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LM2903B-Q1: Lm2903b-q1

bellapu sai srinivas
Prodigy 20 points
Part Number: LM2903B-Q1
Other Parts Discussed in Thread: LM2903B, PSPICE-FOR-TI, TINA-TI

Tool/software:

Why is the LM2903B comparator IC operating with an 8V supply voltage but not a 22V supply? It functions correctly with 24V, but not 22V; this is unexpected. Assistance with troubleshooting this issue is requested.

  • 0
    TI__Expert 6420 points

    Hi Bellapu,

    I can help you troubleshoot this issue.

    Could you please provide a schematic of how you are using the LM2903B so that I can have a better idea of what the issue is?

    In addition, you mention three different supplies here: 8V, 22V, and 24V. Just to confirm, the device works at 8V and 24V, but not at 22V.

    Usually, improper outputs at different supplies is caused by input common mode voltage range violations. If both inputs are outside of the input common mode voltage range, the output may be incorrect. Could you please provide the input and output voltages for your testing at each of these supplies?

    Thanks,

    Ho

  • 0
    Prodigy 20 points

    hello HO SIU,

    Good morning!

    This is the whole circuit we are using,actually while iam providing lm2903b with 8V and 24v supply ,the circuit is working fine.but with 22v the output of opamp  is behaving strange.Could you please help me with it?

  • 0 in reply to bellapu sai srinivas
    TI__Expert 6420 points

    Hi Bellapu,

    Let me preface this by saying that it appears that you are using LTSpice for simulation. I cannot help troubleshoot using a competitor's simulation software; our models are meant to be simulated using TINA-TI or PSpice-for-TI.

    Just to clarify, LM2903B is an open-drain output comparator, not an op amp. The LM2903B is not meant to be operated in negative feedback and it has an open-drain output. This means that there is no internal connection of the output to VCC and it requires an external pull-up resistor in order to be pulled high. Looking from the schematic, there does not seem to be any connection of the outputs to a DC voltage source which may be the reason as to why the output looks strange.

    If possible, please try to simulate this circuit using TINA-TI or PSpice-for-TI and provide waveforms of the strange behavior. If you also run into issues there, I can help troubleshoot further as I have access to those two programs.