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LM5170-Q1: nFault Signal

Ju Young Woo
Prodigy 50 points
Part Number: LM5170-Q1
Other Parts Discussed in Thread: TIDA-01168

Dear, Ti.

Hello.

I'd like to get help with LM5170-Q1 IC.
Currently, for the nFault function in LM5170-Q1 IC, we have a problem that the nFault signal does not occur as high.
As I checked in another post on this site, there is no capacitor between SW pin and Breaker FET in our circuit, and there is a capacitor behind FET.
Our circuit works fine when 10kohm is applied to the syncout pin, but if 10kohm is removed, it will not work.

I think the conditions for nFault signal to fall from LM5170-Q1 IC are as follows, is that right?

1. UVLO<2.5V
2. LM5170-Q1 IC VCC<8.5V
3. Large capacitor between swpin and Breaker FET
4. High side, Low side FET failure

I'd like to ask if the nFault signal could drop for another reason.

Thank you.

  • 0
    TI__Mastermind 42191 points

    Hi Ju,

    thank you for using the E2E forum.

    Let me have a closer look into that and come back later today or tomorrow.

    Best regards,

     Stefan

  • 0
    TI__Genius 11335 points

    Hi Ju Young,

    From your description "Our circuit works fine when 10kohm is applied to the syncout pin, but if 10kohm is removed, it will not work.", I believe "MOSFET failure detection" is triggered. Can you show the schematic?

    Best Regards,

    Feng Ji

  • 0 in reply to Feng Ji
    Prodigy 50 points

    Hi, Feng Ji.

     I am sorry to say that my client does not want to disclose the circuit.

     However, our circuit does not have a capacitor between SW pin and Breaker like TIDA-01168 circuit, but there is a capacitor behind Breaker.
    In addition, the Breaker FET consists of one on the + line and one on the - line to prevent 12V reverse connection.
    Only Breaker FET configured on the 12V + line is connected to the BRKG and BRKS.
    The breakers configured on the - line at 12 volts are controlled from the fault signal and the gate is controlled by the fault signal when connected in the reverse direction.

     Also, we are composed of 4 Phase.

     Thank you.

  • 0 in reply to Ju Young Woo
    TI__Genius 11335 points

    Hi Ju Young,

    Can you draw a simple block diagram showing the MOSFETs and capacitors？

    Best Regards,

    Feng Ji

  • 0 in reply to Feng Ji
    Prodigy 50 points

    HI, Feng Ji,

    I delivered you a private message. I'd appreciate it if you could check it.

    Thank you.

  • 0 in reply to Ju Young Woo
    TI__Genius 11335 points

    Hi Young Woo,

    During MOS failure detection, the LM5170-Q1 checks the high-side and low-side MOSFETs of both channels as well as the circuit breaker MOSFETs to see if any of them has drain-to-source shorted.

    In your configuration, one circuit breaker MOSFET is missing and MOS failure detection will be triggered to pull down nFault.

    Best Regards,

    Feng Ji

  • 0 in reply to Feng Ji
    TI__Guru 58215 points

    Hello Young Woo,

    As we did not hear back from you, I expect the issue is solved and close the thread. Please post further questions below or start a new thread.

    Best regards,
    Brigitte