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LM393-N: Input Resistance of the IC

Raj Narnoli
Intellectual 320 points
Part Number: LM393-N
Other Parts Discussed in Thread: LM393

I want to make sure that the input impedance of the input pins is high enough that it won't be affected by the voltage divider circuit I have designed here in the attached snapshot.

  • 0
    Guru 140200 points

    Hi Raj,

    the input bias current of 100nA of LM393N causes a voltage drop of 0.1V across R9. I guess that's not what you want?

    I would remove R9 and R10 and split R8 suitedly :-)

    Do you need help with this?

    Kai

  • 0 in reply to kai klaas69
    Guru 140200 points

    And add hysteresis :-)

    Kai

  • 0 in reply to kai klaas69
    Intellectual 320 points

    Yes Sure..... I would like to install 0603 resistors hence I split the values accordingly. Please help me with suitable values. The powering points MC+ And MC- are at 530V maximum and I am controlling Precharge and Accumulator Isolation Relay with this circuit. LM393 should change logic levels at 90% of the Battery Voltage.

  • 0 in reply to Raj Narnoli
    TI__Genius 10485 points

    Hi Raj,

    Depending on your desired resistor tolerance, I would suggest splitting R8 into resistances as close to a 2.45kOhm and a 24.54kOhm. (So maybe a 2.44kOhm and a 24.6kOhm?)

    To maintain the 10/11 ratio of the voltage seen at the bottom of R7, the ~2.45kOhm should be placed on the top of the voltage divider and the ~24.54kOhm should be placed on the bottom of the divider and connected to GND.

    The voltage across the ~24.54kOhm should feed the "NEG_A" input to the LM393.

    Would you still like to implement external hysteresis?

    Regards,

    Joe