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LM2907-N: The output can not adjust when the input frequency changed.

user5883945
Expert 1526 points
Part Number: LM2907-N

Hi,

  Could you help to check the sch,

the input is 50% duty cycle 2k square wave, change the frequency to 20K et. output is always 1V.

  • 0
    TI__Genius 9915 points

    Hello,

    I see you are following the reference circuit in figure 46 to clamp the minimum output voltage to 1V at low speeds. It is possible that the LM2907 is not receiving a valid signal at the TACH+ input pin, which results in the output remaining at 1V. Are you able to provide a scope capture probing the voltage at pin 1 with an oscilloscope? 

    Regards,

    Zach