LM5117: LM5117

Note: Schematic Image and *.pdf both are attached.

Hello,

Thank you for sharing this information and your schematic.

I reviewed the schematic and please see my feedback below.  Based on my review, I believe that a potential problem is that the design is unstable.  Based on my calculations, I think the Compensation components should be updated and potentially the output capacitors.

1. What are the cpacitance and ESR alues for C1 and C2.  I only see 220uF listed.  Are both capacitors 220uF?  By below recommendations may alter based on this value.

2. RComp (R14) should not be greater than 40kOhm.  I recommend using a 4.6kOhm resistor.

3. CCompm (39) should be approximately 10300pF.

3. CHF (C12) should be between 14pF to 145pF with the above two changes.

Attached is the calculator tool with my selections.

Best Regards,

Katelyn Wiggenhorn

6864.7-12-18-TPS54360-361FAMILY_CALC_TOOL_REVE.xls

Hello Katelyn,

Thank you for your reply.

1) C1 and C2 both are same values capacitors. having ESR 0.20Ohm, with 220uF/50V.

I will update the Rcomp, Ccomp & CHF values as per your recommend, will update you.

Hi Katelyn,

I have changed the Rcomp, Ccomp & CHf value as per your recommend,
Rcomp = 4.7KOhm
Ccomp = 10nF
CHf= 100pF.

But still issue is not resolved.

you had attached calculator tool for TPS54360-361 family but is this same for LM5117 ??

Hello,

Thank you for trying this additional test. This is my mistake using the TPS54k calculator, I meant to use the LM5117 calculator.  Please see the appropriate recommendations below:

Could you also please share waveforms of SW, VIN, and VOUT of the below two cases:

Hello,

I want to follow up on your questions. Were you able to take the additional measurements with the new compensation values?

Best Regards,
Katelyn