AD622 Analog Devices, AD622 Datasheet - Page 8

• Manufacturer Part Number: AD622
• Description: Low Cost Instrumentation Amplifier
• Manufacturer: Analog Devices

AD622
Error Source
ABSOLUTE ACCURACY at T
DRIFT TO +85 C
RESOLUTION
GAIN SELECTION
The AD622’s gain is resistor programmed by R
cisely, by whatever impedance appears between Pins 1 and 8.
The AD622 is designed to offer gains as close as possible to
popular integer values using standard 1% resistors. Table II
shows required values of R
G = 1, the R
gain R
To minimize gain error avoid high parasitic resistance in series
with R
TC—less than 10 ppm/ C for the best performance.
Total RTI Offset Voltage, V
Input Offset Current, nA
CMR, dB
Gain Drift, ppm/ C
Total RTI Offset Voltage, V/ C
Input Offset Current, pA/ C
Gain Nonlinearity, ppm of Full Scale
Typ 0.1 Hz–10 Hz Voltage Noise, V p-p
G
G
, and to minimize gain drift, R
can be calculated by using the formula
G
pins are unconnected (R
R
G
G
A
for various gains. Note that for
= +25 C
50.5 k
G 1
G
G
AD622 Circuit
Calculation
250 V + 1500 V/10
2.5 nA 1 k
86 dB 50 ppm 0.5 V
(50 ppm + 5 ppm) 60 C
(2 V/ C 15 V/ C/10) 60 C 9 V/ C 2 60 C
2 pA/ C 1 k
10 ppm
0.6 V p-p
= ). For any arbitrary
should have a low
G
Table I. Make vs. Buy Error Budget
, or more pre-
60 C
–8–
“Homebrew” Circuit
Calculation
800 V 2
15 nA 1 k
(0.1% Match 0.5 V)/10 V
Total Absolute Error
(50 ppm)/ C 60 C
155 pA/ C 1 k
Total Drift Error
20 ppm
0.55 V p-p
Total Resolution Error
Grand Total Error
Desired
Gain
2
5
10
20
33
40
50
65
100
200
500
1000
Table II. Required Values of Gain Resistors
2
60 C
1% Std Table
Value of R
51.1 k
12.7 k
5.62 k
2.67 k
1.58 k
1.3 k
1.02 k
787
511
255
102
51.1
Total Error
in ppm
Relative to 1 V FS
AD622
G
,
3510.12
427.5
3300
3948
0.12
10.6
400
210
2.5
0.6
25
10
Calculated
Gain
1.988
4.976
9.986
19.91
32.96
39.85
50.50
65.17
99.83
199.0
496.1
989.3
Total Error
in ppm
Relative to 1 V FS
Homebrew
REV. C
4089.3
20.778
0.778
1600
1665
3000
1080
5575
9.3
15
50
20