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TPS23756: Q1 (Si7119DN) was burned

Kevin Huang2
Prodigy 160 points
Part Number: TPS23756

Hi anyone who can help,

My POE schematic can be found in my previous post:

https://e2e.ti.com/support/power-management/f/196/p/811015/3002427#3002427

It's working, but yesterday I got a problem. The P-channel mosfet was burned in 10 mins after power on.

At beginning, I connect my POE with my load(about 1.5A~2A, 5V), and use the thermal camera to monitor the heat spots. Everything is normal; Q2 (Si7852DP) was about 55~60 C degree, Q4 (Si7456DP) was about 45~50 C degree. No other high temperature spot found.

But after 10 mins running, the Q1 (Si7119DN) suddenly smoked and burned. This chip was not one of the heat spots. The C2 (0.047uF, 250V, 1206) was not broken with the testing by multi-meter.

Could please tell what's the potential reason to cause it? If (just if) the Q1's gate pin shorted with the source pin, will that cause the problem?

Sincerely,

Kevin

  • 0
    TI__Expert 5615 points

    Kevin,

    I apologize for the brief delay in responding to your post.  Please expect an answer from our PD Applications Engineer today.

    Thanks,

  • 0 in reply to Thomas Lewis
    Prodigy 160 points

    Thanks Thomas,

    We have couple boards, and all are working fine except the burned one. Even for the burned one, after we replaced the burned chip(Si7119DN) and the capacitor(0.047uF 250V) I mentioned above, the board is working properly for 3 hours.

    To me, I just want to know the potential problem, and try to avoid it in our product. If that was caused by the defective single chip/capacitor only, then we will not worry about it anymore.

    Bests,

    Kevin 

  • 0 in reply to Kevin Huang2
    TI__Mastermind 41790 points

    Hi Kevin,

    The schematic looks solid (same as our EVM). Was any component changed on the PCB than what's on your schematic? Did the damage occur while you were testing something like probing, doing a load test, touching the board, performing a shutdown? Otherwise, it could have been damaged from ESD (or the FET got weaker/less robust from ESD from previous testing) such that it damaged during normal operation.

  • 0 in reply to Darwin Fernandez
    TI__Mastermind 41790 points

    Or you can take measurement of VGS and VDS of the PFET to see if in normal operation there is a repetitive large spike that is above the abs max rating of the FET.

  • 0 in reply to Darwin Fernandez
    Prodigy 160 points

    Hi Darwin,

    Thanks for you response. The MOSFET was burned during normal free running with normal load, not during any other (probing, touching, shutdown, nor so on) actions.

    Now for the board (keep running about 7 hours, still good) there is no (repetitive) abnormal spike observed.  

    Looks, and hope that just was a bad luck about that chip. 

    Thank you again, and have a good day.

    Regards,

    Kevin