LM5116: Buck converter getting hot and inductor making knocking sounds

Mohammad Tahir

Part Number: LM5116

Hello Experts,

I created a small buck converter with an input rating of <100V and an output of 5V @ around 7A.

The buck works for low currents < 1A but if more current is pulled, the PCB gets extremely hot, including the LM5116 getting hot, and the inductor starts making knocking sounds.
Could you please help me troubleshoot.

Heres the schematic and board layout:

LM5116pdf.pdf

Thank you.

Mo.

over 1 year ago

0 EricLee over 1 year ago

TI__Mastermind 46081 points

Hello Mohammed

You first have to find what causes the knocking sound. It can be caused by 1)TSD 2)Current limiting 3) instability

1) Monitor VCC.

2) Capture inductor current waveforms

3) Capture inductor current waveforms. If any oscillation, retest after reducing the crossover frequency. Use 0.1 x RCOMP and 10 x CCOMP.

-EL

0 EricLee over 1 year ago in reply to EricLee

TI__Mastermind 46081 points

4) Please retest after shorting SS5P10-M3/86A

Thanks

-EL

0 Mohammad Tahir over 1 year ago in reply to EricLee

Prodigy 40 points

Thanks Eric. So you think the Diode might be causing this? What might be your reasoning behind this?

0 Mohammad Tahir over 1 year ago in reply to EricLee

Prodigy 40 points

Thanks I will try this.

0 EricLee over 1 year ago in reply to Mohammad Tahir

TI__Mastermind 46081 points

Hello Mohammed

Please share your test results when it is ready. If possible, please share some waveforms too.

-EL

0 Mohammad Tahir over 1 year ago in reply to EricLee

Prodigy 40 points

Hello Eric, I was able to solve the overheating LM5116 issue by providing power through the output to VCCX. Now the IC runs cool. Now the only issue that remains is the Inductor still gets hot. It goes above 100C in a min. Could you please advise simple troubleshooting steps. thank you.

0 Mohammad Tahir over 1 year ago in reply to Mohammad Tahir

Prodigy 40 points

Eric, talking about Inductors, I am using 2 design tools from TI and they both seem to be off by quite a lot!
The LM5116 quickstart quide recommends an inductor of 4.8uH (which i am using and is overheating):

but the webench tool spits out an inductor value of 47uH, 10 times that of the other tool! Could you please recommend what inductor to use and which tool is accurate?

Thanks.