INA821 datasheet(18/36 Pages) TI

18 / 36 page

8.3.2 Gain Drift

The stability and temperature drift of external gain setting resistor RG also affects gain. The contribution of RG to

gain accuracy and drift is determined from Equation 1.

The best gain drift of 5 ppm/

℃ (maximum) is achieved when the INA849 uses G = 1 without RG connected. In

this case, gain drift is limited by the mismatch of the temperature coefficient of the integrated 5-kΩ resistors in

differential amplifier A3. At gains greater than 1, gain drift increases as a result of the individual drift of the 3-kΩ

resistors in the feedback of A1 and A2, relative to the drift of external gain resistor RG.

The low temperature coefficient of the internal feedback resistors improves the overall temperature stability of

applications using gains greater than 1 V/V over alternate solutions.

The low resistor values required for high gain make wiring resistance an important consideration. Sockets add to

the wiring resistance and contribute additional gain error (such as a possible unstable gain error) at gains of

approximately 100 or greater.

To maintain stability, avoid parasitic capacitance of more than a few picofarads at RG connections. Careful

matching of any parasitics on the RG pins maintains optimal CMRR over frequency.

8.3.3 Wide Input Common-Mode Range

The linear input voltage range of the INA849 input circuitry extends within 2.5 V (maximum) of both power

supplies, and maintains excellent common-mode rejection throughout this range. The common-mode range for

the most common operating conditions are shown in Figure 8-2 and Figure 8-3. The common-mode range for

other operating conditions is best calculated using the Common-Mode Input Range Calculator for

Instrumentation Amplifiers.

VS = ±5 V, ±12 V, ±18 V

G = 1

Figure 8-2. Input Common-Mode Voltage vs Output

Voltage

VS = ±5 V, ±12 V, ±18 V

G = 100

Figure 8-3. Input Common-Mode Voltage vs Output

Voltage

8.4 Device Functional Modes

The INA849 has a single functional mode and is operational when the power-supply voltage is greater than 8 V

(±4 V). The maximum power-supply voltage for the INA849 is 36 V (±18 V).

INA849

SBOS945A – NOVEMBER 2020 – REVISED DECEMBER 2020

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