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LM25576: LM25576 - IS pins (15, 16) forced low

Habibi
Prodigy 70 points
Part Number: LM25576

Hello,

I have a typical LM25576 circuit, which is a new iteration of a previously working design.

The circuit fails to start and I have found that the IS pins, 15 and 16 are being shunted to PGND. I was hoping to get some help in undrstanding why this is happening.

Thanks in advance

  • 0
    TI__Mastermind 25590 points

    Charlie,

    The IS pins should have a voltage very close to PGND since they are connected to PGND through a low-value current-sense resistor. Can you please share the schematic and some waveforms to show what you've tried and how exactly the part isn't working?

    Thanks,

    -Sam

  • 0 in reply to Samuel Jaffe
    Prodigy 70 points

    Hi Sam,

    Yes sorry, I was looking for shorts rather than measuring the resistance. I think I fried the chip when moving it from another board, I have put in a new one and getting some results.

    It appears the circuit is working as designed, but the switch output is oscilating, at about 3Mhz it seems. I have attached the circuit I am working from, not included is a voltage multiplier that goes off screen.

    I believe I have used the correct compensation as suggested in the datasheet. I might roll back to a previous PCB and see if an error has occured since then.

    Thanks for your help

  • 0 in reply to Habibi
    TI__Mastermind 25590 points

    Habibi,

    Sure thing! Once you check again, let me know if I can be of further assistance.

    Note** threads lock after 30 days so you may want to start a new thread. Thanks!

    -Sam