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LM20333: LM20333MH

Ravindra Gudi
Prodigy 50 points
Part Number: LM20333

I am using a DC-DC converter IC LM20333MH in my product design. I had built 4 boards during Feb and all those 4 boards are working without any issues. There was no problem for the power supply bring-up as well.

I got built 2 more sets of same design board yesterday. The DC DC converter IC is not able to provide proper output. Upon checking status of all pins on the working board and non-working new board, I see that all the pins probing gives the same voltage values except for BOOT pin. This pin is unable to provide proper switching frequency. Attached are the oscilloscope screenshot for BOOT pin probing. Screen shot of the schematics is also attached.

Can you please help me with resolving this problem? 

Regards,

RaviLM20333MH Issue.zip

  • 0
    TI__Expert 8245 points

    Hi,

    Firstly please double check every components are same between working and non-working boards. It should be caused by some errors on components or assembly.

  • 0 in reply to Iven Su
    Prodigy 50 points

    Thanks Iven  for the reply.

    I did check in the beginning itself between the two boards for the circuit components. All of them are same. Assembly of the parts is also correct and i didn't find any solder issue.

    Actually i measured the voltages at all the pins of the two boards - here is the summary. The measurements were taken with 6 1/2 DMM, so you will see the RMS values here.

    Is there any possibility that internal to the IC - something gone wrong?

    Regards,

    Ravi

    Spin-2-PowerSupply-Issue.xlsx

  • 0 in reply to Ravindra Gudi
    TI__Expert 8245 points

    Hi,

    It looks the boot capacitor are not well charged, I don't think it makes any sense that the first ones are all good and the second are all not. So please swap the boot capacitor C11 between working and non-working boards. If no effect, just swap U27.

  • 0 in reply to Iven Su
    Prodigy 50 points

    I did the check on the feedback resistors one more time and found that on of the resistor was not correct - it was 20ohm instead of 60.4K ohm. with this change I am not getting proper output voltage. The pack of 60.4K resistors were all measured to be 20 ohm when checked.

    Thanks for looking into the problem and your suggestions.

    Regards,

    Ravi