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LM2903B-Q1: Output is pulled down when VCC is 0

Daniel Wang (auto)
Intellectual 1990 points
Part Number: LM2903B-Q1

Hi expert,

Hope you are doing well.

For LM2903B-Q1, when VCC is 0, IN+ is in 0-20mV, IN- is 0, the output is in open-drain form, why output would be pulled down? (detected as low)

Thanks.

  • 0
    TI__Guru 53826 points

    Hello Daniel,

    If VCC is 0V, there is no voltage available to turn on the output  transistor  (Vbe > 0.55V). The output starts to function when VCC > 1.3V, but that is still not enough voltage to bias the input stage - so the input stage is still dead. Even if there was some path from the input to the output, 20mV is not enough to turn on the transistor.

    Are you seeing some devices pulling low? Does it work normally when powered?

    I have not ever seen the output pull low with no supply unless it was damaged.