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LM5175 - Input Capacitor Selection (for VOUT = 12 V @ 5 A)

Other Parts Discussed in Thread: LM5175, LM5175RHFEVM-HD

Hello team,

I have a support request regarding the LM5175PWP, the application is question is using the Input Capacitor configuration seen on Page 10 of LM5175EVM-HP's User Guide, including C1, a 180 µF Polymer Aluminum Electrolytic Capacitor. My guess is that LM5175EVM-HP uses that the 180 µF Electrolytic Capacitor is the Bulk Capacitor used set to support the max. current going through the input capacitors based on what I saw in Section 9.2.2.6 of the LM5175 datasheet.

Also, as a note... ‎WEBENCH® suggests using (1) Bulk Capacitor of 68 µF, and (6) Ceramic 4.7 µF capacitors.

Questions:

  1. How was the 180 µF Bulk cap (C1) selected in LM5175EVM-HP?
  2. Could this application just use four (4) Ceramic capacitors and one (1) General Purpose Bulk capacitor?
    If so, what would be the tradeoff?
  3. What would the minimum value be for the Bulk capacitor?

Application Details
Input: VIN(MIN) = 6 V, VIN(MAX) = 36 V
Output: VOUT 12 V, IOUT(TYP) = 2 A to 3 A, IOUT(MAX) = 5 A (versus the up to 10 A the HP EVM supports)

Thanks,
Victor S.