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UCC2897A: 54V to 12V output (with PRI AUX)

stanley wang
Prodigy 40 points
Part Number: UCC2897A

Hi Sir,

please see attached file, we use UCC2897A PWM controller.(input 54V, output 12V), 

and the design is with transformer AUX pin (output 12V/20mA) connect to UCC2897A pin 12,13 (PVDD,VDD)

when provide 54V input, there is no output 12V, and we can hear audio noise...

please help review the schematic again, and provide your suggestion...

thanks!

ucc2897a.pdf

  • 0
    TI__Mastermind 34465 points

    Hello Stanley,

    It sounds like your controller is starting up and shutting down again for some reason.

    That is why you are hearing the audio noise.

    You may not have enough voltage on the aux winding to enable the controller or you may have a LINEUV , LINEOV or over current fault on CS.

    You can disconnect the aux winding VCIN and apply 11V through a protection diode to VDD pin.
    This should enable the controller once it starts up through VIN.

    After this check the OUT pwm waveform and the VCIN voltage.

    You can only do this with a scope.

    Let me know how you get on.

    Regards

    JOhn

  • 0 in reply to John Griffin1
    Prodigy 40 points

    Hi, John,

    Yes, it seems like that the transformer AUX pin unstable, there is voltage drop when power on, and the min voltage is around 8.08V, 

    from datasheet, the VDD recommended voltage min is 8.5V, (how about pin PVDD?)

    Thanks!

  • 0 in reply to stanley wang
    TI__Mastermind 34465 points

    Hi Stanley,

    VDD and PVDD should be connected together

    Let me know if I can provide any further help.

    Regards

    John