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LM2903-Q1: negative power supply problem

Mingkang Song
Intellectual 1110 points
Part Number: LM2903-Q1
Other Parts Discussed in Thread: LM339

The comparator is powered by dual power supplies, and after a problem with the negative power supply, the comparator output is abnormal, can you help explain how the negative voltage power supply affects the three ports of the comparator (IN+, IN-, OUT)?

  • 0
    Guru 276960 points

    As long as you do not exceed the absolute maximum ratings, the output will recover quickly. But if the negative supply goes above the inputs, then there is no guarantee. (In that case, an external clamping diode might help.)

    Are you using hysteresis? (Please show the schematic.)

  • 0
    TI__Guru 53316 points

    Hello Mingkang,

    There are parasitic transistors in parallel with the input devices that are normally reverse biased. Pulling the inputs below ground turns on these parasitic transistors and currents start flowing where they should not - even between different channels. This is a drawback of a junction isolated process. As Clemens said, as long as the currents are kept below Abs Max, there should not be damage, but proper operation is not warranted under those conditions.

    Please see section 3.8 of the LM339 family application note:

     Application Design Guidelines for LM339, LM393, TL331 Family Comparators