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TPS25944A: eFuse damage when hot swapping

Paul Barker
Prodigy 265 points
Part Number: TPS25944A

I've designed a board with TI DSP and Altera FPGA, power management, and memory ICs.  I put the TPS25944A eFuse on the front end of the board so that everything downstream is protected from hot swap issues when plugging the board into +12V DC. 

The eFuse is doing a great job protecting all ICs on the board as the +12V is connected.  However, there is nothing to protect the input to the eFuse when connecting it to a hot +12V DC.  An oscilloscope shows a +25V transient ringing when the +12V DC is connected to the board.  This has destroyed the eFuse IC on all 6 of my prototype boards since the eFuse has an absolute maximum rating of only +20V.  The inductance of the +12V DC power cable and the small input capacitance on the input side of the eFuse circuit has formed an L-C circuit that rings when +12V DC is first connected.

I implemented a simple R-C snubber on the input and this has fixed the issue.  However, I will need to respin my board to make this a part of the design.  I didn't see anything in the datasheet that warned or discussed this issue and I want to make sure this doesn't happen to others.  Also I want to verify that an R-C snubber is the best approach for this problem, or should I use a zener diode to clamp the transient below +20V, or is there another better solution that TI recommends?

Thanks,
Paul Barker
(Digital Light Processing Group, TI)

  

  • 0
    TI__Guru** 105711 points
    Hi Paul Barker,

    Thanks for reaching out and the detailed posting on the problem, solution.
    Any kind of solution to limit the input transient voltage peak would work here. The choice depends up the amount of the trace inductance in the input path.
    We recommend to use TVS diode as close as possible at the input pins of TPS25944A device. It is covered in section 12 and section 13 of the datasheet as transient protection and layout guidelines. Since, this is usage specific and system interface dependent we have not detailed much with an application example. Please go through Section 12,13 and let us know if more explanation is needed.
    Thanks
    Rakesh
  • 0 in reply to Rakesh
    TI__Prodigy 265 points
    Hi,

    Thanks for the very quick response. I had looked at sections 12, 13. Does TI have a recommendation for a TVS diode on the input that will protect from a positive transient above 18V but sill allow up to 16 Volts into the eFuse? What part is recommended, or can you point me to a web page where I can look through the different options?

    Thanks,
    Paul
  • 0 in reply to Paul Barker
    TI__Guru** 105711 points
    Hi Paul,

    SMBJ16A-13-F is a 16 V rated TVS diode and starts clamping at 17.8 V. This is appropriate part for your requirement.
    Please refer www.diodes.com/.../ds19002.pdf in case you like to choose different rating.

    Thanks
    Rakesh