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OPA4322-Q1: OP-AMP Behavior Under Off Condition

Robert Liu1
Prodigy 20 points
Part Number: OPA4322-Q1
Other Parts Discussed in Thread: OPA2348-Q1,

Hello TI Team,

I am using both of the above op amps (OPA4322-Q1 and OPA2348-Q1). When these op-amps are off ( It is possible that (+) input voltage can go up to 16V through a 49.9k resistor.

This leads to the following questions:

1. I wanted to prevent backfeeding when the op-amp is off and reduce overall quiescent current. Note that the voltage divider circuitry is always hot. Therefore I have the MOSFETs and diode to cutoff the current flow when the op-amp is off. The (+) input voltage will go up to 16V however I don't believe this will damage the parts as I have large input impedance (49.9k) to reduce the input current to the OP-AMP. Please confirm.

2. When the OP-AMP is off (V+ and V- are disconnected) will the output voltage go up to VBATT level? Or will it hold to 0V?

Robert Liu

  • 0
    TI__Mastermind 30600 points
    Hi Robert,

    To answer your questions:

    1. 16V through 49.9k should be okay as this is about 300 µA of input current. The datasheet states that the input current must be less than 10mA. For repeated events where input current can flow, we recommend limiting to less than 1mA, which you are doing.

    2. It is possible that you will get an output voltage even with the V+ and V- disconnected, this is due to conduction through internal device structures. Hard to predict exactly what the output voltage will be. Here is a blog that discusses this topic: e2e.ti.com/.../the-self-powering-device

    Thanks,
    Paul