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Using and external frequency source with a LM21305.

Robert Curtis
Intellectual 430 points

Hello,

I am using a 800KHz external sync source.

My  question is does the internal frequency lock to the external frequency?  There isn't any PLL in the block diagram, so I am wondering if the internal frequency will lock up to the external frequency.

Thanks for any help.

  • 0
    TI__Expert 8165 points

    Yes it does. For more info see section 8.3.3 of the datasheet.

    Regards, Davor

  • 0 in reply to Davor Glisic
    Intellectual 430 points
    Hello,

    How does the external sync source relate to the regulator's operation when in DCM? I have an application where I am experiencing low frequency acoustic (vibration) interference that appears to be coming from the regulation circuit. I am speculating that the PWM of the regulator is producing low frequency vibration in the regulation circuit (inductor), as the result of electrical frequency variation. The vibration frequency can be altered by changing the regulator external sync frequency.

    If the PWM produces asynchronous electrical switching noise, what is the external synchronization signal actually used for?

    Regards,

    Rob Curtis