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Back-Feed Question: design 3554830/14 LM536015QDSXRQ1

Todd Kennard
Prodigy 50 points
Other Parts Discussed in Thread: TPS2547, TPS2419, LM53601-Q1

*** ignore/delete***

This thread has little bearing on the actual inquiry I wanted to make. The basic question has been clarified and created with the base part number in another post to better match the foum. Originally, I tried several part numbers but the board would not accept them as valid. I found one that worked. 

DC-DC Switcher fixed 5V out

What is the best practice if using the device to reduce an external supply to 5VDC to power a control board with a USB connector that has 5VDC that can power the device concerning possible back-feed to the Switcher ? Does the device have any sort of back-feed protection built in ? The control board uses the USB as a programming port and is used during installation when external power is not available. It may be used for manual diagnostics which may have both supplies active at the same time. I'd rather not use a generic diode as the voltage drop may cause the control board to become unstable. The board is being fused @ 300mA with typical draw ~ 125-250mA.

The 5VDC control board has simplistic backfeed to protect the USB supply. How about the Switcher side ? Control board documentation suggests this is not an issue unless the controller is heavily stressed...

Thanks for the design tools !

  • 0
    TI__Guru**** 191445 points
    Todd,

    Why did you not fill in the part number field? Support is filtered by the part number. Not filling it in may result in delayed support. I would probably recommend a USB controller such as TPS2547 or similar or possibly a smart diode or'ing controller such as TPS2419 to interface /isolate your on board 5 V rail from the external USB 5 V.
  • 0 in reply to JohnTucker
    Prodigy 50 points

    "Why did you not fill in the part number field? Support is filtered by the part number. Not filling it in may result in delayed support."

    Because your web app did not accept the part/design number in any of the following formats as taken from the data sheet and WEBENCH .pdf files: "LM53601QDSXRQ1", "LM53601", "3554830/14", "3554830", "3554830/14 LM53601QDSXRQ1". I agree support will be better if that actually worked.

    I just tried "LM53601-Q1" and that took it.  This has become a feedback suggestion as I will reword the original question with this base part number even though it is not specific. I suggest you re-code your input filters to be a bit more flexible.