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TPS92691-Q1: Syncing 20 devices to the same clock

David Naviaux
Intellectual 590 points
Part Number: TPS92691-Q1

I would like to synchronize the clocks of 20 TPS92691-Q1 from a clock pin from a microcontroller.  The datasheet does not seem to give enough information on the RT/SYNC input to design an appropriate clock driver circuit.  How might I do this?

Thank you, David

  • 0
    TI__Mastermind 18890 points

    Hi David,

    Please see section 7.3.2 (page 12) of the data sheet. 

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Intellectual 590 points

    Tuan,

    I had previously read that part of the datasheet.  It still was not clear to me how to sync 20 of the controllers.

    If the recommended 100nF capacitor is completely charged and discharged to and from 3.3V at a 300kHz rate, it would require 6W just to drive the sync inputs so I am assuming that I do not understand the input characteristics of the RT/SYNC pin.

    It would be helpful to know what the RT/SYNC pin characteristics are.  I need this information so that I can guarantee that the my sync signal can force the 1.8V to 3.1V required thresholds through the 100nF capacitor at the pin.

    Do you have some more specifics about the RT/SYNC pin (i.e. impedance, what a scope would show if it were connected to the pin, etc.).  

    Thank you,

    David

  • 0 in reply to David Naviaux
    TI__Mastermind 18890 points

    David,

    The Caps do not charge or discharge as you mentioned.  It's just use as an AC coupling cap...This is circuit analysis here.  The load to you drive is actually total Rt resistance.  If you have Rt as 26.1K for your 300KHz then the actual load for your driver is the twenty 26.1k Ohm in parallel. 

    I hope this makes sense if not then please simulate the circuit where input impedance of Rt can be assume to be high and ignored.

    Thanks Tuan

  • 0 in reply to Tuan Tran74
    Intellectual 590 points

    Tuan,

    My experience with oscillators that set their frequency with a resistor has been that the internal circuitry is relatively complicated, differs quite a bit, and has some impedance.  I will simulate the circuit as you suggest.

    Thanks,

    David