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LM8261: Absolute maximum signal input pin current not defined

Albin Kasper
Prodigy 10 points
Part Number: LM8261

Many op amps define an absolute maximum signal input pin current. The LM8261 doesn't seem to have this spec defined in the datasheet. I'd like to know what it is, so I can protect the device inputs from being driven, when the device isn't powered. 

  • 0
    TI__Mastermind 24641 points

    Hey Albin,

    Since there is not a characterized limit, there are just design rules of thumb. Modern Op Amps have input current limits of 10mA, with 1mA for sustained conditions. The safest way to protect the input would be with external diodes before a series resistor (example below, values are placeholders).

    These diodes will steer current to the supply rails before they can damage the amplifier. The forward voltage should be selected to be less than 0.8V, or you may add the resistor (R3 in the schematic) of sufficient resistance value to ensure the input voltage remains below 0.8V.

    Best,
    Jerry

  • 0 in reply to Jerry Madalvanos
    Prodigy 10 points

    I appreciate this input, but I'd like to get a firm number on the current. Although I agree with the currents mentioned in general, I've received specs as low as 1mA for absolute maximum. Using the suggested approach and a firm spec, I can have better confidence in the resistor value.

  • 0 in reply to Albin Kasper
    TI__Mastermind 24641 points

    Hey Albin,

    Unfortunately we don't have data on what a firm input current limit would be. This would have to be characterized with a statistically significant number of devices. Even if we tested this on a bench in lab and see it "function" up to a certain current, we could have impacts that are detrimental to the long-term use of the device, even if the immediate performance is not impacted.

    Using the above method with the external protection diodes is the most robust solution to protect from electrical overstress.

    Best,
    Jerry

  • 0 in reply to Jerry Madalvanos
    Prodigy 10 points

    Jerry,

    OK. I appreciate your input and will use best practices mentioned. Thank you!

    Albin