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LM5175: How are Quantity and sizes of Capacitors Chosen?

Jim Fuoco
Prodigy 220 points
Part Number: LM5175

I've played around with the WeBench tool quite a bit in the last year coming up with PSU designs. One thing I've noticed is they tend to spit out designs with more small capacitors, rather than condensing them into fewer, larger capacitors. For instance the design below (12 V, 8 A out) ends up with 9x 22 uF 1210 Caps, roughly 200 uF total output capacitance:

BOM: 

How are these quantities and sizes chosen? Are they optimizing for cost, or something else? If board space is at a premium, can I simply replace with 2 100 uF caps and be on my way? Seems to unnecessarily add a lot of parts to the total component cost and PCB layout.

  • 0
    TI__Mastermind 46905 points
    Hi Jim,

    It is not easy to find a 100uF in the market (with high voltage) or the package could be very large. and the layout may be not optimized if only select only large package capacitor. i normally select small capacitor and large cap in parallel.