Datasheet

AD7747
Rev. 0 | Page 3 of 28
SPECIFICATIONS
V
DD
= 2.7 V to 3.6 V or 4.75 V to 5.25 V; GND = 0 V; EXC = ±V
DD
× 3/8; −40°C to +125°C, unless otherwise noted.
Table 1.
Parameter Min Typ Max Unit Test Conditions/Comments
CAPACITIVE INPUT
Conversion Input Range ±8.192 pF
1
Factory calibrated
Integral Nonlinearity (INL)
2
±0.01 % of FSR
1
No Missing Codes
2
24 Bit Conversion time ≥ 124 ms
Resolution, p-p 16.5 Bit Conversion time 124 ms, see Table 5
Resolution Effective 19.1 Bit Conversion time 124 ms, see Table 5
Output Noise, rms 11.0
aF/√Hz
Conversion time 124 ms, see Table 5
Absolute Error
3
±10 fF
1
25°C, V
DD
= 5 V, after offset calibration
Offset Error
4, 5
32 aF
1
After system offset calibration,
excluding effect of noise
4
System Offset Calibration Range
5
±1 pF
Offset Deviation over Temperature
2
0.4 fF See Figure 6
Gain Error
6
0.02 0.11 % of FS
1
25°C, V
DD
= 5 V
Gain Drift vs. Temperature
2
−23 −26 −29 ppm of FS/°C
Power Supply Rejection
2
0.5 4 fF/V
Normal Mode Rejection
5
72 dB 50 Hz ± 1%, conversion time 124 ms
60 dB 60 Hz ± 1%, conversion time 124 ms
CAPDAC
Full Range 17 21 pF 6-bit CAPDAC
Differential Nonlinearity (DNL) 0.3 LSB See Figure 16
Drift vs. Temperature
2
26 ppm of FS/°C
EXCITATION
Frequency 16 kHz
AC Voltage Across Capacitance ±V
DD
× 3/8 V To be configured via digital interface
Average DC Voltage Across Capacitance V
DD
/2 V
TEMPERATURE SENSOR
7
V
REF
internal
Resolution 0.1 °C
Error
2
±0.5 ±2 °C Internal temperature sensor
±2 °C External sensing diode
8
VOLTAGE INPUT
7
V
REF
internal or V
REF
= 2.5 V
Differential VIN Voltage Range ±V
REF
V
Absolute VIN Voltage
2
GND − 0.03 V
DD
+ 0.03 V
Integral Nonlinearity (INL) ±3 ±15 ppm of FS
No Missing Codes
2
24 Bit Conversion time = 122.1 ms
Resolution, p-p 16 Bits
Conversion time = 62 ms,
see Table 6 and Table 7
Output Noise 3 μV rms
Conversion time = 62 ms,
see Table 6 and Table 7
Offset Error ±3 μV
Offset Drift vs. Temperature 15 nV/°C
Full-Scale Error
2, 9
0.025 0.1 % of FS
Full-Scale Drift vs. Temperature 5 ppm of FS/°C Internal reference
0.5 ppm of FS/°C External reference
Average VIN Input Current 300 nA/V
Analog VIN Input Current Drift ±50 pA/V/°C
Power Supply Rejection 80 dB Internal reference, V
IN
= V
REF
/2
90 dB External reference, V
IN
= V
REF
/2