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TPS40200: Synchronous function for TPS40200

Hardy Zhou
Intellectual 1650 points
Part Number: TPS40200

Hi all

    Under circumstances where the input voltage is high and the duty cycle is less than 50%, a Schottky diode connected from the RC pin to an external clock may be used to synchronize the oscillator. The cathode of the diode is connected to the RC pin. The trip point of the oscillator is set by an internal voltage divider to be 1/10 of the input voltage. The clock signal must have an amplitude higher than this trip point. When the clock goes low, it allows the reset current to restart the RC ramp, synchronizing the oscillator to the external clock. This provides a simple, single-component method for clock synchronization.

 so i want to know if any duty limited(minimum and maximum duty) for external synchronous signal, and the synchronous signal driver capability requirement  to charge the C of RC oscillator.

and if i want to use BSS83 in EVM board for synchronous function, any other special design detail i should take care of?

 Great thanks.

  • 0
    TI__Mastermind 25590 points

    Hardy,

    The previous paragraph in the datasheet goes into detail on the required signals:

    When synchronizing the oscillator to an external clock, the RC pin must be pulled below 150 mV for 20 ns or more. The external clock frequency must be higher than the free running frequency of the converter as well. When synchronizing the controller, if the RC pin is held low for an excessive amount of time, erratic operation may occur. The maximum amount of time that the RC pin should be held low is 50% of a nominal output pulse, or 10% of the period of the synchronization frequency whichever is less.

    BSS83 looks fine for this application.

    -Sam