AD7785 Analog Devices, AD7785 Datasheet - Page 11

• Manufacturer Part Number: AD7785
• Description: 3-Channel, Low Noise, Low Power, 20-Bit ?-? ADC with On-Chip In-Amp and Reference
• Manufacturer: Analog Devices

Specifications of AD7785

• Resolution (bits): 20bit
• # Chan: 3
• Sample Rate: n/a
• Interface: Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: ± (Vref/Gain)
• Adc Architecture: Sigma-Delta
• Pkg Type: SOP

OUTPUT NOISE AND RESOLUTION SPECIFICATIONS
EXTERNAL REFERENCE
Table 5 shows the output rms noise of the AD7785 for some of
the update rates and gain settings. The numbers given are for
the bipolar input range with an external 2.5 V reference. These
numbers are typical and are generated with a differential input
voltage of 0 V. Table 6 shows the effective resolution, with the
output peak-to-peak (p-p) resolution shown in parentheses. It is
Table 5. Output RMS Noise (μV) vs. Gain and Output Update Rate Using an External 2.5 V Reference
Update Rate (Hz)
4.17
8.33
16.7
33.2
62
123
242
470
Table 6. Typical Resolution (Bits) vs. Gain and Output Update Rate Using an External 2.5 V Reference
Update Rate (Hz)
4.17
8.33
16.7
33.2
62
123
242
470
Gain of 1
0.64
1.04
1.55
2.3
2.95
4.89
11.76
11.33
Gain of 1
20 (20)
20 (19.5)
20 (19)
20 (18.5)
20 (18)
20 (17.5)
18.5 (16)
18.5 (16)
Gain of 2
0.6
0.96
1.45
2.13
2.85
4.74
9.5
9.44
Gain of 2
20 (19.5)
20 (19)
20 (18)
20 (17.5)
19.5 (17)
19 (16.5)
18 (15.5)
18 (15.5)
Gain of 4
0.29
0.38
0.54
0.74
0.92
1.49
4.02
3.07
Gain of 4
20 (19.5)
20 (19)
20 (18.5)
20 (18)
20 (18)
19.5 (17)
18 (15.5)
18.5 (16)
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Gain of 8
Gain of 8
20 (17.5)
0.22
0.26
0.36
0.5
0.58
1
1.96
1.79
20 (19)
20 (18.5)
20 (18)
20 (17.5)
19 (16.5)
18 (15.5)
18.5 (16)
important to note that the effective resolution is calculated
using the rms noise, while the p-p resolution is based on the p-p
noise. The p-p resolution represents the resolution for which
there is no code flicker. These numbers are typical and are
rounded to the nearest LSB.
Gain of 16
Gain of 16
20 (17.5)
0.1
0.13
0.18
0.23
0.29
0.48
0.88
0.99
20 (19)
20 (18.5)
20 (18)
20 (18)
19.5 (17)
18.5 (16)
18 (15.5)
Gain of 32
0.065
0.078
0.11
0.17
0.2
0.32
0.45
0.63
Gain of 32
20 (18.5)
20 (18.5)
20 (18)
20 (17.5)
19.5 (17)
19 (16.5)
18.5 (16)
18 (15.5)
Gain of 64
0.039
0.057
0.087
0.124
0.153
0.265
0.379
0.568
Gain of 64
20 (18.5)
20 (18)
20 (17.5)
19 (16.5)
19 (16.5)
18 (15.5)
17.5 (15)
17 (14.5)
Gain of 128
Gain of 128
0.041
0.055
0.086
0.118
0.144
0.283
0.397
0.593
20 (17.5)
19.5 (17)
19 (16.5)
18.5 (16)
18 (15.5)
17 (14.5)
16.5 (14)
16 (13.5)
AD7785