Analog Devices AD7732 Datasheet

2-Channel, ±10 V Input Range, High

FEATURES

High resolution ADC
24 bits no missing codes ±0.0015% nonlinearity
Optimized for fast channel switching
18-bit p-p resolution (21 bits effective) at 500 Hz 16-bit p-p resolution (19 bits effective) at 2 kHz 14-bit p-p resolution (18 bits effective) at 15 kHz On-chip per channel system calibration
2 fully differential analog inputs
Input ranges +5 V, ±5 V, +10 V, ±10 V Overvoltage tolerant Up to ±16.5 V not affecting adjacent channel Up to ±50 V absolute maximum
3-wire serial interface
SPI™, QSPI™, MICROWIRE™, and DSP compatible Schmitt trigger on logic inputs
Single-supply operation
5 V analog supply 3 V or 5 V digital supply
Package: 28-lead TSSOP

APPLICATIONS

PLCs/DCS Multiplexing applications Process control Industrial instrumentation

GENERAL DESCRIPTION

The AD7732 is a high precision, high throughput analog front end. True 16-bit p-p resolution is achievable with a total conversion time of 500 µs (2 kHz channel switching), making it ideally suitable for high resolution multiplexing applications.
The part can be configured via a simple digital interface, which allows users to balance the noise performance against data throughput up to a 15.4 kHz.
The analog front end features two fully differential input channels with unipolar or true bipolar input ranges to ±10 V while operating from a single +5 V analog supply. The part has an overrange and underrange detection capability and accepts an analog input overvoltage to ±16.5 V without degrading the performance of the adjacent channels.
Throughput, 24-Bit ∑-∆ ADC
AD7732

FUNCTIONAL BLOCK DIAGRAM

REFIN(–) REFIN(+)
AIN0(+)
BUFFER
AIN0(–)
MUX
AD7732
AIN1(+)
DD
CALIBRATION
CIRCUITRY
CLOCK
GENERATOR
Figure 1.
AIN1(–)
SYNC/P1
P0
I/O PORT
The differential reference input features “No-Reference” detect capability. The ADC also supports per channel system calibration options. The digital serial interface can be configured for 3-wire operation and is compatible with microcontrollers and digital signal processors. All interface inputs are Schmitt triggered.
The part is specified for operation over the extended industrial temperature range of –40°C to +105°C.
Other parts in the AD7732 family are the AD7734 and the AD7738.
The AD7734 is similar to AD7732, but its analog front end features four single-ended input channels.
The AD7738 analog front end is configurable for four fully differential or eight single-ended input channels, features
0.625 V to 2.5 V bipolar/unipolar input ranges, and accepts a common-mode input voltage from 200 mV to AVDD – 300 mV. The AD7738 multiplexer output is pinned out externally, allowing the user to implement programmable gain or signal conditioning before being applied to the ADC.
REFERENCE
DETECT
24-BIT
Σ−∆ ADC
SERIAL
INTERFACE
CONTROL
LOGIC
DGNDMCLKINMCLKOUTAGND AV
DV
CS
SCLK
DIN
DOUT
RESET
RDY
DD
Rev. 0
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective companies.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781.329.4700 www.analog.com Fax: 781.326.8703 © 2003 Analog Devices, Inc. All rights reserved.
AD7732
TABLE OF CONTENTS
AD7732—Specifications.................................................................. 3
Mode Register............................................................................. 20
Timing Specifications....................................................................... 6
Absolute Maximum Ratings............................................................ 8
Typical Performance Characteristics ............................................. 9
Output Noise and Resolution Specification................................ 10
Chopping Enabled...................................................................... 10
Chopping Disabled..................................................................... 11
Pin Configurations and Functional Descriptions...................... 12
Register Description....................................................................... 14
Register Access............................................................................ 15
Communications Register......................................................... 15
I/O Port Register......................................................................... 16
Revision Register ........................................................................16
Test Register ................................................................................ 16
ADC Status Register................................................................... 17
Checksum Register..................................................................... 17
Digital Interface Description ........................................................ 22
Hardware ..................................................................................... 22
Reset ............................................................................................. 23
Access the AD7732 Registers.................................................... 23
Single Conversion and Reading Data...................................... 23
Dump Mode................................................................................ 24
Continuous Conversion Mode ................................................. 24
Continuous Read (Continuous Conversion) Mode .............. 25
Circuit Description......................................................................... 26
Analog Front End....................................................................... 26
Analog Input’s Extended Voltage Range ................................. 27
Chopping..................................................................................... 27
Multiplexer, Conversion, and Data Output Timing.............. 28
Sigma-Delta ADC....................................................................... 28
Frequency Response .................................................................. 29
ADC Zero-Scale Calibration Register ..................................... 17
ADC Full-Scale Register............................................................ 17
Channel Data Registers ............................................................. 17
Channel Zero-Scale Calibration Registers.............................. 18
Channel Full-Scale Calibration Registers................................ 18
Channel Status Registers ...........................................................18
Channel Setup Registers............................................................ 19
Channel Conversion Time Registers ....................................... 19

REVISION HISTORY

Revision 0: Initial Version
Voltage Reference Inputs........................................................... 29
Reference Detect......................................................................... 29
I/O Port........................................................................................ 30
Calibration................................................................................... 30
ADC Zero-Scale Self-Calibration ............................................ 30
Per Channel System Calibration .............................................. 30
High Common-Mode Voltage Application............................. 31
Outline Dimensions....................................................................... 32
Rev. 0 | Page 2 of 32
AD7732

AD7732—SPECIFICATIONS

Table 1. (–40°C to +105°C; AVDD = 5 V ± 5%; DVDD = 2.7 V to 3.6 V, or 5 V ± 5%; BIAS (all), REFIN(+) = 2.5 V; REFIN(–) = AGND; RA, RB, RC, RD open circuit; AIN Range = ±10 V; f
Parameter Min Typ Max Unit Test Conditions/Comments
ADC PERFORMANCE CHOPPING ENABLED
Conversion Time Rate 372 12190 Hz Configure via Conv. Time Register No Missing Codes
1, 2
24 Bits FW ≥ 6 (Conversion Time ≥ 165 µs)
Output Noise
Resolution
Integral Nonlinearity (INL) Integral Nonlinearity (INL)
1, 2, 3
±0.0003 ±0.0015 % of FSR f
2, 3
±0.0010 ±0.0030 % of FSR f Offset Error (Unipolar, Bipolar)4 ±10 mV Before Calibration Offset Drift vs. Temperature1 ±2.5 µV/°C Gain Error3 ±0.7 % Before Calibration Gain Drift vs. Temperature1 ±3.2 ppm of FS/°C Positive Full-Scale Error4 ±0.7 % of FSR Before Calibration Positive Full-Scale Drift vs. Temp.1 ±3 ppm of FS/°C Bipolar Negative Full-Scale Error5 ±0.0060 % of FSR After Calibration Common-Mode Rejection 50 65 dB At DC Power Supply Sensitivity ±4 ±10 LSB16 At DC, AIN = 7 V, AVDD = 5 V ± 5% Channel-to-Channel Isolation 100 dB At DC, Maximum ±16.5 V AIN Voltage
ADC PERFORMANCE CHOPPING DISABLED
Conversion Time Rate 737 15437 Hz Configure via Conv. Time Register No Missing Codes
1, 2
24 Bits FW ≥ 8 (Conversion Time ≥ 117 µs) Output Noise See Table 7 Resolution
Integral Nonlinearity (INL)
2, 3
±0.0015 % of FSR Offset Error (Unipolar, Bipolar)6 ±10 mV Before Calibration Offset Drift vs. Temperature ±25 µV/°C Gain Error4 ±0.5 % Before Calibration Gain Drift vs. Temperature ±5.3 ppm of FS/°C Positive Full-Scale Error4 ±0.5 % of FSR Before Calibration Positive Full-Scale Drift vs. Temp. ±4 ppm of FS/°C Bipolar Negative Full-Scale Error5 ±0.0060 % of FSR After Calibration Common-Mode Rejection 55 dB At DC Power Supply Sensitivity ±4 LSB16 At DC, AIN = 7 V, AVDD = 5 V ± 5% Channel-to-Channel Isolation 100 dB At DC, Maximum ±16.5 V AIN Voltage
ANALOG INPUTS
Analog Input Differential Voltage7
±10 V Range 0 V to +10 V Range 0 to +10 V
±5 V Range 0 V to +5 V Range 0 to +5 V
AIN Absolute Voltage
1, 2, 8
–16.5 +16.5 V BIAS Voltage1 0 2.5 AVDD V RA, RB, RC, RD Voltage1 –10.5 +20 V AIN Impedance AIN Pin Impedance
1, 9
100 124 kΩ
1, 9
87.5 108.5 kΩ
See
Table 4 See Table 5
and Table 6
See Table 8 and Table 9
±10
±5
V
V
= 6.144 MHz; unless otherwise noted.)
MCLKIN
= 2.5 MHz, VCM = 0 V
MCLKIN
= 6.144 MHz, VCM = 0 V
MCLKIN
Rev. 0 | Page 3 of 32
AD7732
Parameter Min Typ Max Unit Test Conditions/Comments
BIAS Pin Impedance RA, RB, RC, RD Pin Impedance Input Resistor Matching 0.2 %
Input Resistor Temp. Coefficient –30 ppm/°C
REFERENCE INPUTS
REFIN(+) to REFIN(–) Voltage NOREF Trigger Voltage 0.5 V NOREF Bit in Channel Status Register REFIN(+), REFIN(–) Common-Mode Voltage1 0 AVDD V Reference Input DC Current11 400 µA
SYSTEM CALIBRATION
Full-Scale Calibration Limit Zero-Scale Calibration Limit Input Span
LOGIC INPUTS
Input Current Input Current CS
–40 µA
Input Capacitance 5 pF
1
V
1.4 2 V DVDD = 5 V
T+
1
V
0.8 1.4 V DVDD = 5 V
T–
VT+ – V V
1
0.3 0.85 V DVDD = 5 V
T–
1
0.95 2 V DVDD = 3 V
T+
VT– 1 0.4 1.1 V DVDD = 3 V VT+ – V
1
0.3 0.85 V DVDD = 3 V
T–
MCLK IN ONLY
Input Current Input Capacitance 5 pF
V
Input Low Voltage 0.8 V DVDD = 5 V
INL
V
Input High Voltage 3.5 V DVDD = 5 V
INH
V
Input Low Voltage 0.4 V DVDD = 3 V
INL
V
Input High Voltage 2.5 V DVDD = 3 V
INH
LOGIC OUTPUTS13
VOL Output Low Voltage 0.4 V I VOH Output High Voltage 4.0 V I VOL Output Low Voltage 0.4 V I VOH Output High Voltage DVDD – 0.6 V I Floating State Leakage Current
Floating State Leakage Capacitance 3 pF
P0, P1 INPUTS/OUTPUTS Levels Referenced to Analog Supplies
Input Current V
Input Low Voltage 0.8 V AVDD = 5 V
INL
V
Input High Voltage 3.5 V AVDD = 5 V
INH
VOL Output Low Voltage 0.4 V I VOH Output High Voltage 4.0 V I
POWER REQUIREMENTS
AVDD–AGND Voltage 4.75 5.25 V DVDD–DGND Voltage 4.75 5.25 V
2.70 3.60 V AVDD Current (Normal Mode) 13.5 15.9 mA AVDD = 5 V DVDD Current (Normal Mode)14 2.8 3.1 mA DVDD = 5 V
1, 9
12.5 15.5
1, 9
25 31
1, 10
2.475 2.5 2.525 V
1, 12
+1.05 × FS
–1.05 × FS
0.8 × FS
V
2.1 × FS
±1 ±10
±10
±1
±10
k k
V
V
µA µA
µA
µA
µA
CS = DVDD
= DGND, Internal Pull-Up Resistor
CS
= 800 µA, DVDD = 5 V
SINK
= 200 µA, DVDD = 5 V
SOURCE
= 100 µA, DVDD = 3 V
SINK
= 100 µA, DVDD = 3 V
SOURCE
= 7 mA, See Abs. Max. Ratings
SINK
= 200 µA, AVDD = 5 V
SOURCE
Rev. 0 | Page 4 of 32
AD7732
Parameter Min Typ Max Unit Test Conditions/Comments
DVDD Current (Normal Mode) Power Dissipation (Normal Mode) AVDD+DVDD Current (Standby Mode)15 140 µA Power Dissipation (Standby Mode)15 750 µW
14
1.0 1.5 mA DVDD = 3 V
14
85 100 mW
1
Specifications are not production tested but guaranteed by design and/or characterization data at initial product release.
2
See Typical Performance Characteristics.
3
VCM = Common-Mode Voltage = 0 V.
4
Specifications before calibration. Channel system calibration reduces these errors to the order of the noise.
5
Applies after the zero-scale and full-scale calibration. The negative full-scale error represents the remaining error after removing the offset and gain error.
6
ADC zero-scale self-calibration reduces this error to ±10 mV. Channel zero-scale system calibration reduces this error to the order of the noise.
7
For specified performance. The output data span corresponds to the specified nominal input voltage range. The ADC is functional outside the nominal input voltage range, but the performance might degrade. Outside the nominal input voltage range, the OVR bit in the channel status register is set and the channel data register value depends on the CLAMP bit in the mode register. See the register and circuit descriptions for more details.
8
The AIN absolute voltage of ±16.5 V applies for a nominal VBIAS voltage of +2.5 V. By configuring the BIAS and RA to RD pins differently, the part will work with higher AIN absolute voltages as long as the internal voltage seen by the multiplexer and the input buffer is within 200 mV to AV BIAS, and RA to RD pins must never exceed the values specified in the Absolute Maximum Ratings.
9
Pin impedance is from the pin to the internal node. In normal circuit configuration, the analog input total impedance is typically 108.5 kΩ + 15.5 kΩ = 124 kΩ.
10
For specified performance. Part is functional with lower V
11
Dynamic current charging the sigma-delta modulator input switching capacitor.
12
Outside the specified calibration range, calibration is possible but the performance may degrade.
13
These logic output levels apply to the MCLK OUT output when it is loaded with a single CMOS load.
14
With external MCLK, MCLKOUT is disabled (the CLKDIS bit is set in the mode register).
15
External MCLKIN = 0 V or DVDD, Digital Inputs = 0 V or DVDD, and P0 and P1 = 0 V or AV
.
REF
DD.
– 300 mV. Absolute voltage for the AIN,
DD
Rev. 0 | Page 5 of 32
AD7732

TIMING SPECIFICATIONS

Table 2. (AVDD = 5 V ± 5%; DVDD = 2.7 V to 3.6 V, or 5 V ± 5%; Input Logic 0 = 0 V; Logic 1 = DVDD; unless otherwise noted.)
Parameter Min Typ Max Unit Test Conditions/Comments
Master Clock Range 1 6.144 MHz t1 50 ns
t2 500 ns
Read Operation t4 0 ns t 0 60 ns DVDD of 4.75 V to 5.25 V 0 80 ns DVDD of 2.7 V to 3.3 V t 0 60 ns DVDD of 4.75 V to 5.25 V 0 80 ns DVDD of 2.7 V to 3.3 V t6 50 ns SCLK High Pulsewidth t7 50 ns SCLK Low Pulsewidth t8 0 ns t Write Operation t11 0 ns t12 30 ns Data Valid to SCLK Rising Edge Setup Time t13 25 ns Data Valid after SCLK Rising Edge Hold Time t14 50 ns SCLK High Pulsewidth t15 50 ns SCLK Low Pulsewidth t16 0 ns
1
Pulsewidth
SYNC
Pulsewidth
RESET
Falling Edge to SCLK Falling Edge Setup Time
CS
2
SCLK Falling Edge to Data Valid Delay
5
2, 3
5A
4
10 80 ns Bus Relinquish Time after SCLK Rising Edge
9
Falling Edge to Data Valid Delay
CS
Rising Edge after SCLK Rising Edge Hold Time
CS
Falling Edge to SCLK Falling Edge Setup
CS
Rising Edge after SCLK Rising Edge Hold Time
CS
1
Sample tested during initial release to ensure compliance. All input signals are specified with tr = tf = 5 ns (10% to 90% of DVDD) and timed from a voltage level of
1.6 V. See and . Figure 2 Figure 3
2
These numbers are measured with the load circuit of and defined as the time required for the output to cross the VOL or VOH limits.
3
This specification is relevant only if CS goes low while SCLK is low.
4
These numbers are derived from the measured time taken by the data output to change 0.5 V when loaded with the circuit of . The measured number is then
extrapolated back to remove effects of charging or discharging the 50 pF capacitor. This means that the times quoted in the Timing Characteristics are the true bus relinquish times of the part and as such are independent of external bus loading capacitances.
Figure 4
Figure 4
Rev. 0 | Page 6 of 32
AD7732
SCLK
T
CS
t
4
SCLK
t
5
t
5A
DOUT MSB LSB
t
6
t
7
Figure 2. Read Cycle Timing Diagram
CS
t
DIN
11
t
12
MSB
t
14
t
15
t
13
Figure 3. Write Cycle Timing Diagram
LSB
t
8
t
9
t
16
(800µA AT DVDD = 5V
I
SINK
O OUTPUT
PIN
50pF
100µA AT DV
I
(200µA AT DVDD = 5V
SOURCE
100µA AT DV
1.6V
DD
= 3V)
DD
= 3V)
Figure 4. Load Circuit for Access Time and Bus Relinquish Time
Rev. 0 | Page 7 of 32
AD7732

ABSOLUTE MAXIMUM RATINGS

Table 3. TA = 25°C, unless otherwise noted.
Parameter Rating
AVDD to AGND, DVDD to DGND –0.3 V to +7 V AGND to DGND –0.3 V to +0.3 V AVDD to DVDD –5 V to +5 V AIN to AGND –50 V to +50 V RA, RB, RC, RD to AGND –11 V to +25 V BIAS to AGND –0.3 V to AVDD + 0.3 V REFIN+, REFIN– to AGND –0.3 V to AVDD + 0.3 V P0, P1 Voltage to AGND –0.3 V to AVDD + 0.3 V P0, P1 Current (T P0, P1 Current (T P0, P1 Current (T Digital Input Voltage to DGND –0.3 V to DVDD + 0.3 V Digital Output Voltage to DGND –0.3 V to DVDD + 0.3 V Operating Temperature Range –40°C to +105°C Storage Temperature Range –65°C to +150°C Junction Temperature 150°C TSSOP Package, Power Dissipation 660 mW
θJA Thermal Impedance
Lead Temperature, Soldering
Vapor Phase (60 sec) 215°C Infrared (15 sec) 220°C
= 70°C) 8 mA
MAX
= 85°C) 5 mA
MAX
= 105°C) 2.5 mA
MAX
97.9°C/W
Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device. This is a stress rating only; functional operation of the device at these or any other conditions above those indicated in the operational section of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
Rev. 0 | Page 8 of 32
AD7732

TYPICAL PERFORMANCE CHARACTERISTICS

25
24
CHOP = 1
23
22
21
20
19
NO MISSING CODES
18
17
16
12345678910
FILTER WORD
Figure 5. No Missing Codes Performance, Chopping Enabled
25
24
CHOP = 0
23
22
21
20
19
NO MISSING CODES
18
17
16
12345678910
FILTER WORD
Figure 6. No Missing Codes Performance, Chopping Disabled
15
VCM = 0V
60
MCLK = 6.144MHz
= 0V
V
50
40
30
INL – ppm
20
10
CM
0
20–15–10–50 5101520
AIN DIFFERENTIAL VOLTAGE – V
Figure 8. Typical INL vs. AIN Differential Voltage, AIN Common-Mode
Voltage = 0 V, MCLK = 6.144 MHz, BIAS(+) = BIAS(–) = 2.5 V
60
50
40
30
INL – ppm
20
10
0
–15 –10 –5 0 5 10 15
AIN COMMON-MODE VOLTAGE – V
MCLK = 6.144MHz
Figure 9. Typical INL vs. AIN Common-Mode Voltage, ±10 V Differential
Signal, MCLK = 6.144 MHz, BIAS(+) = BIAS(–) = 2.5 V
20
10
INL – ppm
5
0
01234567
MCLK FREQUENCY – MHz
Figure 7. Typical INL vs. MCLK Frequency, ±10 V Differential Signal, AIN
Common-Mode Voltage = 0 V, BIAS(+) = BIAS(–) = 2.5 V
Rev. 0 | Page 9 of 32
15
10
CURRENT – mA
DD
+ DV
DD
5
AV
0
01234567
MCLK FREQUENCY – MHz
Figure 10. Typical Supply Current vs. MCLK Frequency,
Normal Operation, Converting
AD7732

OUTPUT NOISE AND RESOLUTION SPECIFICATION

The AD7732 can be operated with chopping enabled or disabled, allowing the ADC to be programmed to either optimize the throughput rate and channel switching time or to optimize the offset drift performance. Noise tables for these two primary modes of operation are outlined below for a selection of output rates and settling times.
The AD7732 noise performance depends on the selected chopping mode, the filter word (FW) value, and the selected analog input range. The AD7732 noise will not vary significantly with MCLK frequency.

Chopping Enabled

The first mode, in which the AD7732 is configured with chopping enabled (CHOP = 1), provides very low noise with
Table 4. Typical Output RMS Noise in µV vs. Conversion Time and Input Range with Chopping Enabled
FW Conversion Time
Register
127 FFh 2686 372 200 9.6
46 AEh 999 1001 520 15.5 22 96h 499 2005 1040 22.7 17 91h 395 2534 1300 26.1
8 88h 207 4826 2500 39.2 6 86h 166 6041 3100 46.0 2 82h 82 12166 6300 120.0
Conversion Time
(µs)
Output Data Rate
(Hz)
lower output rates. Table 4 to Table 6 show the –3 dB frequencies and typical performance versus the channel conversion time and equivalent output data rate, respectively. shows the typical output rms noise. Table 5 shows the typical effective resolution based on rms noise. Table 6 shows the typical output peak-to-peak resolution, representing values for which there will be no code flicker within a 6-sigma limit. The peak-to-peak resolutions are not calculated based on rms noise but on peak-to-peak noise.
These typical numbers are generated from 4096 data samples acquired in continuous conversion mode with an analog input voltage set to 0 V and MCLK = 6.144 MHz. The conversion time is selected via the channel conversion time register.
–3 dB Frequency
(Hz)
RMS Noise
(µV)
Table 5. Typical Effective Resolution in Bits vs. Conversion Time and Input Range with Chopping Enabled
Conversion Time
Register
127 FFh 2686 372 200 21.0 20.0 20.0 19.0
46 AEh 999 1001 520 20.3 19.3 19.3 18.3
22 96h 499 2005 1040 19.7 18.7 18.7 17.7
17 91h 395 2534 1300 19.5 18.5 18.5 17.5
8 88h 207 4826 2500 19.0 18.0 18.0 17.0
6 86h 166 6041 3100 18.7 17.7 17.7 16.7
2 82h 82 12166 6300 17.3 16.3 16.3 15.3
(µs)
Output Data Rate
(Hz)
–3 dB Frequency
(Hz)
Input Range/Effective Resolution (Bits) FW Conversion Time
±10 V 0 V to +10 V ±5 V 0 V to +5 V
Table 6. Typical Peak-to-Peak Resolution in Bits vs. Conversion Time and Input Range with Chopping Enabled
Conversion Time
Register
127 FFh 2686 372 200 18.1 17.1 17.1 16.1
46 AEh 999 1001 520 17.4 16.4 16.4 15.4 22 96h 499 2005 1040 16.9 15.9 15.9 14.9 17 91h 395 2534 1300 16.7 15.7 15.7 14.7
8 88h 207 4826 2500 16.2 15.2 15.2 14.2 6 86h 166 6041 3100 15.8 14.8 14.8 13.8 2 82h 82 12166 6300 15.0 13.4 13.4 12.4
(µs)
Output Data Rate
(Hz)
–3 dB Frequency
(Hz)
Input Range/Peak-to-Peak Resolution (Bits) FW Conversion Time
±10 V 0 V to +10 V ±5 V 0 V to +5 V
Rev. 0 | Page 10 of 32
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