LM25085-Q1: LM25085-Q1

ELVIS SUN

Part Number: LM25085-Q1

Dear ,

i use LM25085-Q1 to build one DC-DC , 15V,18-25V input, and when output current larger than one current( 2A for example), the drv will keep low for hundred us, and FB pin thus abnormal cause of the ripple injected.

drv, and FB signal(abnormal and normal both)as listed below. i tried to update the injected RC, but seems no change. do you have similar waveform before, seems strange, any advice on the root cause?

over 3 years ago

0 ELVIS SUN over 3 years ago

Prodigy 20 points

add the sch here.

0 Timothy Hegarty over 3 years ago in reply to ELVIS SUN

TI__Guru 61007 points

Hi Elvis,

Please check your values using the LM251085 quickstart calculator: https://www.ti.com/tool/LM25085-5085QUICK-CALC. Check the inductor ripple current, could be current limit engaging if the issue is occuring above a certain load current. The injected ripple to FB should be in the 50-100mV range.

Regards,

Tim

0 ELVIS SUN over 3 years ago in reply to Timothy Hegarty

Prodigy 20 points

0 ELVIS SUN over 3 years ago in reply to ELVIS SUN

Prodigy 20 points

Hi Tim,

0 ELVIS SUN over 3 years ago in reply to ELVIS SUN

Prodigy 20 points

Hi Timothy,

0 ELVIS SUN over 3 years ago in reply to ELVIS SUN

Prodigy 20 points

hi timothy, sorry for the several emply reply minutes ago. yes , i set the current limit up to over 28A it works well, however the the designed output current is 3.5A while current limit set was 5.5A around. there should not be such gap between design and experiment. and refer to the drv constant for several periods as shown before, i guess this caused by the abnormal drv from some reason i don't know so far , to raise the current limit may just cheat to not limit the large inductor current which is charged quite high for somehow long time.

0 Timothy Hegarty over 3 years ago in reply to ELVIS SUN

TI__Guru 61007 points

Hi Elvis,

If you suspect noise affecting the circuit, please send the PCB layout for review. in particular, the FB node is noise sensitive and the FB trace should be as short as possible (locate the FB resistors very close to the FB pin). Also, send on the completed quickstart file. What is the MOSFET part number? We need to ensure it is compatible with the controller's gate drive amplitude.

Regards,

Tim

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LM25085-Q1: LM25085-Q1