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.
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
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
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
kΩ
kΩ
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 2Figure 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
DOUTMSBLSB
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
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
–15–10–5051015
AIN COMMON-MODE VOLTAGE – V
MCLK = 6.144MHz
Figure 9. Typical INL vs. AIN Common-Mode Voltage, ±10 V Differential
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
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