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TPS549D22: TPS549D22 meets Vout Non-Monotonic start up with DCAP mode

Frank Xiao
Genius 12055 points
Part Number: TPS549D22

Hi team,

My customer is using the TPS549D22 now, and meets Vout Non-Monotonic start up. The RC of RCC R=1kohm C=100nf Load=2A, When change to DCAP3 mode, it works well. Do you have some ideas or experience about the phenomenon? Thanks.

  • 0
    TI__Prodigy 420 points

    Frank,

    Why did the customer select the DCAP operation? With DCAP operation, you will need to add additional RCC network across the output inductor. Based on my experience, if the RCC network produces large compensation, the output startup might not be very linear. My suggestion is to use DCAP3 if it works for the customer. 

    thanks,

    Sue

  • 0 in reply to Xiao Xu
    TI__Genius 12055 points
    Xiao,

    Thank you for your reply.

    DCAP reasons:

    1. The customer is familiar with TPS533XX series before.
    2. Large insertion ripple may give better jitter performance.

    I am also curious about why we keeps the DCAP and DCAP3 in one chip when do the definition too.

    Based on my experience, if the RCC network produces large compensation, the output startup might not be very linear.

    Do you mean the large insertion ripple above?

    BTW: Whether TPS533XX series also have the problem too?
  • 0
    TI__Prodigy 420 points
    Frank,

    The reason to have both DCAP and DCAP3 is flexibility. For customers who would like to use POSCAP for output capacitors, the DCAP topology works well for them (due to large ESR and no need for additional RCC compensation). So it is an option for certain customers.

    And yes, if the insertion ripple is large, the transient response is slow and crossover bandwidth is small, therefore, the startup might not be as linear as it should. TPS533xx series works the same way.

    thanks,

    Sue