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UCC28950: UCC28950 SYNC

Nir Flysher
Expert 3367 points
Part Number: UCC28950

Dear Team,

Please see a question from my customer below :

Power supply (P.S) main parameters:

Input voltage:300V, Output:12V/25A.

 

I would like to synchronize the P.S to external clock in the range: 350 KHz-450 KHz. Therefore, if I understand correctly, I need to configure the controller as Slave mode.

According to the data sheet: "slave converter does not start until at least one synchronization pulse has been received".

 

In my system, this P.S is the voltage source to the pulse generator (FPGA) that provide the synchronization pulse to the UCC28950 controller.

 

Please advice, How to operate the P.S in the start up without sync, and only after the P.S output voltage is stable, and the FPGA is ready, then provide the synchronization pulses to the controller.   

 

Note: I have a start up circuit that provide the 12v bias voltage to the controller for only to 50msec (this circuit can't operate the FPGA).

 

Thanks in advance for your prompt response.

Nir.

  • 0
    TI__Mastermind 31580 points
    Hi Nir,

    I have asked one of the engineers to respond to your post. You should see a resposne later today.

    Regards

    Peter
  • 0 in reply to Peter Meaney
    TI__Mastermind 25570 points

    Hello Nir

    This is a classic chicken and egg scenario. The only solution I can think of is that you build some low power external logic to generate the first SYNC edge - something like a simple RC timer running into an OR gate. The second OR input would be the output of the FPGA. Once that initial pulse is received the UCC28950 will run through its Soft Start routine and bring the output up while running at its own free running frequency. The UCC28950 will synchronise to the FPGA output when it starts. 

    Do note: it is important to keep the SYNC PCB traces as far from the CS signal as possible to avoid the possibility of noise coupling from the edges of the SYNC signal. An additional precaution that you have would be to adjust the duty cycle of the SYNC signal so that the edges don't happen near the end of the PWM on time.

    Regards
    Colin

  • 0 in reply to Colin Gillmor
    Prodigy 10 points

    Hello,

    Thanks for your informative response.

    Gabi.k