LTC2991
1
2991ff
For more information www.linear.com/LTC2991
TYPICAL APPLICATION
FEATURES DESCRIPTION
Octal I2C Voltage, Current,
and Temperature Monitor
The LT C
®
2991 is used to monitor system temperatures,
voltages and currents. Through the I2C serial interface, the
eight monitors can individually measure supply voltages
and can be paired for differential measurements of cur-
rent sense resistors or temperature sensing transistors.
Additional measurements include internal temperature
and internal VCC. The internal 10ppm reference minimizes
the number of supporting components and area required.
Selectable address and configurable functionality give the
LTC2991 flexibility to be incorporated in various systems
needing temperature, voltage or current data. The LTC2991
fits well in systems needing submillivolt voltage resolution,
1% current measurement and 1°C temperature accuracy
or any combination of the three.
Temperature Total Unadjusted Error
APPLICATIONS
n Measures Voltage, Current, Temperature
n Measures Four Remote Diode Temperatures
n 0.7°C (Typ) Accuracy, 0.06°C Resolution
n 1°C (Typ) Internal Temperature Sensor
n Series Resistance Cancellation
n 14-Bit ADC Measures Voltage/Current
n PWM Temperature Output
n 3V to 5.5V Supply Operating Voltage
n Eight Selectable Addresses
n Internal 10ppm/°C Voltage Reference
n V1 to V8 Inputs ESD Rated to 6kV HBM
n 16-Lead MSOP Package
n Temperature Measurement
n Supply Voltage Monitoring
n Current Measurement
n Remote Data Acquisition
n Environmental Monitoring
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and Easy Drive
is a trademark of Linear Technology Corporation. All other trademarks are the property of their
respective owners.
VCC
2-WIRE
I2C INTERFACE
V1
LTC2991
TAMBIENT
RSENSE
3.3V
5V
1.2V
2.5V
GND
SDA
SCL
ADR0
ADR1
ADR2
3.3V I/O
2.5V I/O
1.2V CORE
FPGA
FPGA
TEMPERATURE
BOARD
TEMPERATURE
V3 V4
V5
V6
V7
V8
PWM TO FAN
V2
2991 TA01a
TAMBIENT (°C)
–50
TERROR (°C)
0.25
0.50
0.75
25 50 75 100 125
2991 TA01b
0
–0.50
–0.25
–25 0 150
–0.75
–1.00
1.00
TREMOTE
TINTERNAL
LTC2991
2
2991ff
For more information www.linear.com/LTC2991
PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC) ................................ 0.3V to 6.0V
Input Voltages V1, V2, V3, V4, V5, V6, V7, V8,
SCL, ADR0, ADR1, ADR2 ..............0.3V to (VCC + 0.3V)
Output Voltage PWM ....................0.3V to (VCC + 0.3V)
Output Voltage SDA ..................................... 0.3V to 6V
Operating Temperature Range
LTC2991C ................................................ 0°C to 70°C
LTC2991I .............................................40°C to 85°C
Storage Temperature Range .................. 65°C to 150°C
Lead Temperature (Soldering, 10 sec)
MS Package .......................................................... 300°C
(Note 1)
1
2
3
4
5
6
7
8
V1
V2
V3
V4
V5
V6
V7
V8
16
15
14
13
12
11
10
9
VCC
ADR2
ADR1
ADR0
PWM
SCL
SDA
GND
TOP VIEW
MS PACKAGE
16-LEAD PLASTIC MSOP
TJMAX = 125°C, θJA = 120°C/W
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LTC2991CMS#PBF LTC2991CMS#TRPBF 2991 16-Lead Plastic MSOP 0°C to 70°C
LTC2991IMS#PBF LTC2991IMS#TRPBF 2991 16-Lead Plastic MSOP –40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
General
VCC Input Supply Range l2.9 5.5 V
ICC Input Supply Current During Conversion, I2C Inactive l1.1 1.5 mA
ISD Input Supply Current Shutdown Mode, I2C Inactive l1 6 µA
VCC(UVL) Input Supply Undervoltage Lockout l1.3 2.0 2.6 V
Measurement Accuracy
TINTERNAL(TUE) Internal Temperature Total Unadjusted Error ±1 ±3.5 °C
TRMT(TUE) Remote Diode Temperature Total Unadjusted
Error η = 1.004 l±0.7 ±1.5 °C
VCC(TUE) VCC Voltage Total Unadjusted Error 2.9V ≤ 5.5V l±0.05 ±0.25 %
VN(TUE) V1 Through V8 Total Unadjusted Error 0V ≤ 4.9V l±0.05 ±0.25 %
VDIFF(TUE) Differential Voltage Total Unadjusted Error
V1 – V2, V3 – V4, V5 – V6, V7 – V8
–300mV≤ VD ≤300mV l±0.1 ±0.75 %
VDIFF(MAX) Full-Scale Differential Voltage l–312.5 312.5 mV
VOFFSET_DIFF Differential Offset V1 through V8 = 0V l–12.5 0 12.5 LSB
VOFFSET_SE Single-Ended Offset V1 through V8 = 0V l–6 0 6 LSB
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted.
LTC2991
3
2991ff
For more information www.linear.com/LTC2991
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VDIFF(CMR) Differential Voltage Common Mode Range l0 VCC V
VLSB(DIFF) Differential Voltage LSB Weight 19.075 µV
VLSB(SINGLE_ENDED) Single-Ended Voltage LSB Weight 305.18 µV
VLSB(TEMP) Temperature LSB Weight Celsius or Kelvin 0.0625 Deg
VLSB(DIODE_VOLTAGE) Diode Voltage LSB Weight Includes Series Resistance IR Drop 38.15 µV
TNOISE Temperature Noise Celsius or Kelvin Filter Disengaged 0.2 °RMS
TNOISE Temperature Noise Celsius or Kelvin Filter Engaged 0.07 °RMS
RES Resolution (No Missing Codes) (Note 2) l14 Bits
INL Integral Nonlinearity 2.9V ≤ VCC ≤ 5.5V, VIN(CM) = 1.5V
(Note 2)
Single-Ended
Differential
l
l
–2
–2
2
2
LSB
LSB
CIN V1 Through V8 Input Sampling Capacitance (Note 2) 0.35 pF
IIN(AVG) V1 Through V8 Input Average Sampling
Current
(0 ≤ VN ≤ 4.9V) (Note 2) 0.6 µA
IDC_LEAK(VIN) V1 Through V8 Input Leakage Current (0 ≤ VN ≤ VCC)l–10 10 nA
PWM
FPWM PWM Period l0.9 1.2 ms
DCPWM Duty Cycle Range l0 99.8 %
SCALEPWM 0% to 100% PWM Temperature Range 32 Deg
Measurement Delay
TINTERNAL, TR1, TR2,
TR3, TR4
Per Configured Temperature
Measurement
l37 46 55 ms
V1, V2, V3, V4, V5,
V6, V7, V8
Single-Ended Voltage Measurement l0.9 1.5 1.8 ms
V1 – V2, V3 – V4,
V5 – V6, V7 – V8
Differential Voltage Measurement l0.9 1.5 1.8 ms
VCC VCC Measurement l0.9 1.5 1.8 ms
Max Delay Mode[4:0] = 11101, TINTERNAL, TR1, TR2, TR3,
TR4 VCC
l277 ms
V1, V3, V5, V7 OUTPUT (Remote Diode Mode Only)
IOUT Output Current Remote Diode Mode l260 350 µA
VOUT Output Voltage l0 VCC V
I2C Interface
VADR(L) ADR Input Low Threshold Voltage Falling l0.3VCC V
VADR(H) ADR Input High Threshold Voltage Rising l0.7VCC V
VOL1 SDA Low Level Maximum Voltage IO = –3mA, VCC 2.9V to 5.5V l0.4 V
VIL Maximum Low Level Input Voltage SDA and SCL Pins l0.3VCC V
VIH Minimum High Level Input Voltage SDA and SCL Pins l0.7VCC V
ISDAI, SCLI SDA, SCL Input Current 0 < VSDA, SCL < VCC l±1 µA
IADR(MAX) Maximum ADR0, ADR1, ADR2 Input Current ADR0, ADR1 or ADR2 Tied to VCC
or GND
l±1 µA
LTC2991
4
2991ff
For more information www.linear.com/LTC2991
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I2C Timing (Note 2)
fSCL(MAX) Maximum SCL Clock Frequency 400 kHz
tLOW Minimum SCL Low Period 1.3 µs
tHIGH Minimum SCL High Period 600 ns
tBUF(MIN) Minimum Bus Free Time Between Stop/Start
Condition
1.3 µs
tHD, STA(MIN) Minimum Hold Time After (Repeated) Start
Condition
600 ns
tSU, STA(MIN) Minimum Repeated Start Condition Set-Up
Time
600 ns
tSU, STO(MIN) Minimum Stop Condition Set-Up Time 600 ns
tHD, DATI(MIN) Minimum Data Hold Time Input 0 ns
tHD, DATO(MIN) Minimum Data Hold Time Output 300 900 ns
tSU, DAT(MIN) Minimum Data Set-Up Time Input 100 ns
tSP(MAX) Maximum Suppressed Spike Pulse
Width
50 250 ns
CXSCL, SDA Input Capacitance 10 pF
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C, VCC = 3.3V, unless otherwise noted.
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: Guaranteed by design and not subject to test.
Note 3: Integral nonlinearity is defined as the deviation of a code from a
straight line passing through the actual endpoints of the transfer curve.
The deviation is measured from the center of the quantization band.
LTC2991
5
2991ff
For more information www.linear.com/LTC2991
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, VCC = 3.3V, unless otherwise noted.
TINTERNAL Error
Remote Diode Error with LTC2991
at 25°C
Remote Diode Error with LTC2991
at Same Temperature as Diode
Supply Current vs TemperatureShutdown Current vs Temperature
Measurement Delay Variation
vs T Normalized to 3.3V, 25°C
VCC TUE Single-Ended VX TUE Differential Voltage TUE
AMBIENT TEMPERATURE (°C)
–50
ICC (µA)
2.0
2.5
3.0
25 50 75 100 125
2991 G01
1.5
1.0
–25 0 150
0.5
0
3.5
VCC = 5V
VCC = 3.3V
AMBIENT TEMPERATURE (°C)
–50
ICC (µA)
1050
1100
1150
25 50 75 100 125
2991 G02
–25 0 150
1000
950
1200
VCC = 5V
VCC = 3.3V
AMBIENT TEMPERATURE (°C)
–50
MEASUREMENT DELAY VARIATION (%)
1
2
3
25 50 75 100 125
2991 G03
–25 0 150
0
–1
4
VCC = 5V
VCC = 3.3V
AMBIENT TEMPERATURE (°C)
–50
VCC TUE (%)
0
25 50 75 100 125
2991 G04
–25 0 150
–0.25
–0.50
0.25
AMBIENT TEMPERATURE (°C)
–50
VX TUE (%)
0
0.25
25 50 75 100 125
2991 G05
–25 0 150
–0.25
–0.50
0.50
AMBIENT TEMPERATURE (°C)
–50
VDIFF TUE (%)
0
25 50 75 100 125
2991 G06
–25 0 150
–0.25
–0.50
0.25
AMBIENT TEMPERATURE (°C)
–50
ERROR (°C)
1.0
1.5
25 50 75 100 125
2991 G07
0.5
0
–25 0 150
–0.5
–1.0
2.0
BATH TEMPERATURE (°C)
–50
LTC2991 TRX ERROR (°C)
0.2
0.4
25 50 75 100 125
2991 G08
0
–0.2
–25 0 150
–0.4
–0.6
0.6
AMBIENT TEMPERATURE (°C)
–50
LTC2991 TRX ERROR (DEG)
0.25
0.50
0.75
25 50 75 100 125
2991 G09
–0.25
0
–25 0 150
–0.50
–1.00
–0.75
1.00
LTC2991
6
2991ff
For more information www.linear.com/LTC2991
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, VCC = 3.3V, unless otherwise noted.
LTC2991 Differential Noise Differential Transfer Function Differential INL
TINTERNAL Noise Remote Diode Noise
LSBs (19.075µV/LSB)
–4
COUNTS
300
400
500 800 READINGS
–1 1
2991 G13
200
100
0
–3 –2 02 3
V1-V2 (V)
–0.4
LTC2991 V1-V2 (V)
0
0.2
0.4
2991 G14
–0.2
–0.4 –0.2 00.2
–0.3 –0.1 0.1 0.3
0.4
–0.1
0.1
–0.3
0.3
VIN (V)
–0.4
INL (LSBs)
0
1
0.4
2991 G15
–1
–2 –0.2 00.2
2
(°C)
–0.75 –0.5
0
COUNTS
200
500
1000 READINGS
–0.25 0.25 0.5
2991 G16
100
400
300
00.75
(°C)
–0.75 –0.5
0
COUNTS
200
600
1000 READINGS
500
–0.25 0.25 0.5
2991 G17
100
400
300
00.75
Single-Ended Transfer Function Single-Ended INL
VX (V)
–1
4
5
2 4
2991 G11
3
2
–0 1 3 5 6
1
0
–1
6
LTC2991 VALUE (V)
VCC = 5V
VCC = 3.3V
VX (V)
0
–1.0
INL (LSBs)
–0.5
0
0.5
1.0
1234
2991 G12
5
VCC = 5V
VCC = 3.3V
Single-Ended Noise
LSBs (305.18µV/LSB)
–3
COUNTS
3500
0
2991 G10
2000
1000
–2 –1 1
500
0
4000 4800 READINGS
3000
2500
1500
2 3
LTC2991
7
2991ff
For more information www.linear.com/LTC2991
Digital Filter Step Response
CPARALLEL (pF)
1
TERROR (°C)
2991 G20
0.4
0.2
010 100 1k 10k 100k 1000k
1.2
1.0
0.8
0.6
TERROR vs CPARALLEL
TERROR vs RSERIES
ITERATION
0
% FULL-SCALE
50
80
200
2991 G18
30
20
050 100 150
100
40
70
60
10
90
RSERIES (Ω)
0
TERROR (°C)
5000
2991 G19
1
0.1 1000 2000 3000 4000
100
10
TYPICAL PERFORMANCE CHARACTERISTICS
TA = 25°C, VCC = 3.3V, unless otherwise noted.
LTC2991
8
2991ff
For more information www.linear.com/LTC2991
PIN FUNCTIONS
V1 (Pin 1): First Monitor Input. This pin can be configured
as a single-ended input (0V to 4.9V) or the positive input
for a differential or remote diode temperature measurement
(in combination with V2). Differential common mode range
is 0V to VCC, ±300mV differential. When configured for
remote diode temperature, this pin will source a current.
V2 (Pin 2): Second Monitor Input. This pin can be config-
ured as a single-ended input (0V to 4.9V) or the negative
input for a differential or remote diode temperature mea-
surement (in combination with V1). Differential common
mode range is 0V to VCC, ±300mV differential. When
configured for remote diode temperature, this pin will have
an internal termination, while the measurement is active.
V3 (Pin 3): Third Monitor Input. This pin can be configured
as a single-ended input (0V to 4.9V) or the positive input
for a differential or remote diode temperature measurement
(in combination with V4). Differential common mode range
is 0V to VCC, ±300mV differential. When configured for
remote diode temperature, this pin will source a current.
V4 (Pin 4): Fourth Monitor Input. This pin can be configured
as a single-ended input (0V to 4.9V) or the negative input
for a differential or remote diode temperature measurement
(in combination with V3). Differential common mode range
is 0V to VCC, ±300mV differential. When configured for
remote diode temperature, this pin will have an internal
termination, while the measurement is active.
V5 (Pin 5): Fifth Monitor Input. This pin can be configured
as a single-ended input (0V to 4.9V) or the positive input
for a differential or remote diode temperature measurement
(in combination with V6). Differential common mode range
is 0V to VCC, ±300mV differential. When configured for
remote diode temperature, this pin will source a current.
V6 (Pin 6): Sixth Monitor Input. This pin can be configured
as a single-ended input (0V to 4.9V) or the negative input
for a differential or remote diode temperature measurement
(in combination with V5). Differential common mode range
is 0V to VCC, ±300mV differential. When configured for
remote diode temperature, this pin will have an internal
termination, while the measurement is active.
V7 (Pin 7): Seventh Monitor Input. This pin can be
configured as a single-ended input (0V to 4.9V) or the
positive input for a differential or remote diode tempera-
ture measurement (in combination with V8). Differential
common mode range is 0V to VCC, ±300mV differential.
When configured for remote diode temperature, this pin
will source a current.
V8 (Pin 8): Eighth Monitor Input. This pin can be configured
as a single-ended input (0V to 4.9V) or the negative input
for a differential or remote diode temperature measurement
(in combination with V7). Differential common mode range
is 0V to VCC, ±300mV differential. When configured for
remote diode temperature, this pin will have an internal
termination, while the measurement is active.
GND (Pin 9): Device Ground. Connect this pin through a
low impedance connection to system ground.
SDA (Pin 10): Serial Bus Data Input and Output. In the
transmitter mode (read), the conversion result is output
through the SDA pin, while in the receiver mode (write),
the device configuration bits are input through the SDA
pin. At data input mode, the pin is high impedance; while
at data output mode, it is an open-drain N-channel driver
and, therefore, an external pull-up resistor or current
source to VCC is needed.
SCL (Pin 11): Serial Bus Clock Input of the I2C Interface.
The LTC2991 can only act as a slave and the SCL pin
only accepts external serial clock. The LTC2991 does not
implement clock stretching.
PWM (Pin 12): PWM Output. The PWM pin provides a
CMOS output level with a duty cycle proportional to the
remote diode temperature of the sensor connected to
pins V7 and V8.
ADR0, ADR1, ADR2 (Pins 13, 14, 15): Serial Bus Address
Control Input. The ADR pins are address control bits for
the device I2C address. See Table 1.
VCC (Pin 16): Chip Power. Connect to 2.9V to 5.5V low
noise supply. A 0.1µF decoupling capacitor to GND is
required for this pin.
LTC2991
9
2991ff
For more information www.linear.com/LTC2991
FUNCTIONAL DIAGRAM
ADC
MUX
MODE
REFERENCE
I2C
UNDERVOLTAGE
DETECTOR
V4
V5
V6
V7 UV
REMOTE
DIODE
SENSORS
POWER
MONITORING
RL
RSENSE
4
V3
3
SCL
2991 FD
V2
2
V1
1
7
6
5
CONTROL
LOGIC
11
SDA 10
PWM 12
ADR0 13
ADR1 14
ADR2 15
GND 9
VCC 16
V8
8
PULSE WIDTH
DETECTOR
VCC
VCC VCC VCC VCC VCC
INTERNAL
SENSOR
+
+
+
VOLTAGE
MONITORING
TIMING DIAGRAM
tSU, DAT
tSU, STO
tSU, STA tBUF
tHD, STA
tSP
tSP
tHD, DATO,
tHD, DATI
tHD, STA
START
CONDITION
STOP
CONDITION
REPEATED START
CONDITION
START
CONDITION
2991 TD
SDAI/SDAO
SCL
LTC2991
10
2991ff
For more information www.linear.com/LTC2991
OPERATION
The LTC2991 monitors voltage, current, internal and remote
temperatures. It can be configured through an I2C inter-
face to measure many combinations of these parameters.
Single or repeated measurements can be configured.
Remote temperature measurements use transistors as
temperature sensors, allowing the remote sensor to be a
discrete NPN (ex. MMBT3904) or an embedded PNP device
in a microprocessor or FPGA. The internal ADC reference
minimizes the number of support components required.
The Functional Diagram displays the main functional com-
ponents of the device. The input signals are selected with an
input mux, controlled by the control logic block. The control
logic block uses the mode bits in the control registers to
manage the sequence and types of data acquisition. The
control logic block also controls the current sources during
remote temperature acquisition. The order of acquisitions
is fixed: V1, V2, V3, V4, V5, V6, V7, V8, TINTERNAL then
VCC. The ADC performs the necessary conversion(s) and
supplies the data to the control logic for routing to the ap-
propriate data register. The I2C interface supplies access
to control, status and data registers. The ADR2, ADR1 and
ADR0 pins select one of eight possible I2C addresses (see
Table 1). The UVLO inhibits I2C communication below the
specified threshold. During an undervoltage condition, the
part is in a reset state, and the data and control registers
are placed in the default state of 00h.
Remote diode measurements are conducted using multiple
ADC conversions and source currents to compensate for
sensor series resistance. The V2, V4, V6 or V8 terminals of
the LTC2991 are terminated with a diode if that channel is
configured for temperature measurements. It is acceptable
to ground these pins, but increased noise may result on
the temperature measurements. The LTC2991 is calibrated
to yield the correct temperature for a remote diode with an
ideality factor of 1.004. See the Applications Information
section for compensation of sensor ideality factors other
than the factory calibrated value of 1.004.
The LTC2991 communicates through an I2C serial in-
terface. The serial interface provides access to control,
status and data registers. I2C defines a 2-wire open-drain
interface supporting multiple slave devices and masters
on a single bus. The LTC2991 supports 100kbit/s in the
standard mode and up to 400kbit/s in fast mode. The
eight physical addresses supported are listed in Table 1.
The I2C interface is used to trigger single conversions, or
start repeated conversions by writing to a dedicated trig-
ger register. The data registers contain a destructive read
status bit (data valid), which is used in repeated mode to
determine if the registers contents have been previously
read. This bit is set when the register is updated with new
data, and cleared when read.
LTC2991
11
2991ff
For more information www.linear.com/LTC2991
The basic LTC2991 application circuit is shown in Figure 1.
APPLICATIONS INFORMATION
Figure 1.
Power Up
The VCC pin must exceed the undervoltage (UV) thresh-
old of 2.5V to keep the LTC2991 out of power-on reset.
Power-on reset will clear all of the data registers and the
control registers.
Temperature Measurements
The LTC2991 can measure internal temperature and up
to four external diode or transistor sensors. During tem-
perature conversion, current is sourced through the V1,
V3, V5 or the V7 pin to forward bias the remote sensing
diode. The change in sensor voltage per degree temperature
change is hundreds of µV/°C, so environmental noise must
be kept to a minimum. Recommended shielding and PCB
trace considerations are illustrated in Figure 2.
The diode equation:
VkT
q
I
I
BE C
S
=
η•ln
(1)
can be solved for T, where T is Kelvin degrees, IS is a
process dependent factor on the order of 1E-13, η is the
diode ideality factor, k is Boltzmann’s constant and q is
the electron charge.
TVq
kInI
I
BE
C
S
=
••η
(2)
The LTC2991 makes differential measurements of diode
voltage to calculate temperature. Proprietary techniques
allow for cancellation of error due to series resistance.
Ideality Factor Scaling
The LTC2991 is calibrated to yield the correct temperature
for a remote diode with an ideality factor of 1.004. While
this value is typical of target sensors, small deviations can
yield significant temperature errors. The ideality factor of
the diode sensor can be considered a temperature scaling
factor. The temperature error for a 1% accurate ideality
factor error is 1% of the Kelvin temperature. Thus, at 25°C,
or 298K, a +1% accurate ideality factor error yields a +2.98
degree error. At 85°C, or 358K, a +1% error yields a 3.6
degree error. It is possible to scale the measured Kelvin
or Celsius temperature measured using the LTC2991 with
a sensor ideality factor other than 1.004, to the correct
value. The scaling Equations (3) and (4), are simple, and
can be implemented with sufficient precision using 16-bit
fixed point math in a microprocessor or microcontroller.
Factory ideality calibration value:
ηCAL = 1.004
Actual sensor ideality value:
ηACT
Figure 2. Recommended PCB Layout
VCC
2-WIRE
I2C INTERFACE
V1
LTC2991
TAMBIENT
RSENSE
3.3V
5V
1.8V
2.5V
GND
SDA
SCL
ADR0
ADR1
ADR2
3.3V I/O
2.5V I/O
1.8V CORE
FPGA
FPGA
TEMPERATURE
BOARD
TEMPERATURE
V3 V4
V5
V6
V7
V8
PWM TO FAN
V2
2991 F01
V1
V2
V3
V4
V5
V6
V7
V8
VCC
ADR2
ADR1
ADR0
PWM
SCL
SDA
GND
LTC2991
2991 F01
GND SHIELD
TRACE
NPN SENSOR
470pF 0.1µF
LTC2991
12
2991ff
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Compensated Kelvin temperature:
TK _ COMP =ηCAL
ηACT
TK _ MEAS
(3)
Compensated Celsius temperature:
CCOMPACT
CAL CMEAS
η
η273.15 273.15
T
T= +
_ _
( )
(4)
A 16-bit unsigned number is capable of representing the
ratio ηCAL/ηACT in a range of 0.00003 to 1.99997, by
multiplying the fractional ratio by 215. The range of scal-
ing encompasses every conceivable target sensor value.
The ideality factor scaling granularity yields a worst-case
temperature error of 0.01° at +125°C. Multiplying this
16-bit unsigned number and the measured Kelvin (un-
signed) temperature represented as a 16-bit number, yields
a 32-bit unsigned result. To scale this number back to a
13-bit temperature (9-bit integer part, and a 4-bit fractional
part), divide the number by 215. Similarly, Celsius coded
temperature values can be scaled using 16-bit fixed-point
arithmetic, using Equation (4). In both cases, the scaled
result will have a 9-bit integer (d[12:4]) and the four LSB’s
(d[3:0]) representing the 4-bit fractional part. To convert
the corrected result to decimal, divide the final result by
24, or 16, as you would the register contents. If ideality
factor scaling is implemented in the target application, it
is beneficial to configure the LTC2991 for Kelvin coded
results to limit the number of math operations required
in the target processor.
T
(UNSIGNED)
KCOMP
ACT
CAL KMEAS
_
_
=
η
η2
2
15
15
(5)
(6)
Sampling Currents
Single-ended voltage measurements are directly sampled
by the internal ADC. The average ADC input current is a
function of the input applied voltage as follows:
ISAMPLE = (VIN – 1.49V) • 0.17[µA/V]
Inputs with source resistance less than 500Ω will yield
full-scale gain errors due to source impedance of < ½ LSB
for 14-bit conversions. The nominal conversion time is
1.5ms for single-ended conversions.
Current Measurements
The LTC2991 has the ability to perform 14-bit current
measurements with the addition of a current sense resis-
tor (see Figure 3).
T
(UNSIGNED) T
CCOMP
ACT
CAL CMEAS
_
_
=
+
(
η
η2273.15 2
15 4
)
2
273 15 2
15
4
– .•
Figure 3. Simplified Current Sense Schematic
In order to achieve 13-bit current sensing a few details
must be considered. Differential voltage or current mea-
surements are directly sampled by the internal ADC. The
average ADC input current for each leg of the differential
input signal during a conversion is:
ISAMPLE = (VIN – 1.49V) • 0.34[µA/V]
The maximum source impedance to yield 14-bit results
with ½ LSB full-scale error is ~50Ω.
In order to achieve 14-bit accuracy, 4-point, or Kelvin
connected measurements of the sense resistor differential
voltage are necessary.
In the case of current measurements, the external sense
resistor is typically small, and determined by the full-scale
input voltage of the LTC2991. The full-scale differential
voltage is 0.300V. The external sense resistance, is then a
function of the maximum measurable current, or REXT_MAX
= 0.300V/IMAX. For example, if you wanted to measure a
V1 V2
LTC2991
0V – VCC
RSENSE
ILOAD
2991 F03
LTC2991
13
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current range of ±5A, the external shunt resistance would
equal 0.300V/5A = 60mΩ.
There exists a way to improve the sense resistors precision
using the LTC2991. The LTC2991 measures both differential
voltage and remote temperature. It is therefore, possible
to compensate for the absolute resistance tolerance of the
sense resistor and the temperature coefficient of the sense
resistor in software. The resistance would be measured
by running a calibrated test current through the discrete
resistor. The LTC2991 would measure both the differential
voltage across this resistor and the resistor temperature.
From this measurement, RO and TO in the following equa-
tion would be known. Using the two equations, the host
microprocessor could compensate for both the absolute
tolerance and the TCR.
RT = RO • [1 + α(T – TO)],where
α = 3930ppm/°C for copper trace
α = ±2 to ~200ppm/°C for discrete R (7)
I = (V1 – V2)/RT (8)
Device Configuration
The LTC2991 is configured by writing the channel control
registers through the serial interface. Refer to Tables 5, 6
and 7 for control register bit definition. The device is ca-
pable of many application configurations including voltage,
temperature and current measurements. It is possible to
configure the device for single or repeated acquisitions. For
repeated acquisitions, only the initial trigger is required,
and new data is written over the old data. Acquisitions
are frozen during serial read data transfers, to prevent the
upper and lower data bytes for a particular measurement
from becoming out of sync. Internally, both the upper and
lower bytes are written at the same instant. Since serial data
transfer timeout is not implemented, failure to terminate a
read operation will yield an indefinitely frozen wait state.
The device can also make single measurements, or with
one trigger, all of the measurements for the configuration.
When the device is configured for multiple measurements,
the order of measurements is fixed. As each new data
result is ready, the MSB of the corresponding data reg-
ister is set, and the corresponding status register bit is
set. These bits are cleared when the corresponding data
register is addressed. The configuration register value at
power-up yields the measurement of the internal tempera-
ture sensor and V1 through V8 as single-ended voltages,
if triggered. The eight input pins V1 through V8 will be in
a high impedance state, until configured otherwise, and a
measurement triggered. Please note that when the device
is configured for remote temperature measurements (using
the control registers 0x06 and/or 0x07), the temperature
data (Trx T) is stored in V1, V3, V5 and V7 respectively
depending on the channel being used. Similarly, during
this configuration the diode voltage (Trx Voltage) is stored
in V2, V4, V6 and V8 registers.
Data Format
The data registers are broken into 8-bit upper and lower
bytes. Voltage and temperature conversions are 13-bits.
The upper bits in the MSB registers provide status on the
resulting conversions. These status bits are different for
temperature and voltage conversions.
Temperature
Temperature conversions are reported as Celsius or Kelvin
results described in Tables 11 and 12, each with 0.0625
degree weighted LSBs. The format is controlled by the
control registers. The temperature MSB result register
most significant bit (Bit 7) is the DATA_VALID bit, which
indicates whether the current register contents have been
accessed since the result was written to the register. This
bit will be set when new data is written to the register,
and cleared when accessed. The LTC2991 internal bias
circuitry maintains this voltage above this level during
normal operating conditions. Bit 4 through bit 0 of the
MSB register are the conversion result bits D[12:8], in
two’s compliment format. Note in Kelvin results, the
result will always be positive. The LSB register contains
temperature result bits D[7:0]. To convert the register
contents to temperature, use the following equation: T =
D[12:0]/16. See Table 16 for conversion value examples.
Remote diode voltage is digitized at ~50µA of bias current.
The ADC LSB value during these conversions is typically
38.15µV. Voltages are only available for the remote diodes,
not the internal sensor. This code repeats at a diode volt-
age of approximately 0.3125V (see Tables 13 and 14).
The absolute temperature of the diode can be used to
detect whether the diode is operating (≤0.3125V or
≥ 0.3125V). This mode is useful for testing small relative
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changes in temperature using the approximate relation-
ship of –2.1mV/°C of voltage dependence on temperature.
With an LSB weight of 38.15µV and a diode temperature
relationship of –2.1mV/°C this yields ~0.018 degree resolu-
tion. For sensor applications involving heaters, the ability
to sense small changes in temperature with low noise
can yield significant power savings, allowing the heater
power to be reduced. Table 16 has some conversion result
examples for various diode voltages.
Voltage/Current
Voltage results are reported in two respective registers,
an MSB and LSB register. The Voltage MSB result register
most significant bit (bit 7) is the DATA_VALID bit, which
indicates whether the current register contents have been
accessed since the result was written to the register. This
bit will be set when the register contents are new, and
cleared when accessed. Bit 6 of the MSB register is the
sign bit, bits 5 though 0 represent bits D[13:8] of the
two’s complement conversion result. The LSB register
holds conversion bits D[7:0]. The LSB value is different
for single-ended voltage measurements V1 through V8,
and differential (current measurements) V1 – V2 , V3 – V4,
V5 – V6 and V7 – V8. Single-ended voltages are limited
to positive values in the range 0V to 4.9V or VCC + 0.2V,
whichever is smaller. Differential voltages can have input
values in the range of –0.300V to 0.300V.
Use the following equations to convert the register values
(see Table 16 for examples):
VSINGLE_ENDED = D[13:0] • 305.18µV
VDIFFERENTIAL = D[13:0] • 19.075µV, if sign = 0
VDIFFERENTIAL = (D[13:0] +1) • –19.075µV, if sign = 1
Current = D[13:0] • 19.075µV/RSENSE, if sign = 0
Current = (D[13:0] +1) • –19.075µV/RSENSE, if sign = 1,
Where RSENSE is the current sensing resistor, typically
< 1Ω.
VCC
The LTC2991 measures VCC. To convert the contents of
the VCC register to voltage, use the following equation:
VCC = 2.5 + (D[13:0] • 305.18µV).
PWM Output
A 9-bit, 1kHz PWM output proportional to temperature V7
is available for controlling fans or heaters. PWM_Thresh-
old is a 9-bit value with an LSB weighting of one degree
Kelvin. PWM_Threshold is subtracted from V7 and a
pulse width proportional to the difference is produced.
Note that the PWM threshold is split among two regis-
ters, with PWM_Threshold[8:1] in register 09h[7:0] and
PWM_Threshold[0] in register 08h[7]. Equation 9 shows
the registers involved. The PWM frequency is ~1kHz. The
PWM output can be disabled or inverted with the PWM
enable and PWM invert bits is register 08h, respectively.
Figure 9 illustrates the PWM transfer function. The equa-
tion for the duty cycle is:
(9)
PWM_DUTY_CYCLE %
(
)
=
100 (REG7 PWM 16)
512
Where REG7 is bits [12:0] and
PWM is PWM Threshold bits [8:0]
A 50% duty cycle PWM signal would occur, for example,
if the PWM threshold was set to 10h (16°C) and register
7 contained 200h (32°C). If channel 7 is configured for
Kelvin temperatures, the PWM threshold must also be a
Kelvin temperature. The registers are two’s compliment
numbers. When calculating the duty cycle above for
Celsius temperatures care should be taken to sign extend
the register 7 and PWM threshold values. For temperatures
below the PWM Threshold, the PWM output pin will be a
constant logic level 0. For temperatures 32 degrees above
Figure 9. PWM Transfer Function
REG7[12:4]-PWM_THRESHOLD[8:0]
PWM DC (%)
50%
16 32
2991 F09
0
0%
99.8%
PWM INVERT = LOGIC 0
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the PWM Threshold, the PWM output pin will be a constant
logic level 1. This relationship is opposite if the PWM
invert bit is set. If the filter is enabled for the V7/V8 pair,
the filtered result is routed to the PWM block; otherwise,
the unfiltered version is used. The PWM CMOS output
drive is intended to be buffered to drive large (>100pF)
external capacitances or resistors <10k. A recommended
noninverting buffer is a NC7SZ125 to increase the drive
capability of the PWM signal.
Digital Filter
Each conversion result can be filtered using an on-chip
digital filter. The filter equation is:
OUTPUT[X] = (15 (OUTPUT[X – 1]) + SAMPLE[X])/16
where output[x] is the register value when enabled. The
filter step response is illustrated in the Typical Perfor-
mance Characteristics section. The filter can be seeded
by triggering an unfiltered conversion of each configured
measurement, then subsequently enabling the filter. This
will cause the filter to converge instantaneously to the value
of the initial unfiltered sample. The filter can be enabled
or disabled for each channel pair and internal temperature
measurements. VCC measurements cannot be filtered.
Digital Interface
The LTC2991 communicates with a bus master using
a 2-wire interface compatible with the I2C Bus and the
SMBus, an I2C extension for low power devices.
The LTC2991 is a read write slave device and supports
SMBus bus read byte data and write byte data, read word
data and write word data commands. The data formats
for these commands are shown in Tables 3 though 15.
The connected devices can only pull the bus wires LOW
and can never drive the bus HIGH. The bus wires are
externally connected to a positive supply voltage via a
current source or pull-up resistor. When the bus is free,
both lines are HIGH. Data on the I2C bus can be transferred
at rates of up to 100kbit/s in the standard mode and up to
400kbit/s in the fast mode. Each device on the I2C bus is
recognized by a unique address stored in that device and
can operate as either a transmitter or receiver, depending
on the function of the device. In addition to transmitters
and receivers, devices can also be considered as masters
or slaves when performing data transfers. A master is
the device which initiates a data transfer on the bus and
generates the clock signals to permit that transfer. At the
same time any device addressed is considered a slave.
The LTC2991 can only be addressed as a slave. Once ad-
dressed, it can receive configuration bits or transmit the
last conversion result. Therefore the serial clock line SCL
is an input only and the data line SDA is bidirectional. The
device supports the standard mode and the fast mode for
data transfer speeds up to 400kbit/s. The Timing Diagram
shows the definition of timing for fast/standard mode
devices on the I2C bus. The internal state machine cannot
update internal data registers during an I2C read operation.
The state machine pauses until the I2C read is complete.
It is therefore, important not to leave the LTC2991 in this
state for long durations, or increased conversion latency
will be experienced.
START and STOP Conditions
When the bus is idle, both SCL and SDA must be high. A
bus master signals the beginning of a transmission with
a START condition by transitioning SDA from high to low
while SCL is high. When the bus is in use, it stays busy
if a repeated START (SR) is generated instead of a STOP
condition. The repeated START (SR) conditions are func-
tionally identical to the START (S). When the master has
finished communicating with the slave, it issues a STOP
condition by transitioning SDA from low to high while SCL
is high. The bus is then free for another transmission.
I2C Device Addressing
Eight distinct bus addresses are configurable using the
ADR0, ADR1 and ADR2 pins. Table 1 shows the corre-
spondence between ADR0, ADR1 and ADR2 pin states and
addresses. There is also one global sync address available
at EEh which provides an easy way to synchronize multiple
LTC2991’s on the same I2C bus. This allows write only access
to all LTC2991’s on the bus for simultaneous triggering.
Acknowledge
The acknowledge signal is used for handshaking between
the transmitter and the receiver to indicate that the last byte
of data was received. The transmitter always releases the
SDA line during the acknowledge clock pulse. When the
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slave is the receiver, it must pull down the SDA line so that
it remains LOW during this pulse to acknowledge receipt
of the data. If the slave fails to acknowledge by leaving
SDA HIGH, then the master can abort the transmission by
generating a STOP condition. After the master has received
the last data bit from the slave, the master must pull down
the SDA line during the next clock pulse to indicate receipt
of the data. After the last byte has been received the master
will leave the SDA line HIGH (not acknowledge) and issue
a STOP condition to terminate the transmission.
Write Protocol
The master begins communication with a START condition
followed by the 7-bit slave address and the RW bit set to
zero. The addressed LTC2991 acknowledges the address
and then the master sends a command byte which indi-
cates which internal register the master wishes to write.
The LTC2991 acknowledges the command byte and then
latches the lower five bits of the command byte into its
internal register address pointer. The master then deliv-
ers the data byte and the LTC2991 acknowledges once
more and latches the data into its internal register. The
transmission is ended when the master sends a STOP
condition. If the master continues sending a second data
byte, as in a write word command, the second data byte
will be acknowledged by the LTC2991 and written to the
next register in sequence, if this register has write access.
Read Protocol
The master begins a read operation with a START condition
followed by the 7-bit slave address and the RW bit set to
zero. The addressed LTC2991 acknowledges this and then
the master sends a command byte which indicates which
internal register the master wishes to read. The LTC2991
acknowledges this and then latches the lower five bits
of the command byte into its internal register address
pointer. The master then sends a repeated START condi-
tion followed by the same seven bit address with the RW
bit now set to one. The LTC2991 acknowledges and sends
the contents of the requested register. The transmission
is ended when the master sends a STOP condition. The
register pointer is automatically incremented after each byte
is read. If the master acknowledges the transmitted data
byte, as in a read word command, the LTC2991 will send
the contents of the next sequential register as the second
data byte. The byte following register 1Dh is register 00h,
or the status register.
Control Registers
The control registers (Tables 5 through 8) determine the
selected measurement mode of the device. The LTC2991 can
be configured to measure voltages, currents and tempera-
tures. These measurements can be single shot or repeated
measurements. Temperatures can be set to report in Celsius
or Kelvin temperature scales. The LTC2991 can be configured
to run particular measurements, or all possible measure-
ments per the configuration specified by the channel enable
register (Table 4). The power-on default configuration of the
control registers is 00h, which translates to a single-ended
voltage measurement of the triggered channels. This mode
prevents the application of remote diode test currents on
pins V1, V3, V5 and V7, and remote diode terminations on
pins V2, V4, V6 and V8 at power-up.
Status Register
The status registers (Tables 3 and 4) report the status of a
particular conversion result. When new data is written into
a particular result register, the corresponding DATA_VALID
bit is set. When the register is addressed by the I2C inter-
face, the status bit (as well as the DATA_VALID bit in the
respective register) is cleared. The host can then determine
if the current available register data is new or stale. The
busy bit, when high, indicates a single shot conversion is
in progress. The busy bit is always high during repeated
mode, after the initial conversion is triggered.
Figure 4. Data Transfer Over I2C or SMBus
STOP
2991 F04
START ADDRESS R/W
P
981-71-71-7
a6-a0 b7-b0 b7-b0
9898
S
DATA DATAACK ACK ACK
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Table 1. I2C Base Address
I2C BASE ADDRESS ADR2 ADR1 ADR0
90h 0 0 0
92h 0 0 1
94h 0 1 0
96h 0 1 1
98h 1 0 0
9Ah 1 0 1
9Ch 1 1 0
9Eh 1 1 1
EEh Global Sync Address
S A A DATAW#ADDRESS COMMAND A
0 0 b7:b001001 a2:a0
FROM MASTER TO SLAVE
XXXXb4:b0 0
2991 F05
P
FROM SLAVE TO MASTER
A: ACKNOWLEDGE (LOW)
A#: NOT ACKNOWLEDGE (HIGH)
R: READ BIT (HIGH)
W#: WRITE BIT (LOW)
S: START CONDITION
P: STOP CONDITION
S A A DATAW#ADDRESS COMMAND A
0 0 b7:b0
DATA
b7:b001001 a2:a0 XXXXb4:b0 0 0
2991 F06
PA
S A A SW#ADDRESS COMMAND A
0 0 1 0
DATA
b7:b001001 a2:a0
ADDRESS
1001 a2:a0XXXXb4:b0 1
2991 F07
PA#R
S A A SW#ADDRESS COMMAND A
0 0 1 0
A
0
DATA
b7:b001001 a2:a0
ADDRESS
1001 a2:a0XXXXb4:b0 1
2991 F08
PA#DATA
b7:b0
R
Figure 5. LTC2991 Serial Bus Write Byte Protocol
Figure 6. LTC2991 Serial Bus Repeated Write Byte Protocol
Figure 7. LTC2991 Serial Bus Read Byte Protocol
Figure 8. LTC2991 Serial Bus Repeated Read Byte Protocol
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Table 2. LTC2991 Register Address and Contents
REGISTER
ADDRESS*
REGISTER NAME
READ/WRITE
DESCRIPTION
00h STATUS LOW R DATA_VALID Bits (V1 Through V8)
01h CH EN, STAT. HI, TRIGGER** R/W CHANNEL ENABLE , VCC, TINTERNAL Conv. Status, Trigger
02h Reserved N/A Reserved
03h Reserved N/A Reserved
04h Reserved N/A Reserved
05h Reserved N/A Reserved
06h V1, V2 and V3, V4 CONTROL R/W V1, V2, V3 and V4 Control Register
07h V5, V6 and V7, V8 CONTROL R/W V5, V6, V7 and V8 Control Register
08h PWM_Threshold(LSB), VCC, TINTERNAL CONTROL R/W PWM Threshold and TINTERNAL Control Register
09h PWM_Threshold(MSB) R/W PWM Threshold
0Ah V1(MSB) R V1 or TR1 T MSB
0Bh V1(LSB) R V1 or TR1 T LSB
0Ch V2(MSB) R V2, V1 – V2, or TR1 Voltage MSB
0Dh V2(LSB) R V2, V1 – V2, or TR1 Voltage LSB
0Eh V3(MSB) R V3, or TR2 T MSB
0Fh V3(LSB) R V3, or TR2 T LSB
10h V4(MSB) R V4, V3 – V4, or TR2 Voltage MSB
11h V4(LSB) R V4, V3 – V4, or TR2 Voltage LSB
12h V5(MSB) R V5, or TR3 T MSB
13h V5(LSB) R V5, or TR3 T LSB
14h V6(MSB) R V6, V5 – V6, or TR3 Voltage MSB
15h V6(LSB) R V6, V5 – V6, or TR3 Voltage LSB
16h V7(MSB) R V7, or TR4 T MSB
17h V7(LSB) R V7, or TR4 T LSB
18h V8(MSB) R V8, V7 – V8, or TR4 Voltage MSB
19h V8(LSB) R V8, V7 – V8, or TR4 Voltage LSB
1Ah TINTERNAL(MSB) R TINTERNAL MSB
1Bh TINTERNAL(LSB) R TINTERNAL LSB
1Ch VCC(MSB) R VCC MSB
1Dh VCC(LSB) R VCC LSB
* Register address MSBs b7 to b5 are ignored.
** Writing any value triggers a conversion.
† Power-on reset sets all registers to 00h.
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Table 3. STATUS LOW (00h) Register
BIT NAME OPERATION
b7 V8, T4, V7 – V8 Ready 1 = V8 Register Contains New Data, 0 = V8 Register Data Old
b6 V7, T4, V7 – V8 Ready 1 = V7 Register Contains New Data, 0 = V7 Register Data Old
b5 V6, T3, V5 – V6 Ready 1 = V6 Register Contains New Data, 0 = V6 Register Data Old
b4 V5, T3, V5 – V6 Ready 1 = V5 Register Contains New Data, 0 = V5 Register Data Old
b3 V4, T2, V3 – V4 Ready 1 = V4 Register Contains New Data, 0 = V4 Register Data Old
b2 V3, T2, V3 – V4 Ready 1 = V3 Register Contains New Data, 0 = V3 Register Data Old
b1 V2, T1, V1 – V2 Ready 1 = V2 Register Contains New Data, 0 = V2 Register Data Old
b0 V1, T1, V1 – V2 Ready 1 = V1 Register Contains New Data, 0 = V1 Register Data Old
Table 4. STATUS HIGH, CHANNEL ENABLE (01h) Register (Default 00h)
BIT NAME R/W OPERATION
b7 V7 and V8, V7 – V8, TR4 Enable R/W 1 = V7 and V8, or V7 – V8 or T4 Enabled
0 = V7 and V8, or V7 – V8 or T4 Disabled (Default)
b6 V5 and V6, V5 – V6, TR3 Enable R/W 1 = V5 and V6, or V5 – V6 or T3 Enabled
0 = V5 and V6, or V5 – V6 or T3 Disabled (Default)
b5 V3 and V4, V3 – V4, TR2 Enable R/W 1 = V3 and V4, or V3 – V4 or T2 Enabled
0 = V3 and V4, or V3 – V4 or T2 Disabled (Default)
b4 V1 and V2, V1 – V2, TR1 Enable R/W 1 = V1 and V2, or V1 – V2 or T1 Enabled
0 = V1 and V2, or V1 – V2 or T1 Disabled (Default)
b3 TINTERNAL VCC Enable R/W 1 = TINTERNAL and VCC Enabled
0 = TINTERNAL and VCC Disabled (Default)
b2 BUSY R 1 = A Conversion Is in Process
0 = Sleep Mode (Default)
b1 TINTERNAL R 1 = TINTERNAL Register Contains New Data
0 = TINTERNAL Register Data Old (Default)
b0 VCC R 1 = VCC Register Contains New Data
0 = VCC Register Data Old (Default)
Table 5. V1, V2 and V3, V4 CONTROL (06h) Register (Default 00h)
BIT NAME OPERATION
b7 V3, V4 Filt 1 = Filter Enabled, 0 = Filter Disabled for V3 and V4, V3 – V4 or T2 (Default)
b6 TR2 Kelvin 1 = Kelvin, 0 = Celsius for T2 (Default)
b5 V3, V4 Temperature 1 = Temperature, 0 = Voltage (Per b4 Setting) (Default)
b4 V3, V4 Differential 1 1 = Differential (V3 – V4) and V3 Single-Ended
0 = Single-Ended Voltage (V3 and V4) (Default)
b3 V1, V2 Filt 1 = Filter Enabled, 0 = Filter Disabled for V1 and V2, V1 – V2 or T1 (Default)
b2 TR1 Kelvin 1 = Kelvin, 0 = Celsius for T1 (Default)
b1 V1, V2 Temperature 1 = Temperature, 0 = Voltage (Per b0 Setting) (Default)
b0 V1, V2 Differential 1 = Differential (V1 – V2) and V1 Single-Ended
0 = Single-Ended Voltage (V1 and V2) (Default)
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Table 6. V5, V6 and V7, V8 CONTROL (07h) Register (Default 00h)
BIT NAME OPERATION
b7 V7, V8 Filt 1 = Filter Enabled, 0 = Filter Disabled for V7 and V8, V7 – V8 or T4 (Default)
b6 TR4 Kelvin 1 = Kelvin, 0 = Celsius for T4 (Default)
b5 V7, V8 Temperature 1 = Temperature, 0 = Voltage (Per b4 Setting) (Default)
b4 V7, V8 Differential 1 = Differential (V7 – V8) and V7 Single-Ended
0 = Single-Ended Voltage (V7 and V8) (Default)
b3 V5, V6 Filt 1= Filter Enabled, 0 = Filter Disabled for V5 and V6, V5 – V6 or T3 (Default)
b2 TR3 Kelvin 1 = Kelvin, 0 = Celsius for T3 (Default)
b1 V5, V6 Temperature 1 = Temperature, 0 = Voltage (Per b0 Setting) (Default)
b0 V5, V6 Differential 1 = Differential (V5 – V6) and V5 Single-Ended
0 = Single-Ended Voltage (V5 and V6) (Default)
Table 7. PWM, VCC and TINTERNAL CONTROL (08h) Register (Default 00h)
BIT NAME OPERATION
b7 PWM[0] PWM Threshold Least Significant Bit (Default = 0)
b6 PWM Invert* 1 = PWM Inverted, 0 = PWM Noninverted (Default)
b5 PWM Enable** 1 = PWM Enabled, 0 = PWM Disabled (Default)
b4 Repeated Acquisition 1 = Repeated Mode
0 = Single Shot (Default)
b3 TINTERNAL Filt 1 = Filter Enabled for TINTERNAL
0 = Filter Disabled TINTERNAL (Default)
b2 TINTERNAL Kelvin 1 = Kelvin, 0 = Celsius for TINTERNAL (Default)
b1 Reserved Reserved
b0 Reserved Reserved
* Noninverted would be an increasing duty cycle for an increasing temperature.
** If disabled and noninverted, the PWM pin will be a logic level 0. If disabled and inverted, the PWM pin will be a logic level 1.
Table 8. PWM Register Format (Default 00h)
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
D8 D7 D6 D5 D4 D3 D2 D1
Note: D0 is located in the MSB of PWM, VCC and TINTERNAL CONTROL (08h) Register
Table 9. Voltage/Current Measurement MSB Data Register Format
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
DV* Sign D13 D12 D11 D10 D9 D8
*Data valid is set when a new result is written into the register. Data valid is cleared
when this register is addressed (read) by the I2C interface.
Table 10. Voltage/Current Measurement LSB Data Register Format
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
D7 D6 D5 D4 D3 D2 D1 D0
LTC2991
21
2991ff
For more information www.linear.com/LTC2991
Table 11. Temperature Measurement MSB Data Register Format
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
DV* X X D12 D11 D10 D9 D8
*Data valid is set when a new result is written into the register. Data valid is cleared
when this register is addressed (read) by the I2C interface.
X Unused
Table 12. Temperature Measurement LSB Data Register Format
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
D7 D6 D5 D4 D3 D2 D1 D0
Table 14. Diode Voltage Measurement LSB Data Register Format
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
D7 D6 D5 D4 D3 D2 D1 D0
Table 13. Diode Voltage Measurement MSB Data Register Format
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
DV* X X D12 D11 D10 D9 D8
*Data valid is set when a new result is written into the register. Data valid is cleared
when this register is addressed (read) by the I2C interface.
X Unused
Table 15. PWM Threshold Register Format
Bit7 Bit6 Bit5 Bit4 Bit3 Bit2 Bit1 Bit0
D7 D6 D5 D4 D3 D2 D1 D0
D7:D0 = PWM[8:1], bit 0 is located in the PWM, VCC and TINT CONTROL Register (Table 7)
Table 16. Conversion Formats
VOLTAGE FORMATS SIGN BINARY VALUE D[13:0] VOLTAGE
Single-Ended
LSB = 305.18µV = 2.5/213 0 11111111111111 >5
0 10110011001101 3.5000
0 01111111111111 2.5000
0 00000000000000 0.0000
1 11110000101001 –0.3000
Differential
LSB = 19.075µV = 2.5/217 0 11110101101111 0.300
0 10000010001111 0.159
0 00000000000000 0.0000
1 01111101110001 –0.159
1 00001010010001 –0.300
VCC = Result + 2.5V
LSB = 305.18µV = 2.5/213 0 10110011001101 VCC = 6.0
0 10000000000000 VCC = 5.0
0 00001010001111 VCC = 2.7
APPLICATIONS INFORMATION
LTC2991
22
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For more information www.linear.com/LTC2991
APPLICATIONS INFORMATION
Table 17. Recommended Transistors to Be Used as Temperature Sensors
MANUFACTURER PART NUMBER PACKAGE
Fairchild Semiconductor MMBT3904 SOT-23
Fairchild Semiconductor FMMT3904 SOT-23
Fairchild Semiconductor 2N3904 TO-92
Central Semiconductor CMPT3904 SOT-23
Central Semiconductor CET3904E SOT-883L
Diodes, Inc. MMBT3904 SOT-23
On Semiconductor MMBT3904LT1 SOT-23
NXP MMBT3904 SOT-23
Infineon MMBT3904 SC-70
Rohm UMT3904 SOT-23
Table 16. Conversion Formats
TEMPERATURE FORMATS FORMAT BINARY VALUE D[12:0] TEMPERATURE
Temperature Internal, TR1 Through TR4
LSB = 0.0625 Degrees
Celsius 0011111010000 125.0000
Celsius 0000110010001 25.0625
Celsius 0000110010000 25.0000
Celsius 1110110000000 –40.0000
Kelvin 1100011100010 398.1250
Kelvin 1000100010010 273.1250
Kelvin 0111010010010 233.1250
Kelvin 0010011010000 77.0000
DIODE VOLTAGE FORMATS Sign Binary Value D[12:0] Voltage
Diode Voltage TR1 Through TR4
LSB = 38.15µV
0 0000000000000 0.0000
0 1111111111111 0.31249
0 0000000000000 0.31252
0 1111111111111 0.62501
0 0000000000000 0.62505
0 1001100110010 0.99999
LTC2991
23
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For more information www.linear.com/LTC2991
High Voltage/Current and Temperature Monitoring
TYPICAL APPLICATIONS
+
–INS 0.1µF
VIN
5V TO 105V
0.1µF
ALL CAPACITORS ±20%
OTHER APPS
VOLTAGE, CURRENT AND TEMPERATURE CONFIGURATION:
CONTROL REGISTER: 0x06 0xA0
TAMBIENT REG 1A, 1B: 0.0625°C/LSB
VLOAD REG 0A, 0B: 13.2mV/LSB
V2(ILOAD) REG 0C, 0D: 1.223mA/LSB
TPROCESSOR REG 0E, 0F: 0.0625°C/LSB
VCC REG 1C, 1D: 2.5V + 305.18µV/LSB
MMBT3904
RIN
20Ω
1%
ILOAD
0A TO 10A
ROUT
4.99k
1%
200k
1%
4.75k
1% 0.1µF
RSENSE = 1mΩ
1%
–INF
V+
V
LTC6102HV
OUT
VREG
+IN
VCC V1
LTC2991
2-WIRE I2C
INTERFACE
5V
GND
SDA
SCL
ADR0
ADR1
ADR2
V3
V4
V5 TO V8
V2
2991 TA02
4
LTC2991
24
2991ff
For more information www.linear.com/LTC2991
TYPICAL APPLICATIONS
Computer Voltage and Temperature Monitoring
Motor Protection/Regulation
MICROPROCESSOR
VCC V1
LTC2991
2-WIRE I2C
INTERFACE
GND
SDA
SCL
ADR0
ADR1
ADR2
V3
V4
V2
2991 TA03
10k
1%
10k
1%
10k
1%
3.3V
30.1k
1%
5V
12V
VOLTAGE AND TEMPERATURE CONFIGURATION
CONTROL REGISTER: 0x06 0x0A
TAMBIENT REG 1A, 1B: 0.0625°C/LSB
V1(+5) REG 0A, 0B: 610µV/LSB
V2(+12) REG 0C, 0D: 1.22mV/LSB
TPROCESSOR REG 0E, 0F: 0.0625°C/LSB
VCC REG 1C, 1D: 2.5V + 305.18µV/LSB
0.1µF
OTHER APPS
V5 TO V8
4
VCC V1
LTC2991
LOADPWR = I • V
0.1Ω
1%
MOTOR CONTROL VOLTAGE
0VDC TO 5VDC
0A TO ±2.2A
2-WIRE I2C
INTERFACE
5V
GND
TMOTOR
MMBT3904
SDA
SCL
ADR0
ADR1
ADR2
V3
V4
V2
2991 TA04
MOTOR
TAMBIENT
VOLTAGE, CURRENT AND TEMPERATURE CONFIGURATION:
CONTROL REGISTER: 0x06: 0xA1
TAMBIENT REG 1A, 1B: 0.0625°C/LSB
VMOTOR REG 0A, 0B: 305.18µV/LSB
IMOTOR REG 0C, 0D: 190.75µA/LSB
TMOTOR REG 1A, 1B: 0.0625°C/LSB
VCC REG 1C, 1D: 2.5V + 305.18µV/LSB
OTHER APPS
V5 TO V8
4
LTC2991
25
2991ff
For more information www.linear.com/LTC2991
TYPICAL APPLICATIONS
Large Motor Protection/Regulation
Fan/Air Filter/Temperature Alarm
VCC V1
LTC2991
LOADPWR = I • V
0.01Ω
1W, 1%
MOTOR CONTROL VOLTAGE
0V TO 40V
0A TO 10A
2-WIRE I2C
INTERFACE
5V
71.5k
1%
71.5k
1%
10.2k
1%
10.2k
1%
GND
TMOTOR
MMBT3904
SDA
SCL
ADR0
ADR1
ADR2
V3
V4
V2
2991 TA05
MOTOR
TAMBIENT
VOLTAGE, CURRENT AND TEMPERATURE CONFIGURATION:
CONTROL REGISTER 06: 0xA1
TAMBIENT REG 1A, 1B: 0.0625°C/LSB
VMOTOR REG 0A, 0B: 2.44mV/LSB
IMOTOR REG 0C, 0D: 15.54mA/LSB
TMOTOR REG 0E, 0F: 0.0625°C/LSB
VCC REG 1C, 1D: 2.5V + 305.18µV/LSB
OTHER APPS
V5 TO V8
4
VCC V1
LTC2991
2-WIRE I2C
INTERFACE
3.3V
GND
22Ω
0.125W
HEATER
NDS351AN
TEMPERATURE FOR:
HEATER ENABLE
GOOD FAN
BAD FAN
FAN
MMBT3904
MMBT3904
SDA
SCL
ADR0
ADR1
V3
V4
V2
2991 TA06
TAMBIENT HEATER ENABLE
2 SECOND PULSE
CONTROL REGISTER 0x06 = 0xAA
TAMBIENT REG 1A, 1B: 0.0625°C/LSB
TFAN1 REG 0A, 0B: 0.0625°C/LSB
TFAN2 REG 0C, 0D: 0.0625°C/LSB
VCC REG 1C, 1D: 2.5V + 305.18µV/LSB
3.3V
22Ω
0.125W
FAN
OTHER APPS
V5 TO V8
4
LTC2991
26
2991ff
For more information www.linear.com/LTC2991
TYPICAL APPLICATIONS
Battery Monitoring
Wet Bulb Psychrometer
REFERENCES
http://en.wikipedia.org/wiki/Hygrometer
http://en.wikipedia.org/wiki/Psychrometrics
VCC V1
LTC2991
5V
µC
GND TDRY TWET
MMBT3904 MMBT3904
SDA
SCL
ADR0
ADR1
ADR2
V3
V4
V2
2991 TA08
470pF
TAMBIENT
DAMP MUSLIN
WATER
RESERVOIR
CONTROL REGISTER 0x06 = 0xAA
TAMBIENT REG 1A, 1B: 0.0625°C/LSB
TWET REG 0A, 0B: 0.0625°C/LSB
TDRY REG 0C, 0D: 0.0625°C/LSB
VCC REG 1C, 1D: 2.5V + 305.18µV/LSB
T
NDS351AN
FAN ENABLE
5V
FAN
FAN: SUNON
KDE0504PFB2
OTHER APPS
V5 TO V8
4
VCC V1
LTC2991
BATTERY I AND V MONITOR
0.1Ω*
CHARGING
CURRENT
2-WIRE I2C
INTERFACE
5V
GND
NiMH
BATTERY
V(t)
100% 100%
• • •
TBATT
MMBT3904
SDA
SCL
ADR0
ADR1
ADR2
V3
V4
V2
2991 TA07
TAMBIENT
*IRC LRF3W01R015F
VOLTAGE AND TEMPERATURE CONFIGURATION:
CONTROL REGISTER: 0xA1
TAMBIENT REG 1A, 1B: 0.0625°C/LSB
VBAT REG 0A, 0B: 305.18µV/LSB
IBAT REG 0C, 0D: 190.75µA/LSB
TBAT REG 0E, 0F: 0.0625°C/LSB
VCC REG 1C, 1D: 2.5V + 305.18µV/LSB
+T(t)
100%
I(t)
OTHER APPS
V5 TO V8
4
LTC2991
27
2991ff
For more information www.linear.com/LTC2991
TYPICAL APPLICATIONS
Wind Direction/Instrumentation
VCC V1
LTC2991
3.3V
µC
GND
MMBT3904 MMBT3904
SDA
SCL
ADR0
ADR1
ADR2
V3
V4
V2
2991 TA10
3.3V
HEATER
75Ω
0.125W
TAMBIENT
CONTROL REGISTER 0x06 0xAA
TAMBIENT REG 1A, 1B 0.0625°C/LSB
TR1 REG 0A, 0B 0.0625°C/LSB
TR2 REG 0E, 0F 0.0625°C/LSB
VCC REG 1C, 1D 2.5V + 305.18µV/LSB
2N7002
HEATER ENABLE
2 SECOND PULSE
OTHER APPS
V5 TO V8
4
Liquid Level Indicator
VCC
LTC2991
3.3V
µC
GND
SDA
SCL
ADR0
ADR1
ADR2
V1
V4
V3
V2
3.3V
TAMBIENT
CONTROL REGISTER 0x06 = 0xAA
TAMBIENT REG 1A, 1B: 0.0625°C/LSB
TDRY REG 0A, 0B: 0.0625°C/LSB
TWET REG 0C, 0D: 0.0625°C/LSB
VCC REG 1C, 1D: 2.5V + 305.18µV/LSB
NDS351AN
2991 TA09
*HEATER: 75Ω 0.125W
*SENSOR MMBT3904, DIODE CONNECTED
SENSOR LO*
T = ~2.0°C pp, SENSOR HI
~0.2°C pp, SENSOR LO
SENSOR HI*
HEATER ENABLE
2 SECOND PULSE
HEATER ENABLE
SENSOR HI
SENSOR LO
OTHER APPS
V5 TO V8
4
LTC2991
28
2991ff
For more information www.linear.com/LTC2991
Oven Control with Power Monitor
Remote Temperature Sensing with Extended ESD Performance
VCC
2-WIRE
I2C INTERFACE
V1
LTC2991
TAMBIENT
5V
GND
SDA
SCL
ADR0
ADR1
ADR2
V3
V4
V5
V6
OTHER APPLICATIONS
VOLTAGE AND CURRENT (POWER) MONITOR
OVEN
TSET 70°C
TEMPERATURE
SENSOR
HEATER
VCC
V7
V8
PWM
V2
2991 TA11
+
100k
F
LT6240
100k
1M
VCC
5V
VOLTAGE, CURRENT, TEMPERATURE AND PWM CONFIGURATION:
CONTROL REGISTER 0x06: 0x01
TAMBIENT REG 1A, 1B 0.0625°C/LSB
VHEATER REG 0A, 0B 305µV/LSB
IHEATER REG 0C, 0D 19.075µV/RHEATERA/LSB
TOVEN REG 16, 17 0.0625°C/LSB
VCC REG 1C, 1D 2.5V + 305.18µV/LSB
0x07: 0xA0
PWM, TINTERNAL, VCC REG:
PWM REGISTER
0x08: 0x50
0x09: 0x1B
VCC
LTC2991
3.3V
GND
SDA
SCL
V1
V2
500Ω
500Ω
2991 TA13
CONTROL REGISTER 0x06 = 0xAA
REMOTE TEMPERATURE SENSOR REG OB, OB: 0.0625 °C/LSB
MMBT3904
> 8kV ESD
MMBT3904
REMOTE
TEMPERATURE
SENSOR
PROTECTION
DEVICE
TYPICAL APPLICATIONS
LTC2991
29
2991ff
For more information www.linear.com/LTC2991
VCC
LTC2991
3.3V
GND
SDA
SCL
SDA
SCL
V1
V2
1, 4
9
10
S0, S1
LTC1393
S2, S3
2, 3
5, 8
6, 7
2991 TA14
LTC2291 REMOTE TEMPERATURE SENSOR REG OB, OB: 0.0625 °C/LSB
LTC2991 CONTROL REGISTER 0x06 0xAA
LTC1393 CONTROL BYTE SENSOR A = 0x0B
LTC1393 CONTROL BYTE SENSOR B = 0x0A
LTC1393 CONTROL BYTE SENSOR C = 0x0C
LTC1393 CONTROL BYTE SENSOR D = 0x0E
LTC1393
WIRED AS A DUAL
CROSS-POINT SWITCH
MMBT3904MMBT3904
WIRE PAIR 1
REMOTE
TEMPERATURE
SENSOR A
REMOTE
TEMPERATURE
SENSOR B
MMBT3904MMBT3904
WIRE PAIR 2
REMOTE
TEMPERATURE
SENSOR C
REMOTE
TEMPERATURE
SENSOR D
QUAD Remote Temperature Sensing with Two Wire Pairs Using One LTC2991 Channel
TYPICAL APPLICATIONS
LTC2991
30
2991ff
For more information www.linear.com/LTC2991
PACKAGE DESCRIPTION
Please refer to http://www.linear.com/product/ltc2991#packaging for the most recent package drawings.
MSOP (MS16) 0213 REV A
0.53 ±0.152
(.021 ±.006)
SEATING
PLANE
0.18
(.007)
1.10
(.043)
MAX
0.17 –0.27
(.007 – .011)
TYP
0.86
(.034)
REF
0.50
(.0197)
BSC
16151413121110
12345678
9
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.254
(.010) 0° – 6° TYP
DETAIL “A”
DETAIL “A”
GAUGE PLANE
5.10
(.201)
MIN
3.20 – 3.45
(.126 – .136)
0.889 ±0.127
(.035 ±.005)
RECOMMENDED SOLDER PAD LAYOUT
0.305 ±0.038
(.0120
±.0015)
TYP
0.50
(.0197)
BSC
4.039 ±0.102
(.159 ±.004)
(NOTE 3)
0.1016 ±0.0508
(.004 ±.002)
3.00 ±0.102
(.118 ±.004)
(NOTE 4)
0.280 ±0.076
(.011 ±.003)
REF
4.90 ±0.152
(.193 ±.006)
MS Package
16-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1669 Rev A)
LTC2991
31
2991ff
For more information www.linear.com/LTC2991
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-
tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
A 10/11 Corrected axis label on Figure 9.
Inserted new text in I2C Device Addressing section.
Inserted new row in Table 1.
Revised component values in Typical Application drawing TA05.
14
15
17
25
B 07/13 Corrected diode voltage value.
Corrected VDIFFERENTIAL and current equations.
13
14
C 10/13 Corrected slave address in Figures 5, 6, 7 and 8. 17
D 03/14 Corrected LSB size to 19.075µV/LSB and 190.75µA/LSB. 6, 24, 26,
28, 32
E 08/15 Added Single-Ended and Differential VOFFSET.
Inserted new text in Device Configuration.
Updated MSOP Package Description to Rev A.
2
13
30
F 10/15 Correct serial bus protocol.
Correct Table 16.
16
22
LTC2991
32
2991ff
For more information www.linear.com/LTC2991
LINEAR TECHNOLOGY CORPORATION 2011
LT 1015 REV F • PRINTED IN USA
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com/LTC2991
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LTC2997 Remote/Internal Temperature Sensor Temperature to Voltage with Integrated 1.8V Voltage Reference, ±1°C Accuracy
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with EEPROM
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0.1°C Accuracy, Directly Digitize RTDs, Thermocouples, Thermistors and Diodes, 20
Flexible Inputs
Parasitic Resistance Voltage and Current Monitoring with Temperature Compensation
VCC V1
2.1k 2.1k
LTC2991
INDUCTOR WITH
RPARASITIC
RPARASITIC ~ 4000ppm/°C
ILOAD
BUCK
REGULATOR
2-WIRE I2C
INTERFACE
5V
GND
THERMAL
COUPLING
CONTROL REGISTER 0x06: 0xA1:
TAMBIENT REG 1A, 1B: 0.0625°C/LSB
VLOAD REG 0A, 0B: 305µV/LSB
ILOAD REG 0C, 0D: 190.75µA/LSB
TRPARASITIC REG 1A, 1B: 0.0625°C/LSB
VCC REG 1C, 1D: 2.5V + 305.18µV/LSB
QUIET NODE
SWITCHING
WAVEFORM
MMBT3904
VOLTAGE, CURRENT AND TEMPERATURE CONFIGURATION
SDA
SCL
ADR0
ADR1
ADR2
V3
V4
V2
2991 TA12
TAMBIENT
F
F
F
OTHER APPS
V5 TO V8
4
F
5V