transistors. The matched PNP transistors, Q1 and Q2, shift the input voltages of both inputs up by a diode drop,

and (through the feedback network) shift the output of A1 and A2 by approximately 0.6 V. The output of A1 and

A2 is well within the linear range when the inputs are within the single supply ground. When inputs are within the

supply ground, differential measurements can be made at the ground level. As a result of this input level-shifting,

the voltages at pin 1 and pin 8 are not equal to the respective input pin voltages. For most applications, this

inequality is not important because only the gain-setting resistor connects to these pins.

8.3.3 Input Protection

The inputs of the INA823 device are individually protected for voltages up to ±60 V and for short transients up

to ±80 V. For example, a condition of –60 V on one input and +60 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 4 mA.

Overvoltage

Protection

IN

Input Transistor

+V

-V

+

–

Input Voltage

Source

ZD1

ZD2

Figure 8-6. Input Current Path During an Overvoltage Condition

During an input overvoltage condition, current flows through the input protection diodes into the power supplies,

as shown in Figure 8-6. If the power supplies are unable to sink current, then Zener diode clamps (ZD1 and ZD2

in Figure 8-6) must be placed on the power supplies to provide a current pathway to ground. Figure 8-7 shows

the input current for input voltages from –80 V to +80 V when the INA823 is powered by ±15-V supplies.

Figure 8-7. Input Current vs Input Overvoltage

8.4 Device Functional Modes

The INA823 has a single functional mode and is operational when the power supply voltage is greater than 2.7 V

(±1.35 V). The maximum power-supply voltage for the INA823 is 36 V (±18 V).

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INA823

SBOSA75A – JULY 2021 – REVISED JULY 2021

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Product Folder Links: INA823