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LMZ31520: Decreased power output observed

Part Number: LMZ31520

Hi,

I have designed a board with LMZ31520RLGT.

The schematics part is as below 

Please let me know if anything I have missed out here.

We are observing a 1.92V on the output, we have checked the resistor before mounting and its 324E exact.

(The design was done with a buffer of 2A from the actual requirement.)

What could be the possible reasons for low output voltage?

Thanks & Regards,

Nanjunda M

  • Hi Nanjunda,

    One thing you can do is have all PH pins shorted together using a copper area beneath pad 71. Other than that, the schematic looks fine for a 5V to 3.3V design. When you say buffer of 2A from actual requirement, do you mean the design will be running at 13A so you designed it for 15A with a buffer of 2A?

    Can you provide me startup waveform of VIN,VPWRGD and VOUT measurement to confirm that the part is properly regulating the output to 1.92V. 

    Regards,

    Jimmy  

  • Hi Jimmy,

    We have connected all the PH together in the layout.

    Yes, the board power requirement is around 13A on 3.3V rail.

    Please find the attached waveforms for your reference.

    Vin:

    Vout:

    Power Good:

    Please help us with your valuable inputs.

    Thanks & Regards,

    Nanjunda M

  • Hi Jimmy,

    The issue was with the input that we were giving. It had huge noise(ripple).
    So when we reduced that, the output was proper.

    Thanks for the guidence.

    Regards,
    Nanjunda M
  • Hi Nanjunda,

    Thank you for the waveform and update. I was actually going to ask you what power supply you were using and if it was well regulated since the input waveform didn't look stable. I'm glad I was able to help. 

    Regards,

    Jimmy 

  • Hi Jimmy,

    Yes. Thank you.

    Regards,

    Nanjunda M