8.3.2 Input Protection

The inputs of PGA855 are individually protected for voltages up to ±40 V beyond either supply. For example, an

input common-mode voltage anywhere between –55 V and +55 V does not cause damage when powered from

±15-V supplies. Internal circuitry on each input provides low series impedance under normal signal conditions,

thus maintaining high performance under normal operating conditions. If the input is overloaded, the protection

circuitry limits the input current to a value of approximately 4.8 mA. Figure 8-2 shows the input protection

functionality during an overvoltage condition.

Figure 8-2. Input Current vs Input Overvoltage

Figure 8-3 shows that during an input overvoltage condition, current flows through the input protection diodes

into the power supplies. In applications where the power supplies are unable to sink current, place Zener diode

clamps (ZD1 and ZD2) 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 8-3. Input Current Path During an Overvoltage Condition

PGA855

SBOSAE0 – APRIL 2023

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