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LM2904B-Q1: input offset current and input bias current

Frank QIN
Expert 6405 points
Part Number: LM2904B-Q1

Tool/software:

Hi Team,

We have two questions based on LM2904B-Q1 this kind of op amp.

1. How should we consider the  'input offset current' and 'input bias current'? Are these two current low means better? I suppose offset current should be low but bias current can be a mid range?

2. Do we have any power up sequency restrictions on this LM2904B-Q1? If we apply 50mV at IN+ first, then apply 13V at VS after 300ms, would that be a risk?

Thanks!

Best,

Frank

  • 0
    Guru 264040 points

    1. Lower is better.

    2. This device has overvoltage-tolerant inputs; see the absolute maximum ratings.

  • 0 in reply to Clemens Ladisch
    TI__Mastermind 22670 points

    Hi Frank,

    Clemens is right on both. 

    1. Lower is better. Both input offset current and input bias current can lead to an increase in an error on your output voltage. Check out the Vos and Ib - Specifications video for more details on how this will cause error on the output. I took a snippet of one of the slides that shows the calculations. 

    2. To add to Clemens comment, if you are going to be turning on the inputs before the supply voltage, I highly recommend finding a way to ensure that you limit the current from the input signal that could be used to turn on the ESD diode structure and potentially damaging the device. If 50mV is as much as you expect the input signal to reach, that is likely too low of a voltage for the ESD diodes to turn on. 

    Best Regards,

    Robert Clifton