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Original question:

UCC28782EVM-030: UCC28782-030 SR REGULATOR

UCC28782: UCC28782- DITHERING

robin gangopadhya18
Mastermind 6050 points
Part Number: UCC28782
Other Parts Discussed in Thread: UCC24612, UCC28780

Jaden:

re: UCC28782 DITHERING FUNCTION.

Any means by which we can keep dither disabled until application/EMI tests tell us to enable it?

-r

  • 0
    TI__Mastermind 26840 points

    Hello Robin, 

    The frequency-dithering function of the UCC28782 is hard-programmed into the controller and cannot be disabled by any external means. 
    Dithering is enabled for Ivsl currents > 646uA, which is usually at the higher input line voltages.  the function "fades out" and is disabled when Ivsl < 580uA.

    For the typical "universal line" input application this corresponds roughly to a 140-Vac transition boundary.
    Actual input voltages depend on the transformer primary-to-auxiliary turns ratio and the upper resistor value on the VS pin.   

    So generally, there is no dithering during low-line operation because the bulk ripple voltage already accomplishes significant frequency deviation to spread the EMI signature.  Dithering is added at higher lines where the bulk ripple is relatively low. 

    Regards,

    Ulrich

  • 0 in reply to Ulrich Goerke
    Mastermind 6050 points

    Hello Ulrich

    As usual appreciate your response: right on!

    So glad to hear back from you...

    Happy New Year BTW.

    So we had to hop out of UCC28780/UCC24612 wagon & hitchto UCC28782/MP6908...hope we can handle the dithering events which we will have to test especially for any unforeseen events.

    r

    BTW: our previous pcb turned out to have 3 vias to GND plane causing all the problems! This time, we are duplicating 28782 eval kit copper plane, placement of critical parts & routing. fyi

  • 0 in reply to robin gangopadhya18
    Mastermind 6050 points

    In reply to Ulrich Goerke:

    Hello Ulrich

    As usual appreciate your response: right on!

    So glad to hear back from you...

    Happy New Year BTW.

    So we had to hop out of UCC28780/UCC24612 wagon & hitchto UCC28782/MP6908...hope we can handle the dithering events which we will have to test especially for any unforeseen events.

    r

    BTW: our previous pcb turned out to have 3 vias to GND plane causing all the problems! This time, we are duplicating 28782 eval kit copper plane, placement of critical parts & routing. fyi

  • 0 in reply to robin gangopadhya18
    TI__Mastermind 26840 points

    Hi Robin,

    I guess this is a duplicate thread, as I have replied to the other one.

    I will close this one.

    Regards,

    Ulrich