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TPS544C25 COUT ceramic required?

LeonardEllis
Guru 71526 points
Other Parts Discussed in Thread: TPS544C25

The TPS544C25 datasheet has an example design and details the CIN and COUT requirements.  Page 81 specifies the CIN must be ceramic, although in the example description on pg 82, it states a 100uF polymer cap was also added. 

For COUT, no such ceramic requirement is stated, only the ESR MIN must be met.  Is there a restriction for COUT to be ceramic, or can TANT/ALUM low-ESR capacitors be used?  Webench also defaults to ceramic COUT, and all the alternate devices seem to be ceramic, so is only ceramic allowed for COUT?

~Leonard

 

  • 0
    TI__Genius 11095 points

    Hi Leonard,

    There is no strict ceramic output capacitor requirement for TPS544C25, it's just a matter of stabilizing the control loop, and reducing the output ripple such that it will not corrupt operation of the load device, cause any system-level issues. Most typically, the TPS544C25 is used with mixed capacitor types, even on the input side. Some ceramic capacitance is used to drive down the effective ESR, while some polymer/tantalum capacitance is added in parallel to enable the high capacitance values typically needed for high current designs in a relatively small XY area. 

    The ceramic capacitance suggestion is not meant to say that the input capacitance should be purely ceramic, but that some ceramic capacitance is likely needed to keep the resistive part of the ripple small. Having some ceramic and some bulk capacitance is totally normal.This is needed because TPS544C25 uses the VDD pin for its high-side current sensing (assuming VIN=VDD to infer the current in the high-side FET is VDD-SW / Rds ). 

  • 0 in reply to Matt Schurmann
    TI__Guru 71526 points

    Thanks very much, Matt, and for the lightning-fast response! 

    This makes sense, to have mixed capacitor types.  I was concerned because the datasheet does make the statement about CIN " . . require a high-quality, ceramic,  . . ", so I wanted to make sure we could indeed use other types, and mix.

    Thanks,

    ~Leonard