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LMR54406: How to protect again short to battery on output

Ben holter
Prodigy 200 points
Part Number: LMR54406
Other Parts Discussed in Thread: TPS7B4253-Q1

Hello, 

I was wondering if you have a reference architecture or better product to be able to handle Battery voltage (up to 36V) on the output Pin. This wont be a normal scenario, but my product requires all external pins to handle battery and ground connections, and the output of this device would be accessed on an external pin. 

  • 0
    Prodigy 200 points

    Just to add to this, the power input to the device may be battery as well, or may be floating (open circuit). 

  • 0 in reply to Ben holter
    TI__Genius 9980 points

    Hi Ben,

    I would like to refer you to the functional safety datasheet.

    For VIN shorted to ground, Current will flow from the output capacitors through the high side FET to the input short. This may or may not damage the device as it depends on how large that reverse current is, and how much COUT you have. It really depends on the specific application which is why for this device it's rated as an 'A' type failure (meaning device may lose functionality).

    I hope this helps.

    Thanks,

    Andrew

  • 0 in reply to Andrew Kutzler
    Prodigy 200 points

    Hello, 

    I am not as worried about VIN to ground, i am more worried about SW to VIN, however, lower in the document i found this:

    However, the description doesnt make sense, should this actually read damage to internal FET like some of the tables above? Or what does internal fet mean if SW is shorted to VIN?

  • +1 in reply to Ben holter
    TI__Genius 9980 points

    Hi Ben,

    Not to worry. On the previous table VIN and SW are adjacent pins, so this failure mode is also listed on this table. 

    It appears as a VIN to SW short will indeed cause damage to the internal FET.

    Thanks,

    Andrew

  • 0 in reply to Andrew Kutzler
    Prodigy 200 points

    Thanks, Do you know of any LDO's or Buck converters which can handle this short circuit? 5-36v input, >300mA output, 5v or tracking output

  • 0 in reply to Ben holter
    TI__Genius 9980 points

    Hi Ben,

    I was looking and I did find this device:

    https://www.ti.com/product/LMR33610

    I was looking around and I found one that had it listed as "possible damage to the device." It may just depend on what your loading conditions and other factors.

    I'm not sure if there's a device with a "B" as it really depends one what the loading conditions are, and other factors. 

    For example even this robust 6A device which has a "B" type failure for VIN shorted to GND. Still has an "A" failure for SW to VIN.

    https://www.ti.com/product/LM61460 

    Thanks,

    Andrew

  • 0 in reply to Andrew Kutzler
    Prodigy 200 points

    Hello,

    I think i may have found one that works short to supply, am i missing something?

    TPS7B4253-Q1

  • 0 in reply to Ben holter
    TI__Genius 9980 points

    Hi Ben,

    Unfortunately my expertise is solely on Buck Switching Regulator type products. Could you make a new thread about that device and ask your question? An engineer for that product family should be able to answer your question.

    You might also want to specify which pin you are interested in shorting to VIN as LDO's don't have a SW node.

    If you have further questions about Buck switching regulator type products, though I can help in this thread.


    Thanks,

    Andrew