LMR33630: output capacitor howling

Betty Guo

Expert 7300 points

Part Number: LMR33630
Other Parts Discussed in Thread: LMR36015,

Hi team,

below is customer schematic, they found the output capacitor will howling when connect load.

customer application as below:

1. input 12V, output 4V/1Amax , usually output current is 300mA, fsw=400kHz

2. inductor L0203 Irms =3.5A, Isat =6A.

4. output capatior 22uF rating voltage is 10V.

3. change R0250 and R0251 to 33K and 11k, still howling.

I also attached SW waveform and output ripple waveform and PCB layout, could you help give some suggestions? thanks

LMR33630 waveform.zip

over 5 years ago

0 Daniel Li14 over 5 years ago

TI__Mastermind 27470 points

Hi Betty:

I think under 400mA load , the device is switching between DCM mode and Auto Foldback. can you try to 6.8uH see any improve? or you can try LMR36015 with same pacakge.

Thanks

0 Betty Guo over 5 years ago in reply to Daniel Li14

TI__Expert 7300 points

Thanks Danile,

one quesiton What's the difference between using 6.8uH and 10uH? and what the current threhold of LMR33630 to entern PFM?

0 Daniel Li14 over 5 years ago in reply to Betty Guo

TI__Mastermind 27470 points

Hi Betty:

using 6.8uH will make the device at 400Khz in DCM mode. you can use below tools to check DCM, Auto Foldback and FPM.

Power management

Power management forum

LMR33630: output capacitor howling