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TPS53318 cout selection

Other Parts Discussed in Thread: LMZ22008, TPS53318, TEST, PMP7828

Dear Sir/Madam,

I am looking at TPS53318 to replace an existing LMZ22008 design.

Previously I have achieved very low output ripple < 20mV pk-pk @ 8A using low ESR polymer capacitors. 

Page 7 has two figures that show typical configurations for
ceramic output capacitors and bulk output capacitors. 

The TPS53318 EVM and reference designs only uses ceramic capacitors for Cout.

The PMP7828 RevA Test report shows very low output ripple using only ceramic capacitors.

I am trying to understand if the TPS53318 is better suited for ceramic or polymer capacitors.
That is, is there any benefit in using polymer capacitors for Cout instead of ceramic capacitors.

If i was to head down the Cout polymer capacitor path then would it be correct to say that i would
use figure 2 and not use ROVP?

If there are any reference designs using polymer capacitors or advice i would be most greatfull.

Regards Grant

  • TPS53318 uses DCAP control.  DCAP relies on ripple voltage on the VFB pin for the hysteretic off time comparator.  This ripple typically comes from the ripple voltage of the ac inductor current x output capacitor ESR.  If low ESR capacitors are used such as ceramics are used, then you need the ripple injection of R7, C1 and C2 of figure one.

    ROVP is independent of output capacitor types.  You can use it or not as you see fit.

    I do not see any reference designs for polymer capacitors.  If you are using low ESR types, you may want to stick with the ripple injection technique of figure 1.

  • Hi John,

    Thank you for the detailed reply.
    I will make the modification to the EVM before committing to low ESR polymer capacitors.

    Regards Grant