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Two Output Capacitors Specified... Parallel or Serial?

Marc Nussbaum
Prodigy 50 points
Other Parts Discussed in Thread: TPS61175

I used SwitcherPro do design a boost regulator using the TPS61175. The output capacity is specified by the program as being "15uF x 2".

Are these two caps to be connected in series or parallel?  I would expect in series as the drawn schematic shows a single capacitor symbol. However, when I try to substitute a single 15uF or single 22uF cap that otherwise meets the current, voltage, ripple and ESR requirements SwitcherPro tells me the loop margin is unacceptable. If I specify a single 33uF cap, the software is happy. Now I know that two caps of the same value in parallel is equivalent to 1/2 one of the capacitors from a charge-capacitance standpoint. This would imply that the software wants the two 15uF caps in parallel. Not at all how the schematic is drawn by SwitcherPro.

Which is the right way to connect the two 15uF caps recommended by SwitcherPro?

 

Thanks, Marc

 

  • 0
    TI__Intellectual 1280 points

    Marc,

    Thanks for your feedback.  For this schematic you need to connect the Output Caps in Parallel.  Sorry for the confusion.  I'll work with my team to see if there is a better way we could note when something of multiple qty is connected in series or parallel.