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INA149: Input Voltage Protection

Part Number: INA149


The Difference amplifier INA149 in our circuit gets Input common mode voltage of 30V. During one particular testing, we found that the IC got damaged and we are trying to debug the issue. We are wondering about ESD protection diodes in the IC. Suppose the Input Voltage is up before the Power supply (+/-15V), will this cause damage to the IC. Page-13 of datasheet mentions that the current through ESD diode must be limited to 10mA. We have a 100 ohm resistor at the input pin. So when the input pin voltage reaches 30V & if the Power supply pin does not have any Voltage, Will the IC be damaged? The current through ESD diode will be 30mA in this case.



  • Hi Veerasamy,

    If the power supply is disconnected/in a high impedance state with an input voltage present, then the part will attempt to power up through the input ESD cells that clamp to the rails. However, the ESD cells reside on the internal amplifier inputs, not the package inputs. So you have approximately 380kOhms of resistance between the input signal and the ESD structure, meaning that the current through the ESD structure will actually be less than 100uA. This should not damage the device at all.

    If you can share some more information about your system and the conditions when you observed the failure we should be able to help you identify the cause of the failure.


    Zak Kaye
    Precision Amplifiers Applications