1
2
3
4
5
6
7
8 9
10
11
12
13
14
15
16
CS SCLK
VADOUT
AGND DIN
IN0 VD
IN1 DGND
IN2 IN7
IN3 IN6
IN4 IN5
ADC108S052
ADC108S052
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ADC108S052 8-Channel, 200 ksps to 500 ksps, 10-Bit A/D Converter
Check for Samples: ADC108S052
1FEATURES DESCRIPTION
The ADC108S052 is a low-power, eight-channel
23 Eight Input Channels CMOS 10-bit analog-to-digital converter specified for
Variable Power Management conversion throughput rates of 200 ksps to 500 ksps.
Independent Analog and Digital Supplies The converter is based on a successive-
approximation register architecture with an internal
SPI™/ QSPI™/MICROWIRE/DSP Compatible track-and-hold circuit. It can be configured to accept
Packaged in 16-Lead TSSOP up to eight input signals at inputs IN0 through IN7.
The output serial data is straight binary and is
KEY SPECIFICATIONS compatible with several standards, such as SPI™,
Conversion Rate: 200 ksps to 500 ksps QSPI™, MICROWIRE, and many common DSP
DNL (VA= VD= 2.7V to 5.0V): ±0.4 LSB (max) serial interfaces.
INL (VA = VD = 2.7V to 5.0V): ±0.4 LSB (max) The ADC108S052 may be operated with independent
Power Consumption: analog and digital supplies. The analog supply (VA)
can range from +2.7V to +5.25V, and the digital
3V Supply: 1.5 mW (typ) supply (VD) can range from +2.7V to VA. Normal
5V Supply: 7.5 mW (typ) power consumption using a +3V or +5V supply is 1.5
mW and 7.5 mW, respectively. The power-down
APPLICATIONS feature reduces the power consumption to 0.09 µW
using a +3V supply and 0.30 µW using a +5V supply.
Automotive Navigation The ADC108S052 is packaged in a 16-lead TSSOP
Portable Systems package. Operation over the extended industrial
Medical Instruments temperature range of 40°C to +105°C is ensured.
Mobile Communications
Instrumentation and Control Systems
Connection Diagram
Figure 1. TSSOP Package
See Package Number PW0016A
1Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
2SPI, QSPI are trademarks of Motorola, Inc..
3All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date. Copyright © 2005–2013, Texas Instruments Incorporated
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
IN0
IN7
MUX T/H
ADC108S052 SCLK
VA
AGND
DGND
VD
CS
DIN
DOUT
CONTROL
LOGIC
10-BIT
SUCCESSIVE
APPROXIMATION
ADC
.
.
.
AGND
ADC108S052
SNAS337G SEPTEMBER 2005REVISED MARCH 2013
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Block Diagram
Pin Descriptions and Equivalent Circuits
Pin No. Symbol Equivalent Circuit Description
ANALOG I/O
4 - 11 IN0 to IN7 Analog inputs. These signals can range from 0V to VREF.
DIGITAL I/O
Digital clock input. The specified performance range of frequencies
16 SCLK for this input is 3.2 MHz to 8 MHz. This clock directly controls the
conversion and readout processes.
Digital data output. The output samples are clocked out of this pin on
15 DOUT the falling edges of the SCLK pin.
Digital data input. The ADC108S052's Control Register is loaded
14 DIN through this pin on rising edges of the SCLK pin.
Chip select. On the falling edge of CS, a conversion process begins.
1 CS Conversions continue as long as CS is held low.
POWER SUPPLY
Positive analog supply pin. This voltage is also used as the
reference voltage. This pin should be connected to a quiet +2.7V to
2 VA+5.25V source and bypassed to GND with 1 µF and 0.1 µF
monolithic ceramic capacitors located within 1 cm of the power pin.
Positive digital supply pin. This pin should be connected to a +2.7V
13 VDto VAsupply, and bypassed to GND with a 0.1 µF monolithic ceramic
capacitor located within 1 cm of the power pin.
3 AGND The ground return for the analog supply and signals.
12 DGND The ground return for the digital supply and signals.
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These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
Absolute Maximum Ratings(1)(2)
Analog Supply Voltage VA0.3V to 6.5V
Digital Supply Voltage VD0.3V to VA+ 0.3V, max 6.5V
Voltage on Any Pin to GND 0.3V to VA+0.3V
Input Current at Any Pin(3) ±10 mA
Package Input Current(3) ±20 mA
Power Dissipation at TA= 25°C See(4)
ESD Susceptibility(5) Human Body Model 2500V
Machine Model 250V
For soldering specifications: http://www.ti.com/lit/SNOA549
Junction Temperature +150°C
Storage Temperature 65°C to +150°C
(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. For ensured specifications and test conditions, see the
Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance characteristics may
degrade when the device is not operated under the listed test conditions.
(2) If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
(3) When the input voltage at any pin exceeds the power supplies (that is, VIN < AGND or VIN > VAor VD), the current at that pin should be
limited to 10 mA. The 20 mA maximum package input current rating limits the number of pins that can safely exceed the power supplies
with an input current of 10 mA to two.
(4) The absolute maximum junction temperature (TJmax) for this device is 150°C. The maximum allowable power dissipation is dictated by
TJmax, the junction-to-ambient thermal resistance (θJA), and the ambient temperature (TA), and can be calculated using the formula
PDMAX = (TJmax TA)/θJA. In the 16-pin TSSOP, θJA is 96°C/W, so PDMAX = 1,200 mW at 25°C and 625 mW at the maximum
operating ambient temperature of 105°C. Note that the power consumption of this device under normal operation is a maximum of 12
mW. The values for maximum power dissipation listed above will be reached only when the ADC108S052 is operated in a severe fault
condition (e.g. when input or output pins are driven beyond the power supply voltages, or the power supply polarity is reversed).
Obviously, such conditions should always be avoided.
(5) Human body model is 100 pF capacitor discharged through a 1.5 kΩresistor. Machine model is 220 pF discharged through ZERO ohms
Operating Ratings(1)(2)
Operating Temperature 40°C TA+105°C
VASupply Voltage +2.7V to +5.25V
VDSupply Voltage +2.7V to VA
Digital Input Voltage 0V to VA
Analog Input Voltage 0V to VA
Clock Frequency 50 kHz to 16 MHz
(1) Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings indicate conditions for
which the device is functional, but do not ensure specific performance limits. For ensured specifications and test conditions, see the
Electrical Characteristics. The ensured specifications apply only for the test conditions listed. Some performance characteristics may
degrade when the device is not operated under the listed test conditions.
(2) All voltages are measured with respect to GND = 0V, unless otherwise specified.
Package Thermal Resistance
Package θJA
16-lead TSSOP on 4-layer, 2 oz. PCB 96°C / W
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ADC108S052 Converter Electrical Characteristics(1)
The following specifications apply for VA= VD= +2.7V to +5.25V, AGND = DGND = 0V, fSCLK = 3.2 MHz to 8 MHz, fSAMPLE =
200 ksps to 500 ksps, and CL= 50pF, unless otherwise noted. Boldface limits apply for TA= TMIN to TMAX: all other limits TA
= 25°C. Limits
Parameter Test Conditions Typ Units
(2)
STATIC CONVERTER CHARACTERISTICS
Resolution with No Missing Codes 10 Bits
Integral Non-Linearity (End Point
INL ±0.1 ±0.4 LSB (max)
Method)
DNL Differential Non-Linearity ±0.2 ±0.4 LSB (min)
VOFF Offset Error +0.3 ±0.7 LSB (max)
OEM Offset Error Match ±0.06 ±0.4 LSB (max)
FSE Full Scale Error +0.1 ±0.4 LSB (max)
FSEM Full Scale Error Match ±0.06 ±0.4 LSB (max)
DYNAMIC CONVERTER CHARACTERISTICS
FPBW Full Power Bandwidth (3dB) 8 MHz
SINAD Signal-to-Noise Plus Distortion Ratio fIN = 40.2 kHz, 0.02 dBFS 61.8 61.3 dB (min)
SNR Signal-to-Noise Ratio fIN = 40.2 kHz, 0.02 dBFS 61.8 61.4 dB (min)
THD Total Harmonic Distortion fIN = 40.2 kHz, 0.02 dBFS 87.4 74.5 dB (max)
SFDR Spurious-Free Dynamic Range fIN = 40.2 kHz, 0.02 dBFS 83.2 76.0 dB (min)
ENOB Effective Number of Bits fIN = 40.2 kHz 9.98 9.89 Bits (min)
ISO Channel-to-Channel Isolation fIN = 20 kHz 78.6 dB
Intermodulation Distortion, Second fa= 19.5 kHz, fb= 20.5 kHz 85.1 dB
Order Terms
IMD Intermodulation Distortion, Third Order fa= 19.5 kHz, fb= 20.5 kHz 81.6 dB
Terms
ANALOG INPUT CHARACTERISTICS
VIN Input Range 0 to VAV
IDCL DC Leakage Current ±1 µA (max)
Track Mode 33 pF
CINA Input Capacitance Hold Mode 3 pF
DIGITAL INPUT CHARACTERISTICS
VA= VD= +2.7V to +3.6V 2.1 V (min)
VIH Input High Voltage VA= VD= +4.75V to +5.25V 2.4 V (min)
VIL Input Low Voltage 0.8 V (max)
IIN Input Current VIN = 0V or VD±0.01 ±1 µA (max)
CIND Digital Input Capacitance 2 4pF (max)
DIGITAL OUTPUT CHARACTERISTICS
VOH Output High Voltage ISOURCE = 200 µA, VD0.5 V (min)
VOL Output Low Voltage ISINK = 200 µA to 1.0 mA, 0.4 V (max)
IOZH, IOZL Hi-Impedance Output Leakage Current ±1 µA (max)
COUT Hi-Impedance Output Capacitance(1) 24pF (max)
Output Coding Straight (Natural) Binary
(1) Data sheet min/max specification limits are ensured by design, test, or statistical analysis.
(2) Tested limits are ensured to AOQL (Average Outgoing Quality Level).
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ADC108S052 Converter Electrical Characteristics(1) (continued)
The following specifications apply for VA= VD= +2.7V to +5.25V, AGND = DGND = 0V, fSCLK = 3.2 MHz to 8 MHz, fSAMPLE =
200 ksps to 500 ksps, and CL= 50pF, unless otherwise noted. Boldface limits apply for TA= TMIN to TMAX: all other limits TA
= 25°C. Limits
Parameter Test Conditions Typ Units
(2)
POWER SUPPLY CHARACTERISTICS (CL= 10 pF)
2.7 V (min)
VA, VDAnalog and Digital Supply Voltages VAVD5.25 V (max)
VA= VD= +2.7V to +3.6V, 0.49 1.1 mA (max)
fSAMPLE = 500 kSPS, fIN = 40 kHz
Total Supply Current
Normal Mode ( CS low) VA= VD= +4.75V to +5.25V, 1.50 2.4 mA (max)
fSAMPLE = 500 kSPS, fIN = 40 kHz
IA+ IDVA= VD= +2.7V to +3.6V, 30 nA
fSCLK = 0 ksps
Total Supply Current
Shutdown Mode (CS high) VA= VD= +4.75V to +5.25V, 60 nA
fSCLK = 0 ksps
VA= VD= +3.0V 1.5 3.3 mW (max)
fSAMPLE = 500 kSPS, fIN = 40 kHz
Power Consumption
Normal Mode ( CS low) VA= VD= +5.0V 7.5 12.1 mW (max)
fSAMPLE = 500 kSPS, fIN = 40 kHz
PCVA= VD= +3.0V 0.09 µW
fSCLK = 0 ksps
Power Consumption
Shutdown Mode (CS high) VA= VD= +5.0V 0.30 µW
fSCLK = 0 ksps
AC ELECTRICAL CHARACTERISTICS
fSCLKMIN Minimum Clock Frequency 0.8 3.2 MHz (min)
fSCLK Maximum Clock Frequency 16 8MHz (max)
50 200 ksps (min)
Sample Rate
fSContinuous Mode 1000 500 ksps (max)
tCONVERT Conversion (Hold) Time 13 SCLK cycles
30 40 % (min)
DC SCLK Duty Cycle 70 60 % (max)
tACQ Acquisition (Track) Time 3SCLK cycles
Throughput Time Acquisition Time + Conversion Time 16 SCLK cycles
tAD Aperture Delay 4 ns
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ADC108S052 Timing Specifications
The following specifications apply for VA= VD= +2.7V to +5.25V, AGND = DGND = 0V, fSCLK = 3.2 MHz to 8 MHz, fSAMPLE =
200 ksps to 500 ksps, and CL= 50pF. Boldface limits apply for TA= TMIN to TMAX: all other limits TA= 25°C.
Limits
Parameter Test Conditions Typ Units
(1)
tCSH CS Hold Time after SCLK Rising Edge 0 10 ns (min)
CS Setup Time prior to SCLK Rising
tCSS 510 ns (min)
Edge
tEN CS Falling Edge to DOUT enabled 5 30 ns (max)
DOUT Access Time after SCLK Falling
tDACC 17 27 ns (max)
Edge
DOUT Hold Time after SCLK Falling
tDHLD 4 ns (typ)
Edge
DIN Setup Time prior to SCLK Rising
tDS 310 ns (min)
Edge
tDH DIN Hold Time after SCLK Rising Edge 3 10 ns (min)
tCH SCLK High Time 0.4 x tSCLK ns (min)
tCL SCLK Low Time 0.4 x tSCLK ns (min)
DOUT falling 2.4 20 ns (max)
CS Rising Edge to DOUT High-
tDIS Impedance DOUT rising 0.9 20 ns (max)
(1) Tested limits are ensured to AOQL (Average Outgoing Quality Level).
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tCSH
SCLK
CS
tCSS
CS
tCONVERT
tACQ tCH
tCL
tEN
tDH
tDS
FOUR ZEROS DB8
DONTC DONTC ADD2 ADD1 ADD0 DONTC DONTC DONTC
DB9 DB7 DB6 B1
14
87654321
DB0
DIN
DOUT
SCLK
CS
tDIS
15 16
tDACC
tDHLD
TWO ZEROS
8 9 10 11 12 13 14 15 16
Track Hold
Power Up
ADD2 ADD1 ADD0
DB9 DB8 DB7 DB6 DB5 DB4 DB3 DB2 DB1 DB0
DIN
DOUT
SCLK
CS
Control register
1 2 3 4 5 6 7
1 2 3 4 5 6 7
ADD2 ADD1 ADD0
8
DB9 DB8 DB7
Power
Down
Power Up
Track Hold
FOUR ZEROS SIX ZEROS
ADC108S052
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Timing Diagrams
Figure 2. ADC108S052 Operational Timing Diagram
Figure 3. ADC108S052 Serial Timing Diagram
Figure 4. SCLK and CS Timing Parameters
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Specification Definitions
ACQUISITION TIME is the time required for the ADC to acquire the input voltage. During this time, the hold
capacitor is charged by the input voltage.
APERTURE DELAY is the time between the fourth falling edge of SCLK and the time when the input signal is
internally acquired or held for conversion.
CONVERSION TIME is the time required, after the input voltage is acquired, for the ADC to convert the input
voltage to a digital word.
CHANNEL-TO-CHANNEL ISOLATION is resistance to coupling of energy from one channel into another
channel.
CROSSTALK is the coupling of energy from one channel into another channel. This is similar to Channel-to-
Channel Isolation, except for the sign of the data.
DIFFERENTIAL NON-LINEARITY (DNL) is the measure of the maximum deviation from the ideal step size of 1
LSB.
DUTY CYCLE is the ratio of the time that a repetitive digital waveform is high to the total time of one period. The
specification here refers to the SCLK.
EFFECTIVE NUMBER OF BITS (ENOB, or EFFECTIVE BITS) is another method of specifying Signal-to-Noise
and Distortion or SINAD. ENOB is defined as (SINAD - 1.76) / 6.02 and says that the converter is equivalent to a
perfect ADC of this (ENOB) number of bits.
FULL POWER BANDWIDTH is a measure of the frequency at which the reconstructed output fundamental
drops 3 dB below its low frequency value for a full scale input.
FULL SCALE ERROR (FSE) is a measure of how far the last code transition is from the ideal LSB below
VREF+and is defined as:
VFSE = Vmax + 1.5 LSB VREF+
where
Vmax is the voltage at which the transition to the maximum code occurs. FSE can be expressed in Volts, LSB
or percent of full scale range. (1)
GAIN ERROR is the deviation of the last code transition (111...110) to (111...111) from the ideal (VREF - 1.5
LSB), after adjusting for offset error.
INTEGRAL NON-LINEARITY (INL) is a measure of the deviation of each individual code from a line drawn from
negative full scale LSB below the first code transition) through positive full scale LSB above the last code
transition). The deviation of any given code from this straight line is measured from the center of that code value.
INTERMODULATION DISTORTION (IMD) is the creation of additional spectral components as a result of two
sinusoidal frequencies being applied to an individual ADC input at the same time. It is defined as the ratio of the
power in both the second or the third order intermodulation products to the power in one of the original
frequencies. Second order products are fa± fb, where faand fbare the two sine wave input frequencies. Third
order products are (2fa± fb) and (fa± 2fb). IMD is usually expressed in dB.
MISSING CODES are those output codes that will never appear at the ADC outputs. The ADC108S052 is
specified not to have any missing codes.
OFFSET ERROR is the deviation of the first code transition (000...000) to (000...001) from the ideal (i.e. GND +
0.5 LSB).
SIGNAL TO NOISE RATIO (SNR) is the ratio, expressed in dB, of the rms value of the input signal to the rms
value of the sum of all other spectral components below one-half the sampling frequency, not including d.c. or
the harmonics included in THD.
SIGNAL TO NOISE PLUS DISTORTION (S/N+D or SINAD) Is the ratio, expressed in dB, of the rms value of the
input signal to the rms value of all of the other spectral components below half the clock frequency, including
harmonics but excluding d.c.
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2
f1
2
f6
2
f2
10 A
A++A
x logTHD = 20
ADC108S052
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SPURIOUS FREE DYNAMIC RANGE (SFDR) is the difference, expressed in dB, between the rms values of the
input signal and the peak spurious signal where a spurious signal is any signal present in the output spectrum
that is not present at the input, including harmonics but excluding d.c.
TOTAL HARMONIC DISTORTION (THD) is the ratio, expressed in dBc, of the rms total of the first five harmonic
components at the output to the rms level of the input signal frequency as seen at the output. THD is calculated
as
where
Af1 is the RMS power of the input frequency at the output and Af2 through Af6 are the RMS power in the first 5
harmonic frequencies. (2)
THROUGHPUT TIME is the minimum time required between the start of two successive conversions. It is the
acquisition time plus the conversion and read out times. In the case of the ADC108S052, this is 16 SCLK
periods.
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Typical Performance Characteristics
TA= +25°C, fSAMPLE = 500 ksps, fSCLK = 8 MHz, fIN = 40.2 kHz unless otherwise stated.
DNL DNL
Figure 5. Figure 6.
INL INL
Figure 7. Figure 8.
DNL vs. Supply INL vs. Supply
Figure 9. Figure 10.
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Typical Performance Characteristics (continued)
TA= +25°C, fSAMPLE = 500 ksps, fSCLK = 8 MHz, fIN = 40.2 kHz unless otherwise stated.
SNR vs. Supply THD vs. Supply
Figure 11. Figure 12.
ENOB vs. Supply DNL vs. VDwith VA= 5.0 V
Figure 13. Figure 14.
INL vs. VDwith VA= 5.0 V DNL vs. SCLK Duty Cycle
Figure 15. Figure 16.
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Typical Performance Characteristics (continued)
TA= +25°C, fSAMPLE = 500 ksps, fSCLK = 8 MHz, fIN = 40.2 kHz unless otherwise stated.
INL vs. SCLK Duty Cycle SNR vs. SCLK Duty Cycle
Figure 17. Figure 18.
THD vs. SCLK Duty Cycle ENOB vs. SCLK Duty Cycle
Figure 19. Figure 20.
DNL vs. SCLK INL vs. SCLK
Figure . Figure 21.
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Typical Performance Characteristics (continued)
TA= +25°C, fSAMPLE = 500 ksps, fSCLK = 8 MHz, fIN = 40.2 kHz unless otherwise stated.
SNR vs. SCLK THD vs. SCLK
Figure . Figure 22.
ENOB vs. SCLK DNL vs. Temperature
Figure 23. Figure 24.
INL vs. Temperature SNR vs. Temperature
Figure 25. Figure 26.
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Typical Performance Characteristics (continued)
TA= +25°C, fSAMPLE = 500 ksps, fSCLK = 8 MHz, fIN = 40.2 kHz unless otherwise stated.
THD vs. Temperature ENOB vs. Temperature
Figure 27. Figure 28.
SNR vs. Input Frequency THD vs. Input Frequency
Figure 29. Figure 30.
ENOB vs. Input Frequency Power Consumption vs. SCLK
Figure 31. Figure 32.
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IN0
MUX
AGND
SAMPLING
CAPACITOR
SW1
-
+CONTROL
LOGIC
CHARGE
REDISTRIBUTION
DAC
SW2
IN7
VA/2
IN0
MUX
AGND
SAMPLING
CAPACITOR
SW1
-
+CONTRO
L
LOGI
C
CHARGE
REDISTRIBUTION
DAC
VA/2
SW2
IN7
ADC108S052
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FUNCTIONAL DESCRIPTION
The ADC108S052 is a successive-approximation analog-to-digital converter designed around a charge-
redistribution digital-to-analog converter.
ADC108S052 OPERATION
Simplified schematics of the ADC108S052 in both track and hold operation are shown in Figure 33 and Figure 34
respectively. In Figure 33, the ADC108S052 is in track mode: switch SW1 connects the sampling capacitor to
one of eight analog input channels through the multiplexer, and SW2 balances the comparator inputs. The
ADC108S052 is in this state for the first three SCLK cycles after CS is brought low.
Figure 34 shows the ADC108S052 in hold mode: switch SW1 connects the sampling capacitor to ground,
maintaining the sampled voltage, and switch SW2 unbalances the comparator. The control logic then instructs
the charge-redistribution DAC to add or subtract fixed amounts of charge to or from the sampling capacitor until
the comparator is balanced. When the comparator is balanced, the digital word supplied to the DAC is the digital
representation of the analog input voltage. The ADC108S052 is in this state for the last thirteen SCLK cycles
after CS is brought low.
Figure 33. ADC108S052 in Track Mode
Figure 34. ADC108S052 in Hold Mode
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SERIAL INTERFACE
An operational timing diagram and a serial interface timing diagram for the ADC108S052 are shown in The
Timing Diagrams section. CS, chip select, initiates conversions and frames the serial data transfers. SCLK (serial
clock) controls both the conversion process and the timing of serial data. DOUT is the serial data output pin,
where a conversion result is sent as a serial data stream, MSB first. Data to be written to the ADC108S052's
Control Register is placed on DIN, the serial data input pin. New data is written to DIN with each conversion.
A serial frame is initiated on the falling edge of CS and ends on the rising edge of CS. Each frame must contain
an integer multiple of 16 rising SCLK edges. The ADC's DOUT pin is in a high impedance state when CS is high
and is active when CS is low. Thus, CS acts as an output enable. Similarly, SCLK is internally gated off when CS
is brought high.
During the first 3 cycles of SCLK, the ADC is in the track mode, acquiring the input voltage. For the next 13
SCLK cycles the conversion is accomplished and the data is clocked out. SCLK falling edges 1 through 4 clock
out leading zeros, falling edges 5 through 14 clock out the conversion result, MSB first, and falling edges 15 and
16 clock out trailing zeros. If there is more than one conversion in a frame (continuous conversion mode), the
ADC will re-enter the track mode on the falling edge of SCLK after the N*16th rising edge of SCLK and re-enter
the hold/convert mode on the N*16+4th falling edge of SCLK. "N" is an integer value.
The ADC108S052 enters track mode under three different conditions. In Figure 2, CS goes low with SCLK high
and the ADC enters track mode on the first falling edge of SCLK. In the second condition, CS goes low with
SCLK low. Under this condition, the ADC automatically enters track mode and the falling edge of CS is seen as
the first falling edge of SCLK. In the third condition, CS and SCLK go low simultaneously and the ADC enters
track mode. While there is no timing restriction with respect to the rising edges of CS and SCLK, see Figure 4 for
setup and hold time requirements for the falling edge of CS with respect to the rising edge of SCLK.
While a conversion is in progress, the address of the next input for conversion is clocked into a control register
through the DIN pin on the first 8 rising edges of SCLK after the fall of CS. See Table 1,Table 2, and Table 3.
There is no need to incorporate a power-up delay or dummy conversion as the ADC108S052 is able to acquire
the input signal to full resolution in the first conversion immediately following power-up. The first conversion result
after power-up will be that of IN0.
Table 1. Control Register Bits
Bit 7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0
DONTC DONTC ADD2 ADD1 ADD0 DONTC DONTC DONTC
Table 2. Control Register Bit Descriptions
Bit #: Symbol: Description
7, 6, 2, 1, 0 DONTC Don't care. The values of these bits do not affect the device.
5 ADD2 These three bits determine which input channel will be sampled and converted at the next
conversion cycle. The mapping between codes and channels is shown in Table 3.
4 ADD1
3 ADD0
Table 3. Input Channel Selection
ADD2 ADD1 ADD0 Input Channel
0 0 0 IN0 (Default)
0 0 1 IN1
0 1 0 IN2
0 1 1 IN3
1 0 0 IN4
1 0 1 IN5
1 1 0 IN6
1 1 1 IN7
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0V +VA - 1.5LSB
0.5LSB ANALOG INPUT
1 LSB = VA / 1024
ADC CODE
111...111
111...110
111...000
011...111
000...010
000...001
000...000
ADC108S052
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SNAS337G SEPTEMBER 2005REVISED MARCH 2013
ADC108S052 TRANSFER FUNCTION
The output format of the ADC108S052 is straight binary. Code transitions occur midway between successive
integer LSB values. The LSB width for the ADC108S052 is VA/ 1024. The ideal transfer characteristic is shown
in Figure 35. The transition from an output code of 00 0000 0000 to a code of 00 0000 0001 is at 1/2 LSB, or a
voltage of VA/ 2048. Other code transitions occur at steps of one LSB.
Figure 35. Ideal Transfer Characteristic
ANALOG INPUTS
An equivalent circuit for one of the ADC108S052's input channels is shown in Figure 36. Diodes D1 and D2
provide ESD protection for the analog inputs. The operating range for the analog inputs is 0 V to VA. Going
beyond this range will cause the ESD diodes to conduct and result in erratic operation.
The capacitor C1 in Figure 36 has a typical value of 3 pF and is mainly the package pin capacitance. Resistor R1
is the on resistance of the multiplexer and track / hold switch and is typically 500 ohms. Capacitor C2 is the
ADC108S052 sampling capacitor, and is typically 30 pF. The ADC108S052 will deliver best performance when
driven by a low-impedance source (less than 100 ohms). This is especially important when using the
ADC108S052 to sample dynamic signals. Also important when sampling dynamic signals is a band-pass or low-
pass filter which reduces harmonics and noise in the input. These filters are often referred to as anti-aliasing
filters.
Figure 36. Equivalent Input Circuit
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Product Folder Links: ADC108S052
IN0
IN7
.
.
.MICROPROCESSOR
DSP
SCLK
CS
DIN
DOUT
AGND
VA
VD
ADC108S052
LP2950 5V
0.1 PF1.0 PF0.1 PF1 PF0.1 PF
DGND
1.0 PF
51:
22:
INPUT
1 nF
ADC108S052
SNAS337G SEPTEMBER 2005REVISED MARCH 2013
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DIGITAL INPUTS AND OUTPUTS
The ADC108S052's digital inputs (SCLK, CS, and DIN) have an operating range of 0 V to VA. They are not prone
to latch-up and may be asserted before the digital supply (VD) without any risk. The digital output (DOUT)
operating range is controlled by VD. The output high voltage is VD- 0.5V (min) while the output low voltage is
0.4V (max).
Applications Information
TYPICAL APPLICATION CIRCUIT
A typical application is shown in Figure 37. The split analog and digital supply pins are both powered in this
example by the LP2950 low-dropout voltage regulator. The analog supply is bypassed with a capacitor network
located close to the ADC108S052. The digital supply is separated from the analog supply by an isolation resistor
and bypassed with additional capacitors. The ADC108S052 uses the analog supply (VA) as its reference voltage,
so it is very important that VAbe kept as clean as possible. Due to the low power requirements of the
ADC108S052, it is also possible to use a precision reference as a power supply.
To minimize the error caused by the changing input capacitance of the ADC108S052, a capacitor is connected
from each input pin to ground. The capacitor, which is much larger than the input capacitance of the
ADC108S052 when in track mode, provides the current to quickly charge the sampling capacitor of the
ADC108S052. An isolation resistor is added to isolate the load capacitance from the input source.
Figure 37. Typical Application Circuit
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uPN +
tN
tN + tS
tS
tN + tSuPS
PC =
ADC108S052
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SNAS337G SEPTEMBER 2005REVISED MARCH 2013
POWER SUPPLY CONSIDERATIONS
There are three major power supply concerns with this product: power supply sequencing, power management,
and the effect of digital supply noise on the analog supply.
Power Supply Sequence
The ADC108S052 is a dual-supply device. The two supply pins share ESD resources, so care must be exercised
to ensure that the power is applied in the correct sequence. To avoid turning on the ESD diodes, the digital
supply (VD) cannot exceed the analog supply (VA) by more than 300 mV, not even on a transient basis.
Therefore, VAmust ramp up before or concurrently with VD.
Power Management
The ADC108S052 is fully powered-up whenever CS is low and fully powered-down whenever CS is high, with
one exception. If operating in continuous conversion mode, the ADC108S052 automatically enters power-down
mode between SCLK's 16th falling edge of a conversion and SCLK's 1st falling edge of the subsequent
conversion (see Figure 2).
In continuous conversion mode, the ADC108S052 can perform multiple conversions back to back. Each
conversion requires 16 SCLK cycles and the ADC108S052 will perform conversions continuously as long as CS
is held low. Continuous mode offers maximum throughput.
In burst mode, the user may trade off throughput for power consumption by performing fewer conversions per
unit time. This means spending more time in power-down mode and less time in normal mode. By utilizing this
technique, the user can achieve very low sample rates while still utilizing an SCLK frequency within the electrical
specifications. The Power Consumption vs. SCLK curve in the Typical Performance Characteristics section
shows the typical power consumption of the ADC108S052. To calculate the power consumption (PC), simply
multiply the fraction of time spent in the normal mode (tN) by the normal mode power consumption (PN), and add
the fraction of time spent in shutdown mode (tS) multiplied by the shutdown mode power consumption (PS) as
shown in Figure 38.
Figure 38. Power Consumption Equation
Power Supply Noise Considerations
The charging of any output load capacitance requires current from the digital supply, VD. The current pulses
required from the supply to charge the output capacitance will cause voltage variations on the digital supply. If
these variations are large enough, they could degrade SNR and SINAD performance of the ADC. Furthermore, if
the analog and digital supplies are tied directly together, the noise on the digital supply will be coupled directly
into the analog supply, causing greater performance degradation than would noise on