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Original question:

UCC28180: heating issue at higher switching frequency

UCC28180: PFC startup burned

Chris Peng
Prodigy 560 points
Part Number: UCC28180

Tool/software:

Dear friend,

Customer made a PFC demp using UCC28180D. However, during the test, it was found that the PFC power tube and UCC28180D chip are easily burned when the power is turned on. It may burn out once every 30 times when the power is turned on. But once it is powered on, there is no problem and it can work normally. 

The damaged chip looks like pins 7 and 8 are short-circuited, and pin 7 seems to be damaged as well.What may be the reason? 

  • 0
    TI__Expert 5005 points

    Chris,

    Just to clarify, do you mean 1 out of 30 times of power on, the chip will be damaged? What is the power tube?

    How many piece of system has the customer tried on? Can you please share us some waveform? Like pin 7 and 8, with Vin?

    How soon will the IC be burned after AC is applied, if it burns?

    Thanks,

    Ning

  • 0 in reply to Ning Tan
    TI__Mastermind 32500 points

    Hello Chris, 

    Very often when the MOSFET fails, it fails in a way that high voltage appears at the gate terminal and this high voltage then causes the UCC28180 controller to also fail. 

    In the schematic diagram, I see that your inrush protection component RT1 is a PTC device.  This means that at power up, the inrush surge heats the PTC and its resistance goes UP, not down.  That means that the inrush charging of the output capacitors may not be complete before the relay MC1 is activated and closes across RT1. 

    If peak charging of C1 and C2 is not complete before MC1 closes, then there can be another high-current surge through the bypass diode D13 but this diode (US5MC) has a high forward voltage so some of the surge current can divert into the inductor path.  If the PFC controller begins to operate and drive MOSFET Q2, the excess current may saturate the inductor and overstress Q2, sometimes to failure. 

    Q2 is a very large MOSFET and may be difficult to turn off quickly.  Also, the 5mR sense resistor R33 can allow a very high peak current before triggering OCP.

    My first advice is to change RT1 from PTC to NTC so that its resistance goes down as its temperature goes up. 
    My second advice is to add a little time delay (maybe 10~20ms) to activate MC1 so that peak charging of C1 and C2 can be sure to be complete before closing the relay. 

    What are the basic design specifications for this PFC, please?  Min/max input voltage and maximum output power?

    Regards,
    Ulrich