INA849 datasheet(13/28 Pages) TI

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8.3.2 Input Protection

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

rails when there is no gain resistor across the RG pins. For example, a condition of VS– –40 V on one input

and VS+ +40 V on the other input does not cause damage. Internal circuitry on each input provides low series

impedance under normal signal conditions. If the input is overloaded, the protection circuitry limits the input

current to a value of approximately 22 mA, as Figure 8-3 shows.

VIN+ or VIN– Input Voltage (V)

-40

-30

-20

-10

-25

-20

-15

-10

-5

VS =

15 V

VS = 0 V

Figure 8-3. Input Current During an Overvoltage Condition

As shown in Figure 8-4, 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 8-4) 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 8-4. Input Current Path During an Overvoltage Condition

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

RG terminals, the inputs will still be well protected against overvoltage conditions, but precautions must be taken

to ensure the input differential voltage limitations of the INA851 are not exceeded. For example, a condition of

VS+ +40 V on one input and VS+ +40 V on the other input does not cause damage; however, a condition of

VS– –40 V on one input and VS+ +40 V on the other input will cause damage. Precautions may include the use

of external resistors in series with each of the inputs. More detailed guidance is provided in Differential Input

Voltage Limitations.

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INA851

SBOS999 – MARCH 2022

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