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UCC27282: Broken root cause

Emma Wang
Expert 4600 points
Part Number: UCC27282

Hi expert, 

My customer is using UCC27282QDRCRQ1 first time and it is for a 300W Sync boost, the two MOSFET are CSD19502.

PWM switching frequency: 60KHz

Duty cycle: 20%（the main switch turn on for 20% time）

They increased the input voltage with no load, when the input voltage reaches 55V. UCC27282 will always broke after the Boost sync switch (T2) turned-on for a short time, along with the sync switch(T2) broken. It can see the boot scrap capacitor voltage go low quickly. And can see clearly HS have electric fire and then broken. As below picture.

And they also monitor that when the main switch is turned on, the PWM for the high switch (sync switch) can monitor a high negative voltage, which is about -12.7V (HO to HS). However, this is happened when the circuit is working normally, they just want to check whether there is risk when there is so great negative voltage from HO to HS.

The broken issue is very strange and damage many experiment boards of customer, could you kindly point the issue root cause? 

BR

Emma

  • 0
    TI__Genius 11770 points

    Hi Emma,

    That amount of negative voltage is definitely an issue, and likely what broke the driver. Here are the ratings in the datasheet:

    The abs max negative pulse for this pin is -2V, so -12V is well beyond this. 

    As for why there is such a large, negative spike on HO, we need more information to say for sure. I think the most helpful capture would be a zoom-in of HO-HS, LO, and SW simultaneously. A schematic would also help. It looks like a miller effect issue, but I'd like to be sure.

    There are a few things that can help alleviate the pulse regardless of the cause. A diode from HO to GND can shunt undershoots for example. Lowering the dV/dt of the switch node may also help, but it depends on the root cause. 

    I will mark as resolved for now, but feel free to follow-up.

    Thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    TI__Expert 4600 points

    Alex,

    Sorry forget to put the schematic, Here is it:

    And customer wants to know, large HO to HS negative voltage can cause damage to HS to GND short or not? 

    BR

    Emma

  • 0 in reply to Emma Wang
    TI__Genius 11770 points

    Hi Emma,

    With a large negative voltage on HO to HS, many things can break. The HO pulldown NMOS will conduct in reverse and can be damaged (open or short). In addition, the voltage across the pullup structure will be exceeded and destroyed also. Once this is done, the part is broken and failures can spread throughout the device. It is very hard to predict exactly what will break and whether it will fail open or short, so HS shorting to GND is possible.

     Thanks,

    Alex M.