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LP339 Common Mode limits

Matthew Brown
Prodigy 90 points
Other Parts Discussed in Thread: LP339, LM239

Hello,

I'm using the LP339 in a motor control application to sense BEMF voltage levels and detect zero crossings.  The inputs could see large common mode voltages.  Vicr is recommend for 0V to Vcc-2.   What happens above that recommended Vicr limit?  Do I risk damaging the device or just an indeterminate output?

In my design Vcc = 12V and the common mode voltages could go to 15V.

Thanks for any guidance!

-Matt

  • 0
    TI__Guru**** 157016 points

    Matthew,

    The inputs can tolerate -0.3 to 30V (36 abs max). As long as one input is in the recommended voltage range then the output will be the correct state.
    Below -0.3V would require a current limiting resistor and the output may be in the wrong state.

    Regards,
    Ron Michallick

     

     

  • 0 in reply to Ron Michallick
    Prodigy 90 points

    Great - thanks Ron!

  • 0 in reply to Ron Michallick
    Prodigy 145 points
    Hi Ron,

    Could you please ehelp understand what happens when one of the input to LM239 is below -0.3V
    "Below -0.3V would require a current limiting resistor and the output may be in the wrong state."

    Does the current limit resistor prevent damage or can it ensure proper operation if proper resistor is placed in series with the input.. Any guidance on how to calucate the value of the resistor.
    LM239 is powered by 12 V and has a 1Kohm resistor in series with the non-inverting input.

    Thank you,
    Ravi
  • 0 in reply to Ravi John
    TI__Guru**** 157016 points

    Ravi,

    The resistor prevents damage. The resistor won't prevent a temporary malfunction in the output.

    It take only a little input current to get an output malfunction.

    Phase Reversal.pptx