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UCC21750-Q1: Ucc21750 trigger DSAT randomly

Yuhao Wang
Prodigy 330 points
Part Number: UCC21750-Q1
Other Parts Discussed in Thread: UCC21750,

Ucc21750 customers may trigger DSAT after powering on, the waveform is as follows：

the yellow curve is the ge the blue line is the input and the green curve is ce, the purple curve is dsat.

  • 0
    TI__Genius 15146 points

    Hi Yuhao,

    Is green the V(collector) to V(emitter) votlage? It looks like DESAT is correctly turning off for a high Vce voltage.

    It looks like something goes wrong with the yellow V(gate) to V(emitter) voltage a dozen cycles or so before Vce starts to ramp. 

    My interpretation is that the gate is gets damaged that cycle, and starts conducting high direct current, but the IGBT still is closing. After about a dozen cycles, the gate shorts even more, and the IGBT stops closing at all. Then, the DESAT circuit has nowhere to drain the 500uA, and eventually the dsat triggers.

    What is the IGBT that you are using? You might need to use a TVS diode right across the gate to protect it from damage in this circuit. It looks pretty noisy!

     Also, it would be helpful to probe the power supply of the gate driver to see if I am right about the short. You might see a dip that coincides with the V(ge) ON pulse.

    Why does IN stop after DESAT? Shouldn't it keep pulsing since it is an input, and doesn't know that DESAT has triggered? Do you report the fault to the uC and then stop sending the pulses maybe?

    Best regards,

    Sean

  • 0 in reply to Sean Cashin
    TI__Prodigy 330 points

    Hello Sean,

    Yes, the  green curve is V(collector) to V(emitter) voltage. The circuit is shown above. This problem follows the UCC21750-Q1.

  • 0 in reply to Yuhao Wang
    TI__Genius 15146 points

    Hi Yuhao,

    Do you mean that the IGBT is undamaged? And using a different UCC21750 unit eliminates this behavior? Do you think it is a device manufacturing defect? 

    Best regards,

    Sean

  • 0 in reply to Sean Cashin
    TI__Prodigy 330 points

    Hello Sean, Yes the IGBT is undamaged, using a different UCC21750 unit eliminates this behavior. This could be a manufacturing defect, however the desat could be triggered only on the certain position of the system which is weird.

  • 0 in reply to Yuhao Wang
    TI__Genius 15146 points

    Why is Vce so low? Are you trying to use this with negative voltage across the IGBT?

  • 0 in reply to Sean Cashin
    TI__Prodigy 330 points

    Bus voltage is not connected. Can I send you the chip or we can have a meeting to discuss this problem.

    Thanks,

    Yuhao

  • 0 in reply to Yuhao Wang
    TI__Genius 15146 points

    We can set up a meeting if you want. You can send me a webex or teams link.

    If the Bus is not connected, where is this voltage coming from? Do you have a problem with your bootstrap supply? It would help me if you share your schematic.