL
X2 + Y2
E_RAWREAL
E_RAWREACTIVE
X2 - Y2
X × Y
RAW_I
RAW_V
AVERAGE
AVG_C
EREACTIVE
E_GAIN
APPSEL
Figure 12. Apparent and Reactive Energy Calculations
negative (for a capacitive load). These values are sepa-
rately accumulated. This means that during any one
DSP cycle, only positive or negative reactive energy will
be accumulated.
Similarly, for real energy, the result accumulated during
any DSP cycle can be positive (that is, energy is deliv-
ered to the load) or negative (that is, energy is driven
back into the line). As is performed for reactive energy,
these values are separately accumulated.
Apparent energy is also accumulated, but since this
value is always positive or zero, there is only one
apparent energy accumulator.
From time to time, the accumulators generate an over-
flow. When this occurs, the appropriate bit is set in the
overflow status register X.EOVER.
When an overflow occurs, supervisory code running on
the host processor must make the appropriate adjust-
ments in the reported energy. In many cases, this could
simply involve incrementing an overflow counter. The
host processor must then clear the overflow indication.
No-Zero-Crossing Detection
The MAXQ3180 monitors the voltage signal on each
phase for zero-crossing events. If no ascending zero
crossings are detected within a specified number
(NZX_TIMO) of analog scan sample periods, the
NOZXF (X.FLAGS) flag is set by the MAXQ3180 to noti-
fy the master of this condition. If the NOZXM bit is set,
this flag sets the NOZX bit in the IRQ_FLAG. If the inter-
rupt enable bit ENOZX is set to 1, the interrupt signal
IRQ is driven low by the MAXQ3180 whenever NOZX =
1. The master can clear NOZXF and NOZX back to 0 to
remove the interrupt condition.
Phase Sequence Status
A phase sequence status bit PHSEQ indicates the
order in which zero crossings are detected. When a
zero-crossing event occurs on the phase A voltage sig-
nal, followed by phase B, phase C, and then phase A
again, this bit cleared. If a zero crossing on phase A is
then followed by a zero crossing on phase C, then
phase B, this bit set to 1.
RMS Voltage, RMS Current, and Energy
Calculation
For each of the three phases, the MAXQ3180 calcu-
lates RMS voltage and RMS current values, as well as
determines active and reactive energy, using a line-
cycle-based integration process.
Power Calculation (Active, Reactive,
Apparent)
The power, energy, and RMS calculation process con-
sists of two tasks: continuous accumulation and post-
processing triggered every CYCNT line cycles. The
accumulation task accumulates raw data obtained from
the AFE during CYCNT line cycles. This task is per-
formed continuously in the background by the
MAXQ3180. When a CYCNT line cycles accumulation
stage has completed, which is determined by a dedi-
cated frame counter exceeding the NS level, the raw
integral accumulator values are saved for postprocess-
ing and cleared, beginning the next cycle of accumula-
tion task. Then, the DSP postprocessing is triggered to
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
60 ______________________________________________________________________________________
process saved integrals and calculate energy, power,
etc., values. Note that the background accumulation
task continues while foreground postprocessing is tak-
ing place, i.e., both tasks are executed simultaneously
sharing CPU time. It is essential that the DSP postpro-
cessing calculations be completed before the next DSP
trigger to avoid losing accumulated data. The master
should allow enough processing time by adjusting the
R_ADCRATE register. Default settings provide plenty of
CPU time for both tasks.
The MAXQ3180 accumulates raw sums and calculates
line-cycle integrals for each voltage-current pair sepa-
rately. The individual power accumulators are:
PA = VAx IA
PB = IBx VBor -IBx VCor -IBx (VA+ VC) or -IBx
(VA- VC)
PC = VCx IC
The PA and PC accumulators always operate in a sin-
gle mode: (VAx IA) for the PA accumulator, (VCx IC) for
the PC accumulator. Alternately, the operating mode of
the PB accumulator is defined by setting the
CONCFG[1:0] bits in the OPMODE1 register.
Energy Accumulation Start Delay
All filters have a certain settling time before accurate
energy readings can be accumulated. To avoid accu-
mulation of invalid data from filters that are still settling,
an energy accumulation timeout period can be set in
the ACC_TIMO register. When ACC_TIMO > 0, comput-
ed energy is not accumulated for ACC_TIMO of DSP
cycles. The MAXQ3180 will decrement the ACC_TIMO
register every DSP cycle until it becomes 0. When
ACC_TIMO reaches 0 value, energy accumulation
begins (or resumes, if ACC_TIMO was set to nonzero
value by the master). Pulse outputs are also disabled
when ACC_TIMO > 0. The default value of ACC_TIMO
is 0x05.
No-Load Feature
To avoid “meter creep,” no energy accumulation should
take place when measured current is less than a cer-
tain threshold. The NOLOAD register can be pro-
grammed to enable and configure this feature. If the
measured X.IRMS value for a phase (A, B, or C) falls
below the NOLOAD threshold, the energy accumulators
for this phase are not incremented. Setting NOLOAD =
0 disables this feature. Full scale is represented by
0x10000.
On Demand Calculations
So far in this discussion, the values being calculated
and managed in the MAXQ3180 have been based on
fundamental units meaningful to the device itself: volt-
age as a binary fraction of full-scale voltage; current as
a binary fraction of full-scale current, and time as a non-
integer multiple of the ADC frame time.
But a practical electricity meter must report its results in
standard units, such as volts, amperes, and watts. The
MAXQ3180 contains a mechanism to convert the inter-
nal units (“meter units”) to real world units (“display
units”). This conversion is performed in the conversion
constant (CC) registers.
For some of these values (voltage, current) the calcula-
tion is simple: multiply by the conversion constant. For
other values (power, energy) the calculation is more
complex. In any case, the value in the CC register
affects only the conversion from a meter unit to a dis-
play unit; calibration is handled separately in the gain
adjustment registers for each recorded value.
The results of all on-demand calculations are reported
as 8-byte (64-bit) values of which no more than 6 bytes
(48 bits) are significant. Eight bytes are used as a com-
mon length; however, fewer bytes can be requested for
those registers known to have smaller maximum values.
For example, the power factor virtual register has a
maximum value that is expressed in only 3 bytes; con-
sequently, the register can be requested with a length
of 4 bytes without loss of data.
RMS Volts, RMS Amps
These registers (V.A, V.B, V.C, I.A, I.B, I.C) are calculat-
ed by simply multiplying the calculated RMS value
(A.VRMS, B.VRMS, C.VRMS, A.IRMS, B.IRMS, C.IRMS)
by the contents of the VOLT_CC or AMP_CC register.
Since the RMS voltage and RMS current are given in
32-bit registers and the conversion coefficients are
given in 16-bit registers, the result of the product is 48
bits.
Regardless of the internal units used, VOLT_CC and
AMP_CC can be tailored so that the LSB of the virtual
register can be any value. For example, if one wished
to have a 32-bit value representing milliamps, one
could multiply by a value that scaled the register such
that the LSB was 2-16mA. Then, discard the low-order
16 bits. The result is milliamps with 32 bits of precision;
thus, the maximum current that could be represented
would be 4,294,967,296mA, or just over 4MA.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 61
The VOLT_CC and AMP_CC values can be calculated
from the full-scale voltage or full-scale current and the
desired value of one LSB in the display register:
Example: Assume the full-scale current is 102.4A, and
that we desire a 1nA LSB. The calculation would pro-
vide an AMP_CC value of:
102.4/(224 x 10-9) = 6104 = 0x17D8
Power
The MAXQ3180 measures energy. But power is just
energy per unit time, and the MAXQ3180 keeps track of
the time unit over which energy is accumulated. This is
simply the NS value, the fractional number of samples
that comprises one DSP cycle. So converting energy to
power is as simple as dividing the accumulated energy
over one DSP cycle by NS. Multiplying by a conversion
constant (PWR_CC) gives power in user-established
units.
The power registers (PWRP.A, PWRP.B, PWRP.C,
PWRQ.A, PWRQ.B, PWRQ.C, PWRS.A, PWRS.B,
PWRS.C) are calculated by multiplying the accumulat-
ed energy (A.ACT, A.REA, A.APP, B.ACT, B.REA,
B.APP, C.ACT, C.REA, C.APP) by the conversion coeffi-
cient (PWR_CC) and then dividing by NS. The result is
the 48-bit average power over the most recent DSP
cycle, in units established by the conversion coefficient.
The PWR_CC value can be calculated from the full-
scale voltage, the full-scale current, and the desired
value of one LSB in the display register:
Example: For this example, assume the full-scale cur-
rent is 102.4A, the full-scale voltage is 558.1V, and that
the desired LSB is milliwatts after discarding the 16
LSB; that is, the desired LSB is 2-16 milliwatts. Perform
the following calculation:
102.4 x 558.1/(232 x 2-16 x 10-3) = 872 = 0x0368
Power Factor
Power factor is calculated as real power divided by
apparent power. But note that apparent power can be
calculated in either of two ways: either as a square root
of the sum of the squares of the real and reactive
power, or more commonly as the product of the RMS
voltage and current measurement. The power factor as
reported could change when one or the other of these
methods is used.
The power factor is multiplied by 214 before it is report-
ed; thus, unity power factor is given by 16,384 decimal
(0x4000).
Line Frequency
The line frequency is derived directly from the mean NS
values over the three phases. It is reported as millihertz;
thus, a 50Hz line frequency is reported as decimal
50,000 (0xC350).
Phasor Angles
The phasor angles are taken directly from the angular
measurement values determined at each DSP cycle.
The angle is reported in units of 0.01 degree; thus, a
120° phasor is reported as decimal 12,000 (0x2EE0).
Energy
Energy is read as the net energy directly scaled from
the appropriate registers. For example, the energy read
from the ENRP.A register (real energy, phase A) is
composed of the difference between the A.EAPOS (real
energy, positive direction, phase A) and A.EANEG (real
energy, negative direction, phase A) registers scaled
by the ENR_CC register.
Note that the energy registers (ENRP.A, ENRP.B,
ENRP.C, ENRP.T, ENRQ.A, ENRQ.B, ENRQ.C, ENRQ.T,
ENRS.A, ENRS.B, ENRS.C, ENRS.T) represent the ener-
gy, in every case, since the last overflow event. For this
reason, software must keep track of overflow and make
adjustments accordingly when using this register set.
To calculate the ENR_CC register value, begin with the
full-scale voltage and full-scale current, the frame time,
and the desired LSB value for energy. Then perform the
following calculation:
Example: It is essential to ensure that the correct units
are maintained throughout the calculation. In this exam-
ple, assume that the full-scale voltage is 558.1V, the
full-scale current is 102.4A, the frame time is the default
of 320μs, and the desired LSB is 100 milliwatt-hours
after the 32 bits are discarded; that is, the LSB is 0.1 x
2-32 watt-hours. Notice, however, that the frame time is
given in microseconds
and must be converted to hours
before the calculation can be performed: 320μs is 88.9
x 10-9 hours. So the calculation proceeds as follows:
102.4 x 558.1 x 88.9 x 10-9/(216 x 0.1 x 2-32) = 3329 =
0x0D01
ENR CC IVt
ENR LSB
FS FS FR
__
=××
×216
PWR CC IV
PWR LSB
FS FS
__
=×
×232
VOLT CC V
VOLT LSB
FS
__
=×224
AMP CC I
AMP LSB
FS
__
=×224
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
62 ______________________________________________________________________________________
Meter Pulse
The purpose of a meter pulse is generally to advance a
mechanical counter when such a device is used as a
display. Meter pulses are also used during calibration
since time intervals can be measured with great preci-
sion.
The MAXQ3180 supports two meter pulse outputs.
These outputs can be configured for either active posi-
tive or active negative pulses by means of the POPOL
bit in the OPMODE1 register. When triggered, the pulse
goes to its active state and remains there for a period of
time defined by the PLS1_WD or PLS2_WD register,
and then returns to the inactive state (unless triggered
again).
The PLS1_WD and PLS2_WD registers contain the time
in ADC frame periods that the pulses remain in the
active state when triggered. By default, these registers
contain decimal 156 (0x9C) giving, at the default frame
rate, a pulse width of 50ms.
Each pulse generator can select one parameter to be
accumulated over any combination of the three phases.
For example, one could select real energy accumulated
over all three phases for pulse output 1, and reactive
energy accumulated over all three phases for pulse
output 2. The particular parameters that can be accu-
mulated are given in the register table.
Among the quantities that can be accumulated by the
pulse subsystem are the arithmetic active energy (that
is, the accumulated positive real energy minus the
accumulated negative real energy) and the absolute
active energy (that is, accumulated positive real ener-
gy plus accumulated negative real energy). Other
quantities include RMS voltage and current, positive
and negative real energy and reactive energy in each
of the four quadrants. Select the desired accumulation
value in the QNSEL field of the PLSCFG1 and
PLSCFG2 register.
Also in the pulse configuration registers you can select
which phases to include in the accumulation. Set any or
all the PHASEA, PHASEB, and PHASEC bits in the
PLSCFG1 or PLSCFG2 registers to include them in the
accumulation.
Generating Pulses
On every DSP cycle, the MAXQ3180 adds the value in
the selected register (or set of registers) to the pulse
accumulator. If the value in the pulse accumulator
exceeds the value in the associated threshold register
(THR1 or THR2), then a pulse is started and the value in
the threshold register is subtracted from the value in the
pulse accumulator.
Meter Constant
A meter constant is the number of pulses that are gen-
erated during a standard measurement interval; for
example, a meter might specify a meter constant of
1600 pulses per kilowatt-hour. The THR1 and THR2
registers are used to specify the meter constant
according to the following formula:
In this formula, THR is the value to be written to the
threshold register, KMis the desired meter constant (in
pulses per kilowatt hour), IFS and VFS are the full-scale
voltage and current, respectively, and tFR is the frame
period in units of hours, as in the previous calculation.
As an example, assume once again a full-scale voltage
value of 558.1V = 0.5581kV, a full-scale current value of
102.4A, a desired meter constant of 1600 pulses per
kilowatt hour, and a default frame time of 320μs (88.9 x
10-9 hours). The threshold register value can be calcu-
lated as:
65,536/(1600 x 102.4 x 0.5581 x 88.9 x 10-9) =
8,063,071 = 0x7B085F
Increasing the value of the threshold register
reduces
the meter constant (that is, there are fewer pulses per
kilowatt-hour); reducing the threshold register
increases
the meter constant (that is, there are more pulses per
kilowatt-hour.)
Interrupts
The MAXQ3180 contains an interrupt subsystem to
relieve the host processor of the burden of constantly
polling the device for status. Instead, under certain cir-
cumstances, the MAXQ3180 can activate an external
pin to alert the host processor that some condition
requiring host attention has occurred.
Interrupts are managed globally by the IRQ_MASK and
IRQ_FLAG registers. In general, when a bit becomes
set in the IRQ_FLAG register, an interrupt is generated
if the corresponding bit is set in the IRQ_MASK register.
Interrupts can be configured for the following conditions:
PWRF: This flag indicates the VDVDD to the
MAXQ3180 has fallen below its nominal operating
threshold (about 2.85V). This can be taken as an
indication that power failure is imminent and that the
host processor should begin taking steps to ensure
an orderly shutdown.
CHSCH: This flag indicates that the CHKSUM regis-
ter changed its value.
THR KI V t
MFS FS FR
=×× ×
216
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 63
EOVF: Energy overflow. This flag indicates that one or
more energy accumulators (X.EAPOS, X.EANEG, etc.)
have overflowed. In a traditional meter, the host
processor would poll the MAXQ3180 to determine
which of the energy accumulators have overflowed and
adjust its internal accounting registers accordingly.
OC: The RMS current value on one or more of the
phases over the most recent DSP cycle has exceed-
ed the value set in the OCLVL register.
OV: The RMS voltage on one or more of the phases
over the most recent DSP cycle has exceeded the
value set in the OVLVL register.
UV: The RMS voltage on one or more of the phases
over the most recent DSP cycle has failed to exceed
the value set in the UVLVL register.
NOZX: Zero crossings were not detected on one or
more of the phases. The detection time is defined in
the NZX_TIMO register. The resolution for the
NZX_TIMO register is the duration of one ADC sam-
ple time (nominally 40μs).
DCHA: Tells the host processor that the direction of
net real energy flow on one of the three phases has
changed during the current DSP cycle as compared
to the previous DSP cycle.
DCHR: Tells the host processor that the direction of
net reactive energy flow on one of the three phases
has changed during the current DSP cycle as com-
pared to the previous DSP cycle.
DSPRDY: Indicates the latest DSP cycle has just
completed.
DSPOR: Indicates that the processing for the previ-
ous DSP cycle had not been completed before the
current DSP cycle became available for processing.
This overflow indication should never be seen in the
default configuration; however, under some condi-
tions (faster ADC rate, slower CPU clock) the pro-
cessing requirements may exceed the number of
CPU cycles available for DSP processing. Under
these circumstances, the clock rate may be
increased, the ADC rate may be reduced (that is,
the R_ADCRATE register may be increased), or the
functional load (such as fundamental mode calcula-
tions) may be cut.
Note that when DSPOR becomes set, all DSP calcu-
lations as well as all pulse outputs are invalidated.
The appropriate host response is to take the remedi-
al action described above and discard the current
set of DSP result values.
Each phase has a local register that contains copies of
the OC, OV, UV, NOZX, DCHA, and DCHR bits. Thus,
to determine which phase(s) have exception conditions
requires four reads: the IRQ_FLAG register to deter-
mine which conditions are active that are causing the
interrupt to occur, and then a read to A.FLAGS,
B.FLAGS, and C.FLAGS to determine which of the
phases have the indicated condition.
Finally, each phase has a pair of local registers that
contain overflow flags for each energy accumulator. If
the EOVF bit is set in the IRQ_FLAG register, the host
should then read the A.EOVER, B.EOVER, and
C.EOVER registers to determine which of the phases
have overflow conditions. If fundamental mode opera-
tion is enabled, the host should read A.EFOVER,
B.EFOVER, and C.EFOVER as well. Each of these reg-
isters contains a bit for each of real and reactive energy
in both positive and negative direction as well as
apparent energy.
Overvoltage and Overcurrent Detection
The MAXQ3180 detects overvoltage and overcurrent
events and can issue interrupt request signals to the
master when these events occur. The overvoltage level
can be programmed into the OVLVL register, while the
overcurrent level is determined by the OCLVL register.
Both OVLVL and OCLVL registers represent the bits
23:8 of the VRMS or IRMS registers. Any time the
MAXQ3180 detects the RMS-value exceeding a thresh-
old level, the OV or OC interrupt flag is set. If enabled,
any of these flags issues an interrupt request. All inter-
rupt flags are “sticky” bits—the MAXQ3180 never
clears them on its own unless a reset occurs. The inter-
rupt flags should be cleared by the master by writing
the appropriate register.
Meter Units to Real Units Conversion
All energy calculations, including various threshold
checks, are performed internally in fixed format in meter
units. Therefore, the threshold values must be supplied
by the user in meter units as well. This section summa-
rizes how to convert real units (V, A, kWh, W, and kAh)
into meter units and vice versa.
The conversion factors are based on the settings of tFR,
VFS, and IFS, defined by the user’s design.
tFR is analog scan frame timing. This parameter is
defined by the R_ADCRATE setting and system clock
frequency fSYS:
tFR = (R_ADCRATE + 1) x 8/fSYS
Default conditions are R_ADCRATE = 319, fSYS = 8MHz.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
64 ______________________________________________________________________________________
VFS is full-scale voltage. This is the input voltage that
produces full-scale ADC output; defined by the hard-
ware voltage transducer ratio VTR and ADC full-scale
input voltage VFSADC:
VFS = VFSADC x VTR
Default conditions are VFSADC = 1.024V. VTR is design
dependent.
IFS is full-scale current. This is the input current that
produces full-scale ADC output; defined by the hard-
ware current transducer ratio ITR and ADC full-scale
input voltage VFSADC:
IFS = VFSADC x ITR
Default conditions are VFSADC = 1.024V. ITR is design
dependent.
Meter units are defined with respect to the base para-
meters as shown in Table 5.
When reading virtual registers, the MAXQ3180 uses the
configurable conversion coefficients AMP_CC,
VOLT_CC, PWR_CC, and ENR_CC to return meaningful
data. Table 6 describes how to set the coefficients.
Table 6. Virtual Register Coefficients
VIRTUAL REGISTER OUTPUT RESOLUTION
(1 LSB), DEFINED BY USER COEFFICIENT
Power:
PWRP.X, PWRQ.X, PWRS.X, PWRPF.X,
PWRQF.X, PWRSF.X
PWR_LSB PWR_CC = MU_PWR/PWR_LSB
Voltage:
V.X VOLT_LSB VOLT_CC = MU_VOLT/VOLT_LSB
Current:
I.X AMP_LSB AMP_CC = MU_AMP/AMP_LSB
Energy:
ENRP.X, ENRQ.X, ENRS.X, ENRPF.X,
ENRQF.X, ENRSF.X
ENR_LSB ENR_CC = MU_ENR/ENR_LSB
REGISTER OR ACCUMULATOR METER UNIT (1 LSB)
Current RMS: X.IRMS
Pulse output current RMS
THR1 or THR2, when pulse output configured to IRMS
MU_AMP = IFS/224
Voltage RMS: X.VRMS
Pulse output RMS voltage
THR1, or THR2 when pulse output configured to VRMS
MU_VOLT = VFS/224
Energy: X.ACT, X.REA, X.APP, X.EAPOS, X.EANEG, X.ERPOS,
X.ERNEG, X.ES
Fundamental Energy: X.ACTF, X.REAF, X.APPF, X.EAFPOS,
X.EAFNEG, X.ERFPOS, X.ERFNEG, X.ESF
Pulse Output Energy: THR1 or THR2
MU_ENR = VFS x IFS x tFR/216
Power: PWRP.X, PWRQ.X, PWRS.X MU_PWR = VFS x IFS/232
When X.ESF Contains Amp-Hours: X.ESF MU_AH = IFS x tFR/216
OCLVL, NOLOAD, I1THR, I2THR IFS/216
OVLVL, UVLVL VFS/216
Table 5. Meter Unit Definitions
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 65
Units Conversion Examples
The conversions from meter units to physical units are
illustrated with the simplified input circuits in Figures 13
and 14. The voltage input circuit is a voltage-divider.
Current input is through a current transfer with turn ratio
of 2000:1.
The voltage transducer ratio (VTR) = (R1 + R2)/R2 =
545, VFS = 558.1V.
The current transducer ratio (ITR) = CT_N/(2 x R) =
2000/(2 x 10) =100 (A/V), IFS = 102.4A.
The input circuits should be designed to avoid getting
too close to the ADC input full sale at the specified
maximum ratings. So for the above circuits, we would
specify the maximum input current = 70A (RMS) and
maximum voltage = 390V (RMS), to ensure that peak of
sinusoudal waveform never exceeds IFS or VFS.
Use the default ADC timing tFR = 320μs, we get the fol-
lowing meter unit to physical unit conversion coeffi-
cients (these coefficients are not part of the MAXQ3180
registers):
MU_AMP = IFS/224 = 6.1E-6 (A)
MU_VOLT = VFS/224 = 33.3E-6 (V)
MU_PWR = VFS x IFS/232 = 13.3E-6 (W)
MU_ENR = VFS x IFS x tFR/216 = 77.5E-9 (Wh)
For example, if we get 0x07654AF0 from reading
0x1CC register (phase A current RMS), the current
value it represents is
0x07654AF0 x MU_AMP = 47.33 (A)
For some low-end host microcontrollers, doing the
above math multiplication above could be difficult. For
this reason, the MAXQ3180 provides conversions for
some commonly needed parameters through the
VOLT_CC, AMP_CC, PWR_CC, and ENR_CC registers.
For example, if you want to display current in the reso-
lution of 1mA, without having to use a multiplication
operation to convert from the meter unit value
0x07654AF0, you would set AMP_CC to 0x0190, and
read from virtual register 0x831 (phase A RMS current).
The output would be 0xB8E45170. Dropping the lower
2 bytes (right shifting 16 bits) gives 0xB8E4, or 47332
decimal (47332mA).
AMP_CC is computed as follows:
AMP_CC = (IFS/224)/AMP_LSB = MU_AMP/AMP_LSB
AMP_LSB = 0.001/216 (A)
IFS = 102.4A
AMP_CC = (102.4/224)/(0.001/216) = 400d = 0x0190
Calibration Procedure
Calibration Overview
Calibration ensures that the recorded voltage, current,
energy, and power are in accordance with the design
criteria. Before creating a calibration regimen, establish
the fundamental units of the meter: the full-scale volt-
age and current. Then adjust the gain registers using
calculated calibration constants to produce the expect-
ed reading in the raw current, voltage, energy, and
power factor registers.
The calibration constants should be stored in non-
volatile memory by the host microcontroller. Upon any
reset or loss of power, the host microcontroller must
reload the MAXQ3180 with the constants.
Calibration always follows a set of fundamental steps:
Apply a known signal (voltage/current/power) to the
meter.
Read the meter.
Calculate the correction factor based on the differ-
ence between the applied signal level and the meter
reading.
Write the correction factor to the appropriate register.
MAXQ3180
I0P
VCOMM
IA (AC)
I0N
R
10Ω
R
10Ω
Figure 14. Sample Current Input Circuit
MAXQ3180
VOPVA (AC)
VN
R2
1kΩ
R1
544kΩ
Figure 13. Sample Voltage Input Circuit
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
66 ______________________________________________________________________________________
Read the meter quantity again to verify the calibra-
tion.
Note that these steps can occur more than once for a
given signal type to verify readings at different signal
levels.
There are two methods to read the meter in the above
second step. The first is to read the raw register associ-
ated with the value under calibration, for example,
A.VRMS for the phase A voltage channel; A.IRMS for
the phase A current channel, and A.ACT for phase A
real power.
The second calibration method assigns a pulse output
to the value being calibrated and measures the pulse
period. In practical use, the method chosen depends
on the specific application and the available equip-
ment. For example, in some applications the voltage
and current are of no concern, but the energy accumu-
lation must be very accurate. For these applications,
meter calibration sets with built-in pulse measurement
facilities can make the most sense.
The calibration procedure involves the following gener-
al steps:
Calibrate voltage for a given phase by applying a
known voltage and adjusting the voltage gain
(A.V_GAIN for phase A) until the RMS voltage
(A.VRMS for phase A) reads the applied voltage in
the designated units.
Calibrate current by applying a known current and
adjusting the current gain (A.I_GAIN for phase A)
until the RMS current (A.IRMS for phase A) reads the
applied current in the designated units. If desired,
the current can be calibrated at two points (low
range and high range) for more accuracy.
Once the current gain and voltage gain are calibrat-
ed, the power/energy should not require any addi-
tional adjustment for most situations. Although, a
separate power gain register is available for further
fine-tuning of the power/energy accuracy. One must
keep in mind that anytime voltage or current is recali-
brated, the power or energy accuracy is naturally
affected. So the power gain should be recalibrated to
achieve the desired accumulative effect of voltage,
current, and power gains.
Calibrate the phase offset by applying a power factor
load and adjusting the phase angle offset according-
ly. If desired, the phase offset can be calibrated at
up to three points for more accuracy.
Once these elements are calibrated for each phase, all
other information (power factor, reactive power, appar-
ent power, etc.)is also properly calibrated. The descrip-
tions in the following sections deal specifically with
phase A, but the same procedure is followed with phas-
es B and C.
Calibrating Voltage
Ensure that there is no previous value in the gain regis-
ter, A.V_GAIN, by setting this register to 0x4000.
Apply a known voltage with RMS value close to the
desired maximum operating voltage (and less than
VFS/2).
Read the A.VRMS register. Note the value.
Convert the known value to meter units by dividing it
by MU_VOLT (= VFS/224).
Divide the applied value (in meter unit) by the value
read from the MAXQ3180. The result should be a
value between 0 and 2. If the value falls outside of
this range, you have probably miscalculated VFS.
Multiply the calculated value by 214. The result is the
gain value to be programmed into A.V_GAIN. Ensure
the most significant bit is 0.
When the gain value is programmed, wait for 2 to 3
seconds, reread the RMS value from A.VRMS. Check
that the measured value is correct by comparing
A.VRMS against the applied voltage in meter unit.
Voltage Calibration Example
Assumptions: VFS is 558.1V. The applied voltage is 240
VRMS.
Convert the applied voltage to meter units. This cal-
culation gives 240 x 224/558.1 = 7,214,714 =
0x006E1679.
Read the A.VRMS register. You read 0x0708029.
This is 7,372,841 decimal.
Divide the applied voltage by the voltage read from
the meter. The result is 7,214,714/7,372,841 =
0.97855.
Convert to integer by multiplying 214: 16,384 x
0.97855 = 16,033 = 0x3EA1. Write this value to the
A.V_GAIN register.
Calibrating Current
Ensure that there is no previous value in the gain regis-
ter, A.I_GAIN, by setting this register to 0x4000.
Apply a known current with RMS value close to the
desired maximum operating current (and much lower
than IFS/2).
Read the A.IRMS register. Note the value.
Convert the known value to meter units by dividing it
by MU_AMP (= IFS/224).
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 67
Divide the applied value (in meter unit) by the value
read from the MAXQ3180. The result should be a
value between 0 and 2. If the value falls outside of
this range, you have probably miscalculated IFS.
Multiply the calculated value by 214. The result is the
gain value to be programmed into A.I_GAIN. Ensure
the most significant bit is 0.
When the gain value is programmed, wait for approxi-
mately 2 to 3 seconds, then reread the RMS value from
A.IRMS. Check that the measured value is correct by
comparing A.IRMS against the applied current in meter
unit.
Current Calibration Example
Assume IFS is 102.4A and the meter has a base current
of 10A and a maximum current of 60A.
The meter is calibrated at the base current of 10A.
Convert the applied current to meter units. This cal-
culation gives 10 x 224/102.4 = 1,638,400 =
0x00190000.
Read the A.IRMS register. You read 0x0017DC85.
This is 1,563,781 decimal.
Divide the applied current by the current read from the
meter. The result is 1,638,400/1,563,781 = 1.0477.
Multiply by 214 x 1.0477 = 17,166 = 0x430E. Write
this value to the A.I_GAIN register.
Calibrating Phase Offset
For this calibration step, it is necessary to have a power
factor meter, capable of measuring phase angle, con-
nected in the same circuit as the MAXQ3180 meter.
Note that calibration can be performed at any precision
power factor setting. We use a pure resistive load (PF =
1.0) load to illustrate the procedure.
Apply a resistive load to the meter; the current drawn
by the load should correspond to the base current of
your meter.
Record the phase angle and direction (capacitive or
inductive) reported on the power factor meter.
Read and record the real and reactive energy from
the X.ACT and X.REA registers. Divide the reactive
energy by the real energy. This is the tangent of the
power-phase angle.
Read the X.REA register. If the high-order bit is set,
the power factor reported in the above step is capac-
itive. If the high-order bit is clear, the power factor
reported in the above step is inductive.
Now determine the correction factor: treating capaci-
tive values as negative and inductive values as posi-
tive, subtract the angle read from the MAXQ3180
from the angle read from the reference meter. The
result is the compensation angle.
Multiply the compensation angle (in radians) by
65,536. This is the value to write into X.PA0.
If I1THR and I2THR are left at their default values
(0x0000), then the value in X.PA0 is applied to the full
measurement range. Alternatively, you could write the
same value into X.PA0, X.PA1, and X.PA2. Then the
same compensation is applied through the whole mea-
surement range regardless of the I1THR and I2THR set-
tings. If desired, calibrate for the phase angle at up to
three different current levels to compensate for nonlin-
earity in the current sensor. See the
Advanced
Operation
section for more information.
Phase Offset Calibration Example
Assume the meter is a 10/60 meter; that is, the base
current is 10A and the maximum rated current is 60A.
IFS is 102.4A and VFS is 558.1V. The test point is 10A
and 240V.
Connect the MAXQ3180-based meter under test in
series with a lab grade reference meter. See the con-
figuration below.
Apply power to the meter and apply a load of 10A
resistive.
Verify that the I1THR, I2THR, A.PA0, A.PA1, and
A.PA2 registers contain zero.
Read the power factor on the reference meter. You
read 1.5° capacitive. This is not unusual. The load
might not be truly resistive or reactance in the test
configuration could be reflected in the measurement.
Read the real energy from register A.ACT (0x1D0).
You read 0x2865D6 (2,646,510 meter units).
Read the reactive energy from register A.REA
(0x1D4). You read 0xFFFFA5C0 (-23,104 meter
units).
Divide the reactive by the active power: -23,104/
2,646,510 = -0.009.
V
LAB
METER
V
UNIT
UNDER
TEST
LOAD
LINE
NEUTRAL
Figure 15. Offset Testing Setup
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
68 ______________________________________________________________________________________
Take the inverse tangent of this value. You get -0.5°;
that is, 0.5°capacitive.
Subtract the UUT phase offset from the reference
meter phase offset. In this case, the phase needs to
move 1°toward the capacitive. Convert this value to
radians: 1°x π/180°= 0.0175 radians.
Multiply this value by 65,536. The result is 572
(0x023C).
Because the phase correction is toward the capaci-
tive, the value must be complemented. The two’s
complement of 0x023C is 0xFDC4. This is the value
that should be written to the PA0 phase compensa-
tion register.
At this point, the meter is compensated for a single
phase offset. If the phase offset were perfectly flat over
all current levels, that would be sufficient (and for many
current sensors, particularly current shunts, one point is
usually good enough.)
Interfacing the MAXQ3180 to
External Hardware
The MAXQ3180 has all the internal circuitry that is
needed for a sophisticated electricity meter, but specif-
ic external hardware is required when configuring the
meter for a particular application. The most critical
decision that must be made is how the load will be con-
nected to the power source, and how the meter will be
connected to measure power consumed in the load.
This section covers how to select hardware compo-
nents for a MAXQ3180 electricity meter.
Connections to the Power Source
Generally, three-phase power as delivered from the util-
ity consists of four wires: three voltage phases and a
neutral wire. In one typical three-phase delivery system,
measuring from neutral to any phase would read 120V,
while measuring from any phase to any other phase
would read 208V. Connecting a load so that load cur-
rent is taken from phase lines and returned to neutral is
called a wye-connected load. Connecting a load so
that load current is provided by one phase and
returned on another phase is called a delta-connected
load. The MAXQ3180 can measure power consumed in
either a wye-connected or a delta-connected load.
If the load is connected in a wye fashion, the voltage is
measured from the neutral lead to each of the phases,
and the current measuring device is placed in series
with the load, most often in the hot lead. The sensor is
not placed in the neutral lead to prevent a customer
from defrauding the utility by returning the current to
ground rather than neutral. A current sensor placed in
the hot lead makes fraud even more difficult.
A delta-connected load can have current measured in
two possible ways. If it is primarily desirable to know
how much power is delivered to the load, one can place
the current sensor in the load circuit between two phas-
es. But if it is more important to know how much current
is being drawn from each supply phase, each current
sensor is placed in the line circuit of each single phase.
Most utilities are only concerned with the total amount
of energy being consumed. If individually accounting
for the power delivered by each phase is not a require-
ment, it is not necessary to measure all three voltages.
Instead, knowing only two voltages and the three cur-
rents is all that is necessary to measure total energy
usage.
There are several ways of doing this. In a wye arrange-
ment, one of the phases—usually phase B—–can be
considered the voltage reference point instead of neu-
tral. Then the voltage measurements can be made from
phase A to phase B and from phase C to phase B. By
using some simple arithmetic, the power delivered by
phase A, phase B, and phase C can be calculated
even though only two voltages are available.
A second mechanism is to have a delta-connected
load, but with one leg—usually the BC leg—split into
two equal loads. The point where the load is split is
defined as the reference. In this arrangement, it is only
necessary to know the voltage between phase C and
the split and phase A and the split, since VC= -VA.
Finally, there is the connection arrangement in which
the load is in a delta configuration with the current sen-
sor at each load, but it is still desired to determine how
much current is in each supply branch. The MAXQ3180
supports all of these connection arrangements.
Sensor Selection
The MAXQ3180 supports a variety of voltage and cur-
rent sense elements. This section describes the proper-
ties of many of these sensing devices.
Voltage Sensors
Voltage-Divider
A voltage-divider is an ideal voltage-sensing element
when there is no need for voltage isolation. Modern
resistors have virtually no parasitic capacitance or
inductance at the frequencies of interest in an electrici-
ty meter and have extremely low variation with tempera-
ture. When selecting resistors for a voltage-divider,
keep the division ratio high enough so that the peak
voltage value cannot exceed the maximum allowable
input voltage. In the MAXQ3180, the peak input voltage
is about 1V; consequently, a divider in the range of
400:1 to 600:1 is ideal.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 69
The second consideration is the total power dissipation
and voltage hold-off requirements of the resistor. It is
tempting to design a 400:1 divider with a 400kΩresis-
tor in series with a 1kΩresistor, but that would force the
400kΩresistor to dissipate about 140mW. This is not an
excessive amount of power, but if the design is to use
small SMT parts, it can handle greater than a 1/10W
SMT resistor. It is better to use a series of several small-
er components to improve system reliability.
Voltage Transformer
If isolation is required between the meter electronics
and the line, a voltage transformer is required. A volt-
age transformer is designed to faithfully transfer an AC
voltage applied on the primary side to a sensor on the
secondary side. On the primary side, a voltage-divider
is used to reduce the voltage to a workable level. On
the secondary side, a load resistor is selected so that
the current in the transformer windings is safely within
the transformer’s linear operating region.
Because the impedance seen in the primary side of the
transformer is equal to the impedance of the load resis-
tor in the secondary circuit plus impedance of the
transformer secondary winding at the operating fre-
quency, it is easy to calculate the value of the required
voltage-divider resistors in the primary side. For exam-
ple, assume we want a 500:1 divider ratio and assume
the load resistor is 600Ωand that the impedance of the
transformer secondary is 200Ω. The resistor required in
the primary is
(600 + 200) x 500 = 400kΩ
Often, this resistor is constructed from multiple
instances of a smaller value resistor; in this case, one
might use eight 50kΩresistors. Doing so minimizes the
voltage requirements for the resistor chain and reduces
the possibility that a single point of failure will cause a
catastrophic failure.
Current Sensors
Current Shunt
A current shunt is a low-value (approximately 100μΩto
a 100mΩ) resistor that converts a large-value current
into a small voltage. Shunts make good current sensors
because the output is an extremely linear representa-
tion of the measured current, current shunts can have
very low temperature coefficients, and they are inex-
pensive.
The power dissipated by a current shunt is inversely
proportional to its resistance and proportional to the
square of the output voltage. Consequently, there is
great incentive to reduce the resistance (and hence,
the output voltage) of a shunt. Often, full-scale current
in a shunt produces only a few millivolts of output, mak-
ing a front-end amplifier essential. The MAXQ3180
includes a gain-of-32 amplifier in the current channels
that is automatically cycled in and out, depending on
the input voltage of the current channels.
Current shunts operate at line voltage, thus, the AFE
must be isolated from the line. That means that in a
wye-connected meter, the current sensing must be per-
formed in the neutral return circuit (so that all voltages
into the current-sense amplifiers are referenced to neu-
tral). It also means that the use of a shunt is precluded
for delta-connected meters; the MAXQ3180 cannot tol-
erate the line-voltage differential between channels.
Current Transformer
In a current transformer, the primary is usually one turn
of thick wire or buss bar and the secondary is often
1000 turns or more of magnet wire. A ferrite core mag-
netically couples the two. Thus, a large current in the
primary turn creates a small current but large voltage in
the secondary winding.
For example, assume a current transformer with a 1000
turn secondary. A 10A current in the primary winding
induces a 10mA current in the secondary. This current
is made to flow through a so-called “burden” resistor,
usually 10Ωto 20Ω. Assuming a 20Ωburden, our 10A
current thus produces a 200mV signal in the secondary.
Advanced Operation
Modifying the ADC Operation
There are several other registers that directly affect the
AFE function. These registers directly affect the hard-
ware functionality, and should be modified only when it
is explicitly required. For example, if the MAXQ3180 is
operated at some frequency other than the nominal
8MHz system clock, modification of these registers by
supervisory code becomes necessary to maintain a
320μs frame time.
R_ACFG: This register contains bits that disable the
ADC entirely, disable the voltage reference buffer
amplifier, and disable the ADC interrupt. Modifying
this register will likely disable or impair operation of
the MAXQ3180 internal firmware.
R_ADCRATE: Modify this register to change the rate
at which the MAXQ3180 acquires samples. By
default, R_ADCRATE contains 319 decimal, which
means that the ADC acquires a sample every 320
system clocks. With an 8MHz clock, this translates to
40μs. If the system clock is slower, it may be advan-
tageous to reduce this value to keep a 40μs per sam-
ple time constant.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
70 ______________________________________________________________________________________
R_ADCACQ: Modify this register to change the
acquisition time. The acquisition time is the time from
ADC power-on until conversion starts, and is provid-
ed to allow the input amplifiers to settle. By default
this is set to 47 decimal, or 6μs at an 8MHz system
clock. If the system clock rate is changed, then
R_ADCACQ should change so that this value
remains about 6μs.
Fine-Tuning the DSP Controls
Fine-Tuning the Line Frequency Measurement
Line frequency measurement is based on zero-crossing
detection. For that purpose each voltage signal is
passed through a digital lowpass filter, controlled by
the ZC_LPF register. This register specifies the b0coef-
ficient of a first-order LPF using following formula:
The MSB of this register must be zero.
For each phase A, B, and C, the MAXQ3180 counts the
number of scan frames (NS) between zero crossings
within a DSP cycle. Each individual phase A, B, or C
zero-crossing event contributes the raw NS count that
plugs as input to lowpass filter:
Yn= Yn - 1 + (AVG_NS/65,536) x (Xn- Yn - 1)
The filter coefficient is a signed 16-bit value and can be
configured by master. Here Y denotes the global NS
value, X denotes individual NS measurements pro-
duced by zero-crossing events detected on the phase
A, B, or C voltage channel. Note that if all three phase
voltages present, the filter above receives three inputs
each DSP cycle. The global NS value is used to gener-
ate the trigger for DSP processing. Note that the NS
value can be configured by the master, which could be
necessary if all three voltage signals are lost and no
zero-crossings are detected. The line period is then
calculated as a product of NS and the scan frame tFR.
The reciprocal of this value is the line frequency, which
can be obtained as a fixed-point value with 1 LSB =
0.001Hz by reading the LINEFR register.
Fundamental Mode Registers
The MAXQ3180 keeps another set of real and virtual
registers to track power and energy at the fundamental
line frequency. These “fundamental mode” registers
behave identically to the standard power and energy
registers, but are prefiltered to exclude harmonic
power.
The fundamental mode filter is specified in the B0FUND
and A1FUND registers. B0FUND is the feed-forward
coefficient and specifies the bandwidth of the funda-
mental mode filter; A1FUND is the feedback coefficient
and specifies the center frequency of the fundamental
mode filter.
In most cases, you can leave these filters at their
default values. If you wish to change the filter parame-
ters, first choose the desired bandwidth:
b0= πx bw x tFR
In this equation, bw is the desired bandwidth in hertz
and tFR is the frame period, typically 320μs. Set
B0FUND to b0x 216. By default, B0FUND contains dec-
imal 145 (0x91) giving a bandwidth of about 2.2Hz.
To set the center frequency, calculate a1according to
the following formula:
a1= 2 - 2(1 - b0) x cos(2πx fPK x tFR)
In this equation, b0is the previously calculated feed-
forward coefficient, fPK is the desired center frequency
in hertz, and tFR is the ADC frame period. Set A1FUND
to a1x 216. By default, A1FUND contains decimal 950
(0x3B6) giving a center frequency of 50Hz.
The fundamental mode filter is, by default, quite sharp
with 3dB points only 1.1Hz off of the center frequency.
This means that if the frequency drifts even only slight-
ly, the fundamental mode power measurement is likely
to have significant inaccuracy.
The MAXQ3180 provides a mechanism to track the fre-
quency by updating the A1FUND register on each DSP
cycle. This mechanism is automatically enabled by
default.
You may wish to disable the automatic tracking facility
under some circumstances, particularly if you have
defined a broader bandwidth than default and are com-
fortable that the frequency will not drift beyond the
passband. To disable the filter, set the DFUNA bit in the
OPMODE2 register.
You may also elect to disable fundamental mode oper-
ation completely. To do this, set the DFUN bit in the
OPMODE2 register.
Harmonic Measurement
In addition to the ability to measure power and energy
at the fundamental frequency, the MAXQ3180 provides
a mechanism to isolate a particular harmonic on any
voltage or current channel and measure the amplitude
of that harmonic.
To enable harmonic measurement, first select a voltage
or current channel to monitor. This is done in the
AUX_CFG register. The AUX_MUX field is the 3-bit
value that selects one of the three voltage channels or
one of the four current channels to monitor.
bZC LPF
016
2
=_
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 71
The order of the harmonic is set in ORDH field of the
AUX_CFG register.
Also in the AUX_CFG register are two bits that enable
the auxiliary channel and enable harmonic measure-
ment on the auxiliary channel. To enable the auxiliary
channel, set the ENAUX bit. Once set, the MAXQ3180
will perform an RMS calculation on the selected chan-
nel. This is useful only for the IN(neutral current) chan-
nel, since every other voltage and current already have
RMS calculations applied by default. (The DADCNV bit
should be cleared in the SCAN_IN register in order to
enable sampling the INchannel.)
To enable harmonic measurement, set the ENHARM
bit. Now, the selected voltage or current signal is
passed to a filter that is identical to the second-order
fundamental filter, but that has separate parameters
(A1HARM, B0HARM).
Low-Power Measurement Mode (LOWPM)
This mode enables a subset of metering functions while
operating from the lower frequency internal RC oscilla-
tor to conserve power. The actual system clock fre-
quency used is the RC oscillator output frequency
divided by 8, which results in a system clock frequency
of approximately 1MHz.
The parameters provided in the LOWPM are:
Voltage RMS
Current RMS
Ampere-Hour
The ampere-hour value is readable from the X.ESF reg-
isters (X = A/B/C). Entry to LOWPM mode only occurs
at the request of the master. The master must set the
LOWPM_E bit (register address 0xC03) to 1 to place
the MAXQ3180 into LOWPM mode. Entering LOWPM
mode changes the clock frequency, thereby invalidat-
ing a number of configuration registers. As a result, the
master must immediately reload the configuration regis-
ters and filter with new, updated values before metering
measurement operations can continue.
The master instructs the MAXQ3180 to exit LOWPM
mode by reading the LOWPM_X bit (register address
0xC04).
Temperature
The MAXQ3180 contains a temperature sensor that can
be used by host software for any purpose, including
compensating power readings for temperature effects.
Use the virtual register command (RAWTEMP, 0xC01)
to perform a temperature conversion. The MAXQ3180
returns raw ADC reading of voltage produced by the
temperature sensor.
Conversion from the arbitrary units to useful units (such
as degrees Celsius) requires taking one calibration
point and storing a conversion constant in the host
processor. The conversion constant is simply the value
(in absolute degrees) of one LSB.
To calculate the LSB value, take a reading at a known
temperature and divide the known temperature by the
reading. For example, assume you take a reading at
room temperature (23°C), and the reading is 0x7F00.
The degrees per LSB are then:
(23 + 273.15)/0x7F00 = 0.00911K
Now, assume at a later time you read the temperature
and see it is 0x84F0. To find the temperature in Celsius,
multiply by the degrees per LSB and subtract 273.15:
0x84F0 x 0.00911 - 273.15 = 36.8°C
Advanced Calibrations
Calibrating Current Offset
Ideal hardware should produce a current reading lin-
early proportional to the input current. However, due to
noise or other factors, the RMS current read by the
meter might not be precisely linear. The current offset
(X.OFFS_HI, X = A/B/C) can be used to compensate
the current channel nonlinearity.
Since the MAXQ3180 tracks the input current to deter-
mine what linearity compensation factors to use, the
user must choose two points (ilo and ihi) comfortably
above the low current threshold, and get the X.IRMS
current readings (rlo and rhi). Then calculate the Y-inter-
cept of the line drawn between the two points, that is,
the offset. To calculate the value for the offset register,
use the following formula. If LINFRM = 0:
If LINFRM = 1:
In this equation, ihi and rhi are the applied current and
the current reading, respectively, in meter units at the
higher of the two reference currents; ilo and rlo are the
applied current and the current reading, respectively, in
meter units at the lower of the two reference currents.
The gain (X.I_GAIN) may require recalibration after the
offset register updated.
offs ri ir
ii
hi lo hi lo
lo hi
=
()24
offs ri ir
ii
hi lo hi lo
hi lo
=
22 22
24 2 2
2( )
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
72 ______________________________________________________________________________________
Calibrating Linearity
The current channel includes a variable-gain amplifier
that introduces a gain of 32 when the current falls
below the low current threshold (about 1/32 of full-scale
current IFS). Because the gain of the amplifier cannot
be controlled with arbitrary precision, and because
high gain implies increased noise, it may be necessary
to calibrate the MAXQ3180 to maintain linearity at the
lowest inputs.
There are two settings that manage low-current lineari-
ty: an offset setting, OFFS_LO; and a gain setting,
GAIN_LO. Setting the offset is simple. Ensure no cur-
rent is flowing in the current circuit. Read X.IRMS. To
calculate offset use following formula:
If LINFRM = 0:
If LINFRM = 1:
offs = -X.IRMS
Program the offs into the OFFS_LO register.
So, if the user reads 0x0113 from the X.IRMS register and
LINFRM = 1, program 0xFEED into the OFFS_LO register.
Setting the GAIN_LO register means applying a current
below the low-current threshold, reading the value from
the MAXQ3180, and adjusting the gain accordingly. Note
that, unlike offset, the low-end gain is
added
to the overall
gain provided in the I_GAIN register.
Apply a known current with peak value less than the
low-current threshold. Ensure that there is no previous
value in the low-current gain register, A.GAIN_LO, by
setting this register to 0x4000. Read the A.IRMS regis-
ter (0x1CC). Note the value. Convert the known value to
meter units by multiplying the known value (in amperes)
by 224 and dividing by IFS. Divide the results of this cal-
culation by the value read from the MAXQ3180. The
result should be a value between 0 and 2. Convert the
integer by multiplying 214, and ensure MSB is zero. The
result is the gain value to be programmed into
A.GAIN_LO.
Calibrating Power/Energy Gain
Once voltage and current have been calibrated, the
energy and power calculation automatically reflects the
calibrated voltage and current. However the energy
gain factor (X.E_GAIN, X = A/B/C) can be further tuned
to achieve even more accurate power and energy
result if necessary. For example, if the voltage and cur-
rent calibration sources are not as accurate as the
power/energy calibration source, then the additional
gain calibration may be necessary. The following pro-
cedure for power/energy gain calibration is outlined for
phase A.
Apply a precision unity power factor power (applied
value) that is close to the desired normal operating
point.
Read the PWRP.A register. Note the value.
Convert the applied value to meter units by dividing it
by MU_PWR.
Divide the applied value (in meter unit) by the value
read from the MAXQ3180. The result should be a
value between 0 and 2. If the value falls outside of
this range, IFS and/or VFS have probably been mis-
calculated.
Multiply the calculated value by 214, and ensure the
MSB is zero. The result is the gain value to be pro-
grammed into A.E_GAIN.
When the gain value is programmed, wait for 1 to 2
seconds, then reread the power value from PWRP.A.
Check that the measured value is correct by compar-
ing PWRP.A against the applied power in meter unit.
Multipoint Phase Offset Calibration
To perform the calibration at three current levels, note
the raw current value (X.IRMS) at each point. Label the
current values, from highest to lowest, I0, I1, and I2.
Program X.PA0, X.PA1, and X.PA2 with the phase offset
values calculated at I0, I1, and I2, respectively, as
described in the
Calibrating Phase Offset
section.
Finally, program I1THR with the average of I0and I1,
and program I2THR with the geometric average of I1
and I2. Now as the current changes the phase offset is
adjusted accordingly. See Figure 16.
offs XIRMS
=−(. )
2
16
2
0
1
2
I2THR
I1THR
PA2
I2I1I0
PA1
PA0
INPUT CURRENT
PHASE OFFSET
Figure 16. Phase Offset vs. Input Current Calibration
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 73
Advanced Register Configurations
Analog Scan Configuration Registers
Time Slot Assignment—Current Channel X = A/B/C (SCAN_IX)
(A: 0x008, B: 0x00C, C: 0x00A)
These registers configure the time slot normally assigned to current channels A/B/C. We recommend leaving these
registers at their default values. If they must be reassigned, one must ensure that all the current and voltage chan-
nels are reassigned properly so that the MAXQ3180 computes the power/energy parameters as intended by your
setup.
Bit: 7 6 5 4 3 2 1 0
Name: ADCMX DADCNV
Reset A: 0x3 0 0 0 0
Reset B: 0x4 0 0 0 0
Reset C: 0x5 0 0 0 0
BIT NAME FUNCTION
7:4 ADCMX
Analog Conversion Select. This four-bit field determines which of the following analog inputs are sampled
during this time slot.
0000 = V0P - VN
0001 = V1P - VN
0010 = V2P - VN
0011 = I0P - I0N (Phase A Current: 0011)
0100 = I1P - I1N (Phase B Current: 0100)
0101 = I2P - I2N (Phase C Current: 0101)
0110 = INP - VN
1xxx = Temperature
All other values are reserved.
3 DADCNV ADC Disable. When set, disables the ADC for this time slot.
2:0 — Reserved.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
74 ______________________________________________________________________________________
Time Slot Assignment—Voltage Channel X = A/B/C (SCAN_VX)
(A: 0x009, B: 0x00D, C: 0x00B)
These registers configure the time slot normally assigned to voltage channels A/B/C. The user may wish to change the
PGG settings to match the voltage sensor. However, it is recommended that the user not modify the ADCMX settings.
BIT NAME FUNCTION
7:4 ADCMX
Analog Conversion Select. This four-bit field determines which of the following analog inputs are sampled
during this time slot.
0000 = V0P - VN (Phase A Voltage: 0000)
0001 = V1P - VN (Phase B Voltage: 0001)
0010 = V2P - VN (Phase C Voltage: 0010)
0011 = I0P - I0N
0100 = I1P - I1N
0101 = I2P - I2N
0110 = INP - VN
1xxx = Temperature
3 DADCNV ADC Disable. When set, disables the ADC for this time slot.
2:0 PGG
Programmable Gain Amplifier Select. This three-bit field configures the programmable-gain amplifier at
the front-end of the analog input. The field has the following values:
000 = Gain of 1
001 = Gain of 2
010 = Gain of 4
011 = Gain of 8
100 = Gain of 16
101 = Gain of 32
All other values are reserved and can cause unpredictable behavior if selected.
Bit: 7 6 5 4 3 2 1 0
Name: ADCMX DADCNV PGG
Reset A: 0x0 0 0x0
Reset B: 0x1 0 0x0
Reset C: 0x2 0 0x0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 75
Time Slot Assignment—Neutral Current Channel (SCAN_IN) (0x00E)
This register configures the time slot normally assigned to the neutral current channel. The user can change the
DADCNV bit to enable/disable neutral current sampling. It is recommended to leave the other bits of this register at
their default values.
Bit: 7 6 5 4 3 2 1 0
Name: ADCMX DADCNV
Reset: 0x6 1 0 0 0
BIT NAME FUNCTION
7:4 ADCMX
Analog Conversion Select. This four-bit field determines which of the following analog inputs are sampled
during this time slot. All other values are reserved. By default, this register is set to 0110.
0000 = V0P - VN
0001 = V1P - VN
0010 = V2P - VN
0011 = I0P - I0N
0100 = I1P - I1N
0101 = I2P - I2N
0110 = INP - VN
1xxx = Temperature
3 DADCNV ADC Disable. When set, disables the ADC for this time slot.
2:0 — Reserved.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
76 ______________________________________________________________________________________
Time Slot Assignment—Temperature Channel (SCAN_TE) (0x00F)
This register configures the time slot normally assigned to the temperature measurement device. This register is
managed by the firmware and should not be modified by the host.
BIT NAME FUNCTION
7:4 ADCMX
Analog Conversion Select. This four-bit field determines which of the following analog inputs are sampled
during this time slot.
0000 = V0P - VN
0001 = V1P - VN
0010 = V2P - VN
0011 = I0P - I0N
0100 = I1P - I1N
0101 = I2P - I2N
0110 = INP - VN
0111 = Auto-zero ADC
1xxx = Temperature
By default, this register is set to 1000.
3 DADCNV ADC Disable. When set, disables the ADC for this time slot.
2:0 PGG
Programmable Gain Amplifier Select. This three-bit field configures the programmable-gain amplifier at
the front end of the analog input. The field has the following values:
000 = Gain of 1
001 = Gain of 2
010 = Gain of 4
011 = Gain of 8
100 = Gain of 16
101 = Gain of 32
All other values are reserved and can cause unpredictable behavior if selected. This register is managed
by the firmware and should not be modified by the host.
Bit: 7 6 5 4 3 2 1 0
Name: ADCMX DADCNV PGG
Reset: 0x8 1 0x2
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 77
Neutral Current and Harmonics
Auxiliary Channel Configuration (AUX_CFG) (0x010)
The MAXQ3180 can monitor the RMS value of one auxiliary channel in addition to its normal processing. The
Auxiliary Channel Configuration register selects which input the auxiliary channel processes and what processing is
applied to the auxiliary channel.
DSP System Configuration
System Clock Frequency (SYS_KHZ) (0x012)
This register contains the system clock frequency in kHz units. Because the default frequency is 8MHz, this register
defaults to 0x1F40.
Bit: 15 14 13 12 11 10 9 8
Name: — ORDH
Reset: 0 0 0 0 0 0 0 0
Bit: 7 6 5 4 3 2 1 0
Name: ENHARM ENAUX AUX_MUX
Reset: 0 0 0 0 0 0 0 0
BIT NAME FUNCTION
15:13, 5:3 Reserved.
12:8 ORDH
Order of Harmonic (1–21). The output of harmonic voltage is read via virtual register 0x830 and current
at 0x840.
7 ENHARM
Enable Auxiliary Channel Harmonic Filter. When set, the auxiliary channel is processed through the
harmonic filter. The parameters for this filter can be set in the B0HARM and A1HARM registers.
6 ENAUX Enable Auxiliary Channel. When set, enables auxiliary channel processing.
2:0 AUX_MUX
Auxiliary Channel Input Select. This three-bit field selects the input to be processed by the auxiliary
channel.
001 = IN
010 = VA
011 = IA
100 = VB
101 = IB
110 = VC
111 = IC
Bit: 15 14 13 12 11 10 9 8
Name: System Clock Frequency High Byte
Reset: 0x1F
Bit: 7 6 5 4 3 2 1 0
Name: System Clock Frequency Low Byte
Reset: 0x40
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
78 ______________________________________________________________________________________
Cycle Count (CYCNT) (0x01C)
This register contains the number of line cycles that will be accumulated in a single DSP cycle. When CYCNT line
cycles have been accumulated, the DSP performs power, power factor, and energy calculations. By default, the
cycle count is 0x10 (16 decimal).
Number of Scan Frames per DSP Cycle (NS) (0x040)
The NS register defines the fundamental timing for the electricity meter. It defines a DSP cycle in terms the period of
the ADC scan frame. Generally, this register is calculated and updated automatically by the MAXQ3180 firmware
based on the zero-crossing detection, and whether noise rejection (REJ_NS) and averaging (AVG_NS) are enabled.
Host code can write to this register in order to set the desired DSP cycle duration. The duration of one scan frame
(tFR) is represented as 0x00010000.
Bit: 15 14 13 12 11 10 9 8
Name: Cycle Count High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Cycle Count Low Byte
Reset: 0x10
Bit: 31 30 29 28 27 26 25 24
Name: Integer Portion, High Byte
Reset: 0x03
Bit: 23 22 21 20 19 18 17 16
Name: Integer Portion, Low Byte
Reset: 0xE8
Bit: 15 14 13 12 11 10 9 8
Name: Fractional Portion, High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Fractional Portion, Low Byte
Reset: 0x00
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 79
Filter Coefficients
Line Cycle Noise Rejection Filter (REJ_NS) (0x02C)
This register establishes the sensitivity of the NS rejection filter setting. NS is a measure of the line frequency. If a line
cycle occurs that is shorter or longer than the line cycle represented in the NS register, this filter determines whether
the cycle is used to update the NS value. For more information, see the NS register description. If this register is
zero, noise rejection is disabled for the line cycle counter.
Line Cycle Averaging Filter (AVG_NS) (0x02E)
This register determines whether the NS value is averaged over previous values or whether the most recently measured
value is used directly. If the value of this register is nonzero, the NS value is averaged using the following formula:
If the value of this register is zero, NS is not averaged. The MSB of this register must be zero.
yy AVGNS
xy
nn nn
=+
11
16
2
_
Bit: 15 14 13 12 11 10 9 8
Name: Line Cycle Noise Rejection Filter High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Line Cycle Noise Rejection Filter Low Byte
Reset: 0xC8
Bit: 15 14 13 12 11 10 9 8
Name: Line Cycle Averaging Filter High Byte
Reset: 0x40
Bit: 7 6 5 4 3 2 1 0
Name: Line Cycle Averaging Filter Low Byte
Reset: 0x00
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
80 ______________________________________________________________________________________
Meter Measurement Averaging Filter (AVG_C) (0x030)
This register determines whether the all other measured values in the electricity meter are averaged over time. If the
value of this register is nonzero, all measured meter values are averaged using the following formula:
If the value of this register is zero, no averaging is performed. The MSB of this register must be zero.
Meter Measurement Highpass Filter (HPF_C) (0x032)
This register specifies the b0coefficient of a first-order Butterworth filter using the following formula:
The MSB of this register must be zero.
bHPF C
016
2
=_
yy AVGC
xy
nn nn
=+
11
16
2
_
Bit: 15 14 13 12 11 10 9 8
Name: Meter Measurement Averaging Filter High Byte
Reset: 0x40
Bit: 7 6 5 4 3 2 1 0
Name: Meter Measurement Averaging Filter Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Meter Measurement Highpass Filter High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Meter Measurement Highpass Filter Low Byte
Reset: 0xC8
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 81
Fundamental Filter Feed-Forward Coefficient (B0FUND) (0x034)
This register specifies the b0(feed-forward) coefficient for the fundamental-mode filter using the following formula:
The MSB of this register must be zero.
Fundamental Filter Feedback Coefficient (A1FUND) (0x036)
This register specifies the a1(feedback) coefficient for the fundamental-mode filter using the following formula:
aA FUND
116
1
2
=
bB FUND
016
0
2
=
Bit: 15 14 13 12 11 10 9 8
Name: Fundamental Filter Feed-Forward Coefficient High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Fundamental Filter Feed-Forward Coefficient Low Byte
Reset: 0x91
Bit: 31 30 29 28 27 26 25 24
Name: Fundamental Filter Feedback Coefficient Byte 3
Reset: 0x00
Bit: 23 22 21 20 19 18 17 16
Name: Fundamental Filter Feedback Coefficient Byte 2
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Fundamental Filter Feedback Coefficient Byte 1
Reset: 0x03
Bit: 7 6 5 4 3 2 1 0
Name: Fundamental Filter Feedback Coefficient Byte 0
Reset: 0xB6
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
82 ______________________________________________________________________________________
Harmonic Filter Feed-Forward Coefficient (B0HARM) (0x03A)
This register specifies the b0(feed-forward) coefficient for the harmonic-mode filter using the following formula:
The MSB of this register must be zero.
Harmonic Filter Feedback Coefficient (A1HARM) (0x03C)
This register specifies the a1(feedback) coefficient for the harmonic mode filter using the following formula:
Zero-Cross Lowpass Filter (ZC_LPF) (0x05A)
This register specifies the lowpass filter applied for zero-cross detection. The MSB of this register must be zero.
aA HARM
116
1
2
=
bB HARM
016
0
2
=
Bit: 15 14 13 12 11 10 9 8
Name: Harmonic Filter Feed-Forward Coefficient High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Harmonic Filter Feed-Forward Coefficient Low Byte
Reset: 0x91
Bit: 31 30 29 28 27 26 25 24
Name: Harmonic Filter Feedback Coefficient Byte 3
Reset: 0x00
Bit: 23 22 21 20 19 18 17 16
Name: Harmonic Filter Feedback Coefficient Byte 2
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Harmonic Filter Feedback Coefficient Byte 1
Reset: 0x18
Bit: 7 6 5 4 3 2 1 0
Name: Harmonic Filter Feedback Coefficient Byte 0
Reset: 0x31
Bit: 15 14 13 12 11 10 9 8
Name: Zero-Cross Lowpass Filter High Byte
Reset: 0x0B
Bit: 7 6 5 4 3 2 1 0
Name: Zero-Cross Lowpass Filter Low Byte
Reset: 0x00
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 83
Hardware Mirror Registers
ADC Configuration (R_ACFG) (0x04C)
This register is a mirror of a CPU register in the MAXQ3180. This register should not be modified by supervisory
code.
ADC Conversion Rate (R_ADCRATE) (0x04E)
This register specifies the number of system clock cycles between consecutive ADC conversions. It defaults to
0x13F (319 decimal), which specifies 320 CPU clock cycles between conversions. This register is a mirror of a CPU
register in the MAXQ3180.
Bit: 7 6 5 4 3 2 1 0
Name: ADCASD ADCRY ADCCD ADCBY ADCIE ARBE ADCE
Reset: 0 0 0x0 0 1 1 1
BIT NAME FUNCTION
7 ADCASD
Disable ADC Automatic Shutdown. Normally, the ADC analog section is powered off following a
conversion to conserve power. If this bit is set, the ADC leaves the analog section powered on
following a conversion.
6 ADCRY
ADC Data Ready. When a conversion is complete, this bit is set to indicate that data is available. This
bit generates an interrupt if ADCIE is set.
5:4 ADCCD
ADC Clock Divider. Sets the division ratio between the CPU master and ADC clock.
00 = divide by 1
01 = divide by 2
10 = divide by 4
11 = reserved
3 ADCBY
ADC Busy. When set, a single ADC conversion cycle is in progress. The bit is cleared on the
conclusion of the conversion cycle.
2 ADCIE ADC Interrupt Enable. If set, the ADC interrupts the CPU at the completion of a conversion cycle.
1 ARBE Reference Buffer Enable. If set, the reference buffer is enabled to drive the REFO pin.
0 ADCE ADC Enable. If set, the ADC hardware is activated.
Bit: 15 14 13 12 11 10 9 8
Name: ADC Conversion Rate High Byte
Reset: — — — — — — 1
Bit: 7 6 5 4 3 2 1 0
Name: ADC Conversion Rate Low Byte
Reset: 0x3F
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
84 ______________________________________________________________________________________
ADC Settling Time (R_ADCACQ) (0x050)
This register is a mirror of a CPU register in the MAXQ3180. This register should not be modified by supervisory
code. This register specifies the time, in CPU clocks, that the ADC must wait after switching analog mux inputs
before beginning its conversion. This register defaults to 0x2F (47 decimal), which specifies a 48 CPU clock-cycle
delay from analog mux switching to the start of conversion.
SPI Configuration (R_SPICF) (0x052)
This register is a mirror of a CPU register in the MAXQ3180. This register configures the SPI port of the MAXQ3180.
Bit: 15 14 13 12 11 10 9 8
Name: ADC Settling Time High Byte
Reset: — — — — — —
Bit: 7 6 5 4 3 2 1 0
Name: ADC Settling Time Low Byte
Reset: 0x2F
Bit: 7 6 5 4 3 2 1 0
Name: ESPII SAS CHR CKPHA CKPOL
Reset: 1 0 0 0 0 0 0 0
BIT NAME FUNCTION
7 ESPII Enable SPI Interrupt. If set, arrival of a character on the SPI bus causes a CPU interrupt.
6 SAS
SPI Slave Select Polarity. If clear, SSEL is assumed to be active low; if set, SSEL is assumed to be
active high.
5:3 — Reserved.
2 CHR
SPI Character Length. If clear, characters on the SPI bus are assumed to be 8 bits; if set, characters on
the SPI bus are assumed to be 16 bits.
1 CKPHA
SPI Clock Phase. If clear, data is sampled on the leading edge of the clock (low-to-high if the clock is
active high, and high-to-low if the clock is active low). If set, data is sampled on the trailing edge of the
clock (high-to-low if the clock is active high, and low-to-high if the clock is active low).
0 CKPOL
SPI Clock Polarity. If clear, the clock is assumed to be active high; if set, the clock is assumed to be
active low.
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 85
Timeouts
Zero-Crossing Timeout (NZX_TIMO) (0x054)
This register specifies the time in ADC sample periods (default 40μs) that must elapse following a zero-crossing
event before the MAXQ3180 declares a “no-zero crossing” fault. When this fault is declared, the NOZXF bit in the
X.FLAGS register is set.
Communications Timeout (COM_TIMO) (0x056)
This register specifies the duration of SPI timeout in ADC frames (default 320μs).
Energy Accumulation Timeout (ACC_TIMO) (0x058)
This register specifies the time in DSP cycles that the MAXQ3180 waits before accumulating energy. If this register is
nonzero, it is decremented on each DSP cycle. If the result of the decrement is nonzero, the results of the DSP cycle
are discarded and are not accumulated to the energy registers. This register is useful for delaying the initiation of
energy accumulation on startup or after some hardware function has been modified.
Bit: 15 14 13 12 11 10 9 8
Name: Zero-Crossing Timeout High Byte
Reset: 0x23
Bit: 7 6 5 4 3 2 1 0
Name: Zero-Crossing Timeout Low Byte
Reset: 0x28
Bit: 15 14 13 12 11 10 9 8
Name: Communications Timeout High Byte
Reset: 0x03
Bit: 7 6 5 4 3 2 1 0
Name: Communications Timeout Low Byte
Reset: 0xE8
Bit: 15 14 13 12 11 10 9 8
Name: Energy Accumulation Timeout High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Energy Accumulation Timeout Low Byte
Reset: 0x05
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
86 ______________________________________________________________________________________
Phase-Angle Compensation
Phase Offset Current Threshold 1 (I1THR) (0x05C)
This register specifies the fraction of full-scale current that causes the MAXQ3180 to switch from PA0 to PA1 to pro-
vide phase-angle compensation. For more information, see the PA0, PA1, and PA2 register descriptions. The full-
scale current is represented by 0x10000.
Phase Offset Current Threshold 2 (I2THR) (0x05E)
This register specifies the fraction of full-scale current that causes the MAXQ3180 to switch from PA1 to PA2 to pro-
vide phase-angle compensation. For more information, see the PA0, PA1, and PA2 register descriptions. The full-
scale current is represented by 0x10000.
Miscellaneous Gain
Neutral Current Gain (N.I_GAIN) (0x12E)
This register contains gain compensation coefficient for the neutral current channel measurement. The raw values
are taken from the selected measurement quantity and scaled by N.I_GAIN/214.
Bit: 15 14 13 12 11 10 9 8
Name: Phase Accumulator Current Threshold 1 High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Phase Accumulator Current Threshold 1 Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Phase Accumulator Current Threshold 2 High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Phase Accumulator Current Threshold 2 Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Compensation Coefficient High Byte
Reset: 0x40
Bit: 7 6 5 4 3 2 1 0
Name: Compensation Coefficient Low Byte
Reset: 0x00
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 87
Gain, Fundamental Energy, Phase X = A/B/C (X.EF_GAIN) (A: 0x136, B: 0x222, C: 0x30E)
This register contains gain coefficient for phase X fundamental energy. The raw values are taken from the selected
measurement quantity and scaled by the following factor:
Linearity Compensation
Linearity Offset, High Range, Phase X = A/B/C (X.OFFS_HI) (A: 0x138, B: 0x224, C: 0x310)
This signed register contains the linearity offset for phase X current channel when the programmable gain amplifier
is set to unity gain (that is, the measured current is above the low current threshold). The signed value represented
by this register is added to the current value according to following formula:
if LINFRM = 0:
if LINFRM = 1: X.IRMS + X.OFFS_HI x 24
Linearity Gain Coefficient, Low Range, Phase X = A/B/C (X.GAIN_LO)
(A: 0x13A, B: 0x226, C: 0x312)
This register contains the linearity coefficient for phase X current channel when the programmable gain amplifier is
set to gain of 32 (that is, the measured current is below the low current threshold). The effective gain is given by the
equation:
XGAIN LO._
214
XIRMS XOFFS HI.._
224
2
XEF GAIN._
214
Bit: 15 14 13 12 11 10 9 8
Name: Gain Coefficient High Byte
Reset: 0x40
Bit: 7 6 5 4 3 2 1 0
Name: Gain Coefficient Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Linearity Offset High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Linearity Offset Low Byte
Reset: 0x00
Bit: 15 14 13 12 11 10 9 8
Name: Linearity Coefficient High Byte
Reset: 0x40
Bit: 7 6 5 4 3 2 1 0
Name: Linearity Coefficient Low Byte
Reset: 0x00
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
88 ______________________________________________________________________________________
Linearity Offset, Low Range, Phase X = A/B/C (X.OFFS_LO) (A: 0x13C, B: 0x228, C: 0x314)
This signed register contains the linearity offset for phase X current channel when the programmable gain amplifier
is set to gain of 32 (that is, the measured current is below the low current threshold). The signed value represented
by this register is added to the current value. The total linearity compensation is applied as follows:
if LINFRM = 0: X.GAIN_LO/214 x
if LINFRM = 1: X.GAIN_LO/214 x (X.IRMS + X.OFFS_LO)
Measurements—RAM Registers
On-Demand RMS Result (N.IRMS) (0x11C)
This register contains the result of the RMS calculation on the AUX channel. Usually, this is the neutral current chan-
nel, but can be defined to be the RMS average of any harmonic of the quantities defined in the AUX_MUX field of the
AUX_CFG register.
XIRMS XOFFS LO.._
216
2
Bit: 15 14 13 12 11 10 9 8
Name: Linearity Offset High Byte
Reset: 0x00
Bit: 7 6 5 4 3 2 1 0
Name: Linearity Offset Low Byte
Reset: 0x00
Bit: 31 30 29 28 27 26 25 24
Name: RMS Result, Byte 3
Reset:
Bit: 23 22 21 20 19 18 17 16
Name: RMS Result, Byte 2
Reset:
Bit: 15 14 13 12 11 10 9 8
Name: RMS Result, Byte 1
Reset:
Bit: 7 6 5 4 3 2 1 0
Name: RMS Result, Byte 0
Reset:
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 89
Fundamental Energy
Fundamental Energy Overflow Flags, Phase X = A/B/C (X.EFOVER)
(A: 0x147, B: 0x233, C: 0x31F)
These bits indicate an overflow condition has occurred on a fundamental frequency energy accumulator. An over-
flow condition is not an error condition. Rather, it simply indicates that the value in the energy accumulator could be
smaller than the previous reading due to the overflow in the counter. To obtain the actual energy usage since the
previous reading, 0x100000000 must be added to the difference. These bits, once set, can be cleared only by the
host.
Energy, Fundamental, Real Positive, Phase X = A/B/C (X.EAFPOS)
(A: 0x1FC, B: 0x2E8, C: 0x3D4)
On every DSP cycle, the contents of the X.ACTF register are tested, and if positive, are added to this register. When
this register overflows, the APFOV bit in the X.EFOVER register is set.
BIT NAME FUNCTION
7:5 — Reserved.
4 SFOV When set, indicates an overflow condition on the apparent fundamental-mode energy accumulator.
3 RNFOV When set, indicates an overflow condition on the reactive negative fundamental-mode energy accumulator.
2 RPFOV When set, indicates an overflow condition on the reactive positive fundamental-mode energy accumulator.
1 ANFOV When set, indicates an overflow condition on the real negative fundamental-mode energy accumulator.
0 APFOV When set, indicates an overflow condition on the real positive fundamental-mode energy accumulator.
Bit: 7 6 5 4 3 2 1 0
Name: SFOV RNFOV RPFOV ANFOV APFOV
Reset: 0 0 0 0 0 0 0 0
Bit: 31 30 29 28 27 26 25 24
Name: Real Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Real Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Real Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Real Energy Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
90 ______________________________________________________________________________________
Energy, Fundamental, Real Negative, Phase X = A/B/C (X.EAFNEG)
(A: 0x200, B: 0x2EC, C: 0x3D8)
On every DSP cycle, the contents of the X.ACTF register are tested, and, if negative, absolute values are added to
this register. When this register overflows, the ANFOV bit in the X.EFOVER register is set.
Energy, Fundamental, Reactive Positive, Phase X = A/B/C (X.ERFPOS)
(A: 0x204, B: 0x2F0, C: 0x3DC)
On every DSP cycle, the contents of the X.REAF register are tested, and, if positive, are added to this register. When
this register overflows, the RPFOV bit in the X.EFOVER register is set.
Bit: 31 30 29 28 27 26 25 24
Name: Real Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Real Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Real Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Real Energy Byte 0
Bit: 31 30 29 28 27 26 25 24
Name: Reactive Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Reactive Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Reactive Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Reactive Energy Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 91
Energy, Fundamental, Reactive Negative, Phase X = A/B/C (X.ERFNEG)
(A: 0x208, B: 0x2F4, C: 0x3E0)
On every DSP cycle, the contents of the X.REAF register are tested, and, if negative, absolute values are added to
this register. When this register overflows, the RNFOV bit in the X.EFOVER register is set.
Energy Fundamental, Apparent, Phase X = A/B/C (X.ESF)
(A: 0x20C, B: 0x2F8, C: 0x3E4)
On every DSP cycle, the contents of the X.ESF register are added to this register. When this register overflows, the
SFOV bit in the X.EFOVER register is set. When the MAXQ3180 is operating in low-power mode, energy is not accu-
mulated. However, during low-power mode, current values are accumulated to this register, making this register
accumulate ampere-hours.
Bit: 31 30 29 28 27 26 25 24
Name: Reactive Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Reactive Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Reactive Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Reactive Energy Byte 0
Bit: 31 30 29 28 27 26 25 24
Name: Apparent Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Apparent Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Apparent Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Apparent Energy Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
92 ______________________________________________________________________________________
Energy Accumulated in the Last DSP Cycle
Real Energy, Phase X = A/B/C (X.ACT) (A: 0x1D0, B: 0x2BC, C: 0x3A8)
This signed register provides the raw real energy accumulated over the most recent DSP cycle. For each ADC sam-
ple period, the real instantaneous power calculated from the instantaneous voltage and current is accumulated. At
the end of each DSP cycle, the result of the accumulation over the DSP cycle is copied to this register and is accu-
mulated in X.EAPOS or X.EANEG, depending on the sign of the accumulated energy.
LSB of the energy registers is VFS x IFS x tFR/216.
Reactive Energy, Phase X = A/B/C (X.REA) (A: 0x1D4, B: 0x2C0, C: 0x3AC)
This signed register provides the raw reactive energy accumulated over the most recent DSP cycle. For each ADC
sample period, the reactive instantaneous power calculated from the instantaneous voltage and current is accumu-
lated. At the end of each DSP cycle, the result of the accumulation over the DSP cycle is copied to this register and
is accumulated in X.ERPOS or X.ERNEG, depending on the sign of the accumulated energy.
Bit: 31 30 29 28 27 26 25 24
Name: Real Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Real Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Real Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Real Energy Byte 0
Bit: 31 30 29 28 27 26 25 24
Name: Reactive Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Reactive Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Reactive Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Reactive Energy Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 93
Apparent Energy, Phase X = A/B/C (X.APP) (A: 0x1D8, B: 0x2C4, C: 0x3B0)
This signed register provides the raw apparent energy accumulated over the most recent DSP cycle.
Fundamental Energy Accumulated in the Last DSP Cycle
Fundamental Real Energy, Phase X = A/B/C (X.ACTF) (A: 0x1DC, B: 0x2C8, C: 0x3B4)
This signed register accumulates energy in the same fashion as the X.ACT register, but only at the fundamental line
frequency.
Bit: 31 30 29 28 27 26 25 24
Name: Apparent Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Apparent Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Apparent Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Apparent Energy Byte 0
Bit: 31 30 29 28 27 26 25 24
Name: Real Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Real Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Real Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Real Energy Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
94 ______________________________________________________________________________________
Fundamental Reactive Energy, Phase X = A/B/C (X.REAF) (A: 0x1E0, B: 0x2CC, C: 0x3B8)
This signed register accumulates energy in the same fashion as the X.REA register, but only at the fundamental line
frequency.
Fundamental Apparent Energy, Phase X = A/B/C (X.APPF) (A: 0x1E4, B: 0x2D0, C: 0x3BC)
This register accumulates energy in the same fashion as the X.APP register, but only at the fundamental line frequency.
Bit: 31 30 29 28 27 26 25 24
Name: Reactive Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Reactive Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Reactive Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Reactive Energy Byte 0
Bit: 31 30 29 28 27 26 25 24
Name: Apparent Energy Byte 3
Bit: 23 22 21 20 19 18 17 16
Name: Apparent Energy Byte 2
Bit: 15 14 13 12 11 10 9 8
Name: Apparent Energy Byte 1
Bit: 7 6 5 4 3 2 1 0
Name: Apparent Energy Byte 0
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 95
Checksum (CHKSUM) (0x060)
This register contains the calculated 16-bit arithmetic checksum over critical configuration and calibration registers.
It is updated on every DSP cycle. In use, the administrative processor records the value in the CHKSUM register and
then checks it periodically to verify that no configuration or calibration registers have changed. The MAXQ3180 sets
the CHSCH bit when this register’s value changes.
The registers included in the checksum calculation include the following:
Bit: 15 14 13 12 11 10 9 8
Name: Checksum High Byte
Reset:
Bit: 7 6 5 4 3 2 1 0
Name: Checksum Low Byte
Reset:
SYS_KHZ THR2 R_ADCRATE A.I_GAIN B.I_GAIN C.I_GAIN
VOLT_CC REJ_NS R_ADCACQ A.V_GAIN B.V_GAIN C.V_GAIN
AMP_CC AVG_NS R_SPICF A.E_GAIN B.E_GAIN C.E_GAIN
PWR_CC AVG_C NZX_TIMO A.EF_GAIN B.EF_GAIN C.EF_GAIN
ENR_CC HPF_C COM_TIMO A.OFFS_HI B.OFFS_HI C.OFFS_HI
CYCNT B0FUND ACC_TIMO A.GAIN_LO B.GAIN_LO C.GAIN_LO
PLSCFG1 OCLVL I1THR A.OFFS_LO B.OFFS_LO C.OFFS_LO
PLSCFG2 OVLVL I2THR A.PA0 B.PA0 C.PA0
PLS1_WD UVLVL ZC_LPF A.PA1 B.PA1 C.PA1
THR1 NOLOAD A.PA2 B.PA2 C.PA2
PLS2_WD R_ACFG
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
96 ______________________________________________________________________________________
Measurements—Virtual Registers
Fundamental Real Power, Phase A/B/C/T (PWRPF.X)
(A: 0x881, B: 0x882, C: 0x884, T: 0x887)
This signed register contains the real instantaneous power delivered into phase A/B/C or total at the fundamental line
frequency only. Power is calculated from the instantaneous energy measurement according to the following equation:
Fundamental Reactive Power, Phase A/B/C/T (PWRQF.X)
(A: 0x891, B: 0x892, C: 0x894, T: 0x897)
This signed register contains the reactive instantaneous power delivered into phase A/B/C or total at the fundamental
line frequency only. Power is calculated from the instantaneous energy measurement according to the following
equation:
PWRQF X XREAF PWR CC
NS
.._
=××216
PWRPF X X ACTF PWR CC
NS
.._
=××216
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 97
Fundamental Apparent Power, Phase A/B/C/T (PWRSF.X)
(A: 0x8A1, B: 0x8A2, C: 0x8A4, T: 0x8A7)
This register contains the instantaneous apparent power delivered into phase A/B/C or total at the fundamental line
frequency only. Power is calculated from the instantaneous energy measurement according to the following equation:
Fundamental Real Energy, Phase A/B/C/T (ENRPF.X)
(A: 0x8E1, B: 0x8E2, C: 0x8E4, T: 0x8E7)
This signed register contains the real accumulated energy delivered into phase A/B/C or total. The register is calcu-
lated according to the following formula:
ENRPF.X = ENR_CC x (X.EAFPOS - X.EAFNEG)
Fundamental Reactive Energy, Phase A/B/C/T (ENRQF.X)
(A: 0x8F1, B: 0x8F2, C: 0x8F4, T: 0x8F7)
This signed register contains the reactive accumulated energy delivered into phase A/B/C or total. The register is
calculated according to the following formula:
ENRQF.X = ENR_CC x (X.ERFPOS - X.ERFNEG)
Fundamental Apparent Energy, Phase A/B/C/T (ENRSF.X)
(A: 0x8B1, B: 0x8B2, C: 0x8B4, T: 0x8B7)
This register contains the apparent accumulated energy delivered into phase A/B/C or total. The register is the prod-
uct of the ENR_CC and X.ESF registers.
PWRSF X X APPF PWR CC
NS
.._
=××216
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
Byte 7 (MSByte unused) Byte 6 (unused)
Byte 5 Byte 4
Byte 3 Byte 2
Byte 1 Byte 0 (LSByte)
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
98 ______________________________________________________________________________________
Phasors
Phase B Phasor (VBPH: 0x852)
This register reports phase angle of voltage phase B
with respect to voltage phase A. The value is
expressed in units of 0.01 degree; thus, the nominal
value is 12000 decimal (0x2EE0). This value is calculat-
ed based on zero-crossing detection. It may exhibit
noticable error in the presence of harmonics on voltage
channels. This register is 2 bytes wide.
Phase C Phasor (VCPH: 0x854)
This register reports phase angle of voltage phase C
with respect to voltage phase A. The value is
expressed in units of 0.01 degree; thus, the nominal
value is 24000 decimal (0x5DC0). This value is calcu-
lated based on zero-crossing detection. It may exhibit
noticable error in the presence of harmonics on voltage
channels. This register is 2 bytes wide.
Harmonics
RMS Voltage, Harmonic (V.HARM) (0x830)
This register reports the RMS voltage. The units are
defined by the VOLT_CC setting. Use AUX_CFG to
configure the phase (A/B/C) and harmonic order
desired.
RMS Current, Harmonic/Neutral (I.N, I.HARM) (0x840)
This register reports the harmonic RMS current of
selected phase (A/B/C) and harmonic order, harmonic,
or the RMS current of the neutral current channel. The
units are defined by the AMP_CC setting. Use
AUX_CFG to configure the phase (A/B/C) and harmonic
order desired.
Ratio of Harmonic/Fundamental (HARM_NF) (0x850)
This register reports the ratio of the selected harmonic
RMS over the fundamental RMS of the same signal
(except IN). The master must configure the AUX_CFG
register to enable the AUX channel, enable harmonics,
and select AUX_MUX before reading this register. This
register is 4 bytes wide with the resolution of 1/216.
Special Commands
Table 7 shows the read-only virtual registers that acti-
vate special commands when read by the master.
Some commands return dummy values.
Applications Information
Grounds and Bypassing
Careful PCB layout significantly minimizes noise on the
analog inputs, resulting in less noise on the digital I/O
that could cause improper operation. The use of multi-
layer boards is essential to allow the use of dedicated
power planes. The area under any digital components
should be a continuous ground plane if possible. Keep
any bypass capacitor leads short for best noise rejec-
tion and place the capacitors as close to the leads of
the devices as possible.
The MAXQ3180 must have separate ground areas for
the analog (AGND) and digital (DGND) portions, con-
nected together at a single point.
NAME ADDRESS DESCRIPTION
DATA
LENGTH
(BYTES)
UPD_SFR 0x900
Reading this register copies the mirror registers (R_ADCF, R_ADCRATE,
R_ADCACQ, R_SPICF) into hardware SFR registers. The read returns dummy data. 1
UPD_MIR 0xA00
Reading this register copies hardware SFR registers into mirror registers (R_ADCF,
R_ADCRATE, R_ADCACQ, R_SPICF). The read returns dummy data. 1
DSPVER 0xC00 Reading this register returns the DSP firmware version number. 2
RAWTEMP 0xC01
Reading this register initiates the sampling and averaging of two internal
temperature readings. The result in internal temperature units is read from this
register LSB first. Use the following equation to convert a raw temperature reading to
Celsius: T[c] = T[raw] x TempFactor - 273.15
where TempFactor is a value to be determined by calibration. Note that the final
value may be slightly higher than ambient due to internal die heating.
2
ENTER STOP 0xC02 Reading this register places the device into Stop Mode. 1
ENTER LOWPM 0xC03 Reading this register places the device into LOWPM Mode. 1
EXIT LOWPM 0xC04 Reading this register exits LOWPM Mode. 1
Table 7. Virtual Registers That Activate Special Commands
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
______________________________________________________________________________________ 99
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages.
CMOS design guidelines for any semiconductor require
that no pin be taken above DVDD or below DGND.
Violation of this guideline can result in a hard failure
(damage to the silicon inside the device) or a soft fail-
ure (unintentional modification of memory contents).
Voltage spikes above or below the device’s absolute
maximum ratings can potentially cause a devastating
IC latchup.
Microcontrollers commonly experience negative volt-
age spikes through either their power pins or general-
purpose I/O pins. Negative voltage spikes on power
pins are especially problematic as they directly couple
to the internal power buses. Devices such as keypads
can conduct electrostatic discharges directly into the
microcontroller and seriously damage the device.
System designers must protect components against
these transients that can corrupt system memory.
Specific Design Considerations for
MAXQ3180-Based Systems
To reduce the possibility of coupling noise into the
microcontroller, the system should be designed with a
crystal or oscillator in a metal case that is grounded to
the digital plane. Doing so reduces the susceptibility of
the design to fast transient noise.
Because the MAXQ3180 is designed for use in systems
where high voltages are present, care must be taken to
route all signal paths, both analog and digital, as far
away as possible from the high-voltage components.
It is possible to construct more elaborate metering
designs using multiple MAXQ3180 devices. This can be
accomplished by using a single SPI bus to connect all
the MAXQ3180 devices together but using separate
slave select lines to individually select each MAXQ3180.
Additional Documentation
Designers must ensure they have the latest MAXQ3180
errata documents. Errata sheets contain deviations
from published specifications. A MAXQ3180 errata
sheet for any specific device revision is available at
www.maxim-ic.com/errata.
Technical Support
For technical support, go to https://support.maxim-
ic.com/micro.
PACKAGE TYPE PACKAGE CODE DOCUMENT NO.
28 TSSOP U28+3 21-0066
TOP VIEW
MAXQ3180
TSSOP
254 AVDDI0N
263 V0PI0P
272 V1P
INP
281 V2PVN
227 DVDD
I2P
236 VCOMMI1N
218 RESETI2N
209 CFQAGND
1910 CFPXTAL2
1811 DGNDXTAL1
1712 DVDDIRQ
1613 MISOSSEL
245 VREF
I1P
1514 MOSISCLK
Pin Configuration
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
100 _____________________________________________________________________________________
MAXQ3180
V0P
SSEL
SCLK
MOSI
MISO
R1
R2
V1P
R1
R2
V2P
VN
VCOMM
R1
R2
I0P
I0N
R3
R3
I1P
I1N
I2P
I2N
VOLTAGE SENSE
VA
VB
VC
N
CURRENT TRANSFORMER
LC
LB
LA
R3
R3
R3
R3
MASTER
Typical Application Circuit
MAXQ3180
Low-Power, Multifunction, Polyphase AFE
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101
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Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 2/08 Initial release.
1 1/09 Updated data sheet to be consistent with additional device features. All
Removed reference to the device supporting IEC standards in the Features section;
changed the precision internal voltage reference spec from 1.23V to 2.048V. 1
In the Electrical Characteristics table, changed stop-mode current TYP and MAX from
A and 0μA to 0.2μA and 12μA, respectively; changed the input voltage range MAX
from 2V to VREF V; added VREF to output voltage SYMBOL; changed the tSCH and tSCL
MIN to 4 x tSYS and added Note 3 to CONDITIONS; changed the output voltage spec
for the internal voltage reference from 1.23V (typ) to 2.048V (typ); changed the
maximum SPI clock rate spec for the SPI slave-mode interface timing from 2MHz
(max) to fSYS/4MHz (max), and changed the tSE, tSD, tSIS, tSIH, and tSOV specs;
updated the SPI Slave Mode Timing diagram.
10, 11, 12
Updated the CFP and CFQ descriptions in the Pin Description table. 14
Removed statement about the IRQ line dropping low when reset causes the device
to enter Initialization Mode in the Watchdog Reset section. 17
Added new paragraph to the Host Software Design section about reading the virtual
registers. 24
Removed the Code Examples section. 26, 27, 28
Updated the bit functions for PORF and WDTR in the Global Status Register (STATUS)
(0x000) section. 28
Added bit 14 functionality (DSPRDY) to the IRQ_FLAG register. 33
Added bit 14 functionality (EDSPRDY) to the IRQ_MASK register and updated the
EDSPOR function description. 34
Corrected the reset valued for the OCLVL, OVLVL, and SYS_KHZ registers. 40, 41, 77
Corrected the reference of V/A to A/V in the Units Conversion Examples section
current transducer ratio (ITR) equation. 65
Updated the bit description for ADCMX (SCAN_IX.7:4, SCAN_VX.7:4, SCAN_IN.7:4)
and PGG. 73, 74
Updated the descriptions of the SCAN_IN and SCAN_TE registers. 75, 76
Corrected the reset value to 1 for bit 8 in the R_ADCRATE register. 83
2 8/09
Updated the phase B phasor and phase C phasor nominal values. 98
Changed the voltage range on VxP, IxN relative to AGND to -0.3V to +4.0V in the
Absolute Maximum Ratings section. 10
3 12/09
Added a statement that the CRC be enabled for read and write in the Host Software
Design section. 24