INA821 datasheet(27/52 Pages) TI

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8.3.4 Input Protection

The inputs of the INA851 device are individually protected for voltages up to ±40 V beyond the power supply

rails. For example, a condition of VS– = –55 V on one input and VS+ = 55 V on the other input does not

cause damage. Internal circuitry on each input provides low series impedance under normal signal conditions.

Figure 8-10 shows that if the input is overloaded, the protection circuitry limits the input current to a value of

approximately 16 mA.

Figure 8-10. Input Current During an Overvoltage Condition

Figure 8-11 shows that during an input overvoltage condition, current flows through the input protection diodes

into the power supplies. If the power supplies are unable to sink current, then place Zener diode clamps (ZD1

and ZD2 in Figure 8-11) on the power supplies to provide a current pathway to ground.

VS+

VS–

Overvoltage

Protection

INx

Input Transistor

VS+

VS–

–

Input Voltage

Source

ZD1

ZD2

RIN

Figure 8-11. Input Current Path During an Overvoltage Condition

If an input stage gain greater than GIN = 1 V/V is implemented, where a gain resistor is present across the

RG pins, the inputs are still well protected against overvoltage conditions; however, make sure that the input

differential voltage limitations of the INA851 are not exceeded. For example, a condition of (VS+) + 40 V on both

inputs does not cause damage. However, a condition of (VS–) – 40 V on one input and (VS+) + 40 V on the other

input can cause damage. Precautions can include the use of external resistors in series with each of the inputs.

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INA851

SBOS999A – MARCH 2022 – REVISED OCTOBER 2022

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