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UCC27324: The chip is very hot

Annie Liu
Genius 10295 points
Part Number: UCC27324
Other Parts Discussed in Thread: UCC28950, , UCC27624

Hi Team,

The reference design in the customer's UCC28950 specification. The board only supplies the chip (UCC28950 and UCC27324) with 12V voltage, and the mos tube has not yet supplied high voltage, but UCC27324 is very hot. Could it be caused by the drive transformer? Turn ratio 50:50:50

Regards,

Annie Liu

  • 0
    TI__Genius 11770 points

    Hi Annie,

    This sounds like it could be a magnetizing current issue. Here are a few things to check:

    • The duty cycle is symmetrical; if OUTA is high for 5us, then OUTB should be high the next cycle for 5us. The average voltage across the transformer should be 0V or it will saturate.
    • Check magnetizing current; you can find the formula in the attached image in column 2 which will tell you the RMS magnetizing current. 

    This device uses a hybrid pullup with a very small PMOS. Therefore it has a fairly large impedance when the output is high, as the PMOS has to source all of the current:

    So you can use I^2*R with this value and the rms magnetizing current to estimate power dissipation. If you use the newest generation version of this device (UCC27624), it will have about 1/6 the resistance for pullup, and therefore less power dissipation. 

    Also, I can help calculate power losses more accurately if you can include more of the secondary side.