AD622ARZ-R7 データシートの表示（PDF） - Analog Devices

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AD622ARZ-R7

Low Cost Instrumentation Amplifier

Analog Devices 

Data Sheet

GAIN SELECTION

The AD622 gain is resistor programmed by RG or, more

precisely, by whatever impedance appears between Pin 1 and

Pin 8. The AD622 is designed to offer gains as close as possible

to popular integer values using standard 1% resistors. Table 6

shows required values of RG for various gains. Note that for

G = 1, the RG pins are unconnected (RG = ∞). For any arbitrary

gain, RG can be calculated by using the formula

50.5 k Ω

RG = G −1

To minimize gain error, avoid high parasitic resistance in series

with RG. To minimize gain drift, RG should have a low temperature

coefficient less than 10 ppm/°C for the best performance.

Table 6. Required Values of Gain Resistors

Desired

Gain

1% Std Table Value of RG, Ω

2

51.1 k

5

12.7 k

10

5.62 k

20

2.67 k

33

1.58 k

40

1.3 k

50

1.02 k

65

787

100

511

200

255

500

102

1000

51.1

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

INPUT AND OUTPUT OFFSET VOLTAGE

The low errors of the AD622 are attributable to two sources:

input and output errors. The output error is divided by G when

referred to the input. In practice, the input errors dominate at

high gains and the output errors dominate at low gains. The

total VOS for a given gain is calculated as follows:

Total Error RTI = input error + (output error/G)

Total Error RTO = (input error × G) + output error

AD622

REFERENCE TERMINAL

The reference terminal potential defines the zero output voltage

and is especially useful when the load does not share a precise

ground with the rest of the system. The reference terminal provides

a direct means of injecting a precise offset to the output, with an

allowable range of 2 V within the supply voltages. Parasitic

resistance should be kept to a minimum for optimum CMR.

INPUT PROTECTION

The AD622 safely withstands an input current of ±60 mA for

several hours at room temperature. This is true for all gains and

power on and off, which is useful if the signal source and amplifier

are powered separately. For longer time periods, the input

current should not exceed 6 mA.

For input voltages beyond the supplies, a protection resistor should

be placed in series with each input to limit the current to 6 mA.

These can be the same resistors as those used in the RFI filter.

High values of resistance can impact the noise and AC CMRR

performance of the system. Low leakage diodes (such as the

BAV199) can be placed at the inputs to reduce the required

protection resistance.

+SUPPLY

R

+IN

AD622

VOUT

R

REF

–IN

–SUPPLY

Figure 18. Diode Protection for Voltages Beyond Supply

Rev. E | Page 11 of 16

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