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LM5170EVM-BIDIR: LM5170EVM-BIDIR

Steven ZF Liu
Prodigy 110 points
Part Number: LM5170EVM-BIDIR
Other Parts Discussed in Thread: LM5170

Hi TI engineer

I have a question about LM5170 evm board.

When I rework  180uF Cap from outside circuit breaker to inside, the evm board couldn't start-up. I found that circuit breaker doesn't turn on and the nFault pin is pulled low.Please advise how to let evm board start-up normally and not close fault detection function.

  • 0
    TI__Guru* 78070 points
    Hi Steven,

    Thanks for considering the LM5170. You cannot put a large capacitor at that location because it defeats the fault detection. The IC detects the fault by moving up and down the switch node with small current during detection. If there is a MOSFET short (d-s short I mean), the SW cannot be moved one way or the other. A large capacitor there would prevent the SW node from being moved to the desired threshold in the 2ms detection time.

    If you want to place the large capacitor there, you must disable the fault detection by closing the two pins of Jumper header J3 of the EVM.

    Thanks,
    Youhao Xi, Applications Engineering
  • 0 in reply to Youhao Xi
    Prodigy 110 points
    Hi Youhao,

    Thanks for your reply.
    So, I only have two choice, the first way is to put the large capacitor on the inside and disable fault detection function , the another way remain the location of capacitor on the outside and we can still use fault detection function , right?

    I don't understand what you mean that If there is a MOSFET short (d-s short I mean), "the SW cannot be moved one way or the other".
    Could you explain fault detection more detail include providing the equivalent circuit or model, and describe it how to work?
    Please tell me the desired threshold in the 2ms detection time!
    Thanks.
  • 0 in reply to Steven ZF Liu
    TI__Guru* 78070 points

    Hi Steven,

    Yes, you have only these two options.

    If the high side FET D-S short, the SW node cannot be pulled down to GND by the weak detection circuit. If the low side FET D-S short, the SW node cannot be pulled high. The threshold for the fault detection of the SW is at about 4V for high, and ~1V on the low side.

    Thanks,
    Youhao

  • 0 in reply to Youhao Xi
    Prodigy 110 points
    Hi Youhao,

    OK, I understand.

    If the circuit breaker back-to-back D-S short, can the IC detect a short-circuit fault and report?How to detect?

    The nFault pin is pulled high, the BRKG-BRKS pin is pulled low, and Vin pin is applyed 48V, however the evm board couldn't start-up. How should I debug?How to measure SD signal?

    Thanks.
  • 0 in reply to Steven ZF Liu
    TI__Guru* 78070 points
    Something does not make sense. If nFAULT is high, BRKG-BRKS should be high. Can you take a photo picture of the EVM so I can check your jumper settings?

    thanks,
    Youhao
  • 0 in reply to Youhao Xi
    Prodigy 110 points
    The problem has been solved.

    Thanks.