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UCC28251: External Synchronization

Igor Tyshkov
Prodigy 115 points
Part Number: UCC28251

I need to start with RT frequency. An external frequency will be applied after some time. I  look for recommended circuit of external syncronization to 3.3V 50% Duty cycle source. RT frequency must be not affected by turn off the external frecuency.

  • 0
    TI__Genius 13660 points

    Hi Igor,

    The synchronizing signal can directly input to RT pin, the UCC28251 aligns the turn-on of primary outputs OUTA and OUTB to the falling edge of the synchronizing signal, If the frequency source is from the gate outputs of another half bridge controller, interleaving can be achieved.
    Please refer to section 8.3.4 as follows.

    Regards,

    Teng

  • 0 in reply to Teng Feng
    Prodigy 115 points

    Hi, Teng.

    The circuit can product "1" or "0" logic level signal on external clock line and i think this may affect the initial RT frequency because of RT short circuit to 0V or 3.3V.

  • 0 in reply to Igor Tyshkov
    TI__Genius 13660 points

    Hi Igor,

    Yes, once RT pin detects the synchronizing signal, the internal oscillator will synchronize to the external frequency source in the next period. Thus if you want to keep UCC28251 running at initial internal frequency for a specific time even with an external synchronizing signal input, maybe some extra circuit need to be added to disable the external synchronizing signal during the time.

    Regards,

    Teng