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TPS54260: does not step down

moshe jacobson18
Expert 2210 points
Part Number: TPS54260

Hi

I am using a TPS54260DGQ in an EVM to drive a RS232 - TTL converter board. I have the circuit as per typical application 8.2.1 in the part datasheet.
My Vin is 11.5V and the desired output is 3.3V......BUT MY OUTPUT IS 11.3V!!
This has happened on 2 prototype boards...i doubt BOTH TPS parts are faulty which means that something is wrong with what i have done on the circuit. How can i establish where the problem could be?

thanks in advance...

  • 0
    TI__Guru**** 191445 points
    Abs max for EN is 5 V. Try removing R12. Let us know if that fixes the problem. You may have to replace U4 as it may be damaged.
  • 0 in reply to JohnTucker
    Expert 2210 points

    Hi John

    Thanks for answering..i took your advice.
    However, i misled you (& myself).

    Based on your response i looked at what was coming in to EN and saw that it was 5.8V which really puzzled me...taking a ohm reading i saw that the resistance between the EN pin & GND was 250K, i have no idea why that is unless its the EN pin, but whatever it is it actually saved the TPS.

    In addition, unbeknownst to me, the point where i was checking the PH output was not connected to R65 but to the 12V net itself due to the layouts not conforming to the schematics.

    So i took your advice & removed all connections to EN thus leaving it floating (& safe from further errors) & notified the layout person to rectify their error of what was connected to what after the R65.

    Thank you...
    Lesson learned:Carefully read the datasheet; Carefully check the PCB drawings!