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TPS92518: Ripple Current @ Analog Dimming

Sam Simonian
Prodigy 40 points
Part Number: TPS92518

If the pk-pk ripple current is set to 10% at the max output current level, then at 50% analog dimming is it 10% or 20%?

  • 0
    Prodigy 40 points
    Also, when analog dimming, is there a lower limit to the average and pk-pk ripple currents that could be set?

    Thanks
  • 0 in reply to Sam Simonian
    TI__Mastermind 28655 points

    Hello Sam,

    The current ripple is a function of the LED stack voltage not the output current. If the peak to peak current ripple is 10% at 100% analog dimming then it will be close to 20% peak to peak at 50%. The average output current will not be half of 100% because the TPS92518 regulates peak current. This means when analog dimming is set to 50% the average output current will be less than 50%.

    Regards,

  • 0 in reply to Irwin Nederbragt
    Prodigy 40 points

    Thanks Irwin,

    So, how would we set up this part if the driver requirement is such that it can be programmed from 100mA to 1A, 2V to 55V Led forward voltage and less than 30% pk-pk ripple, assuming TPS92518HV and 60Vdc input?

    One way is to set the pk--pk ripple at 3% at 1A. Is this the only way?

    Regards

  • 0 in reply to Sam Simonian
    TI__Mastermind 28655 points
    Hello Sam,

    This is quite a wide operating range, the frequency will vary a lot with 2V to 55V load. For 100 mA to 1A to be linear the peak to peak ripple will have to be 20% or less at 1A.

    If you are programming this and know the operating points you can change parameters to limit the frequency range though the peak to peak ripple will also change.

    "One way is to set the pk--pk ripple at 3% at 1A. Is this the only way?" No, 20% or less peak to peak ripple at 1A will have 200% peak to peak ripple at 100 mA which is the edge of going discontinuous. This would allow linear dimming from 1A to 100 mA.

    Regards,