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LM20146: LM20146MH issue

Roy wang
Intellectual 775 points
Part Number: LM20146

Hello,

I used LM20146 some question,

The input voltage is 5V，but the output voltage is 0V，no voltage.

The FB pin voltage is 0V.

I can not find the issue，please kindly help to check the  SCH.

l

  • 0 in reply to Roy wang
    TI__Guru**** 191445 points

    Roy,

    I don't see anything obviously wrong with your schematic. It looks like you just copied the datasheet example. One thing I do note is I do not see a value for C40. It is requires for proper operation.

  • 0 in reply to JohnTucker
    Intellectual 775 points

    Dear John,

    C40 = 100nF，

    Yes, I copied the datasheet example, and the pcb Component placement Value is the datasheet Recommended value.

    It same as the below picture.

  • 0 in reply to Roy wang
    TI__Guru**** 191445 points
    Roy,

    If the schematic is identical and you followed the PCB layout recommendations as well, then most likely there is a wrong component or a soldering defect. You will have to manually troubleshoot it. How many systems have you built and how many of those show the issue? The first thing I would do is a thorough visual inspection. Then you can slowly raise the input voltage until the circuit is enabled. Look to see if the SW pin ever gets any proper switching pulses. Dose the circuit output voltage ramp up then collapse? Or does it never switch at all? Check the voltage and waveform at each pin to look for unusual levels or activity.