LM25145DESIGN-CALC: LM25145

John Man

Part Number: LM25145DESIGN-CALC
Other Parts Discussed in Thread: LM25145

Dear Sir,

I am currently using LM25145 to design a buck circuit for a circuit board. When I do design verification, I found the EN/UVLO function has some issue. I used 100kohm as RUV1 and 24.9kohm as RUV2 to set turn on voltage of 6V and turn off voltage of 5V.

The turn off threshold is good, When I decreased the input voltage to 5V, the regulator ceased switching. However, when I increased the input voltage higher than 6V(even to 12V), this regulator refused to be restored. I did the test with constant current load of 2A, 1A and 0.5A. Neither one can make it recovered.

Can you help to check this issue?

Thanks

John

over 1 year ago

0 Timothy Hegarty over 1 year ago

TI__Mastermind 49397 points

Hi John,

Please send the schematic and completed quickstart file. Check if it starts up with EN/UVLO tied to VIN. Note there is also a VCC UVLO threshold.

Regards,

Tim

0 John Man over 1 year ago in reply to Timothy Hegarty

Prodigy 20 points

Hello Tim,

EN/UVLO is not tied to VIN, instead, it connects to VIN through 100kohm resistor and connects to GND through 24.9Kohm so as to achieve turn on/off function. There is no tool box that I can insert the schematic to this response box.

Thanks

John

0 Timothy Hegarty over 1 year ago in reply to John Man

TI__Mastermind 49397 points

Hi John, you should be able to attach the files here. Also, try connecting EN/UVLO to VIN to bypass the turn on/off function and see if the behavior persists.

Regards,

Tim

0 John Man over 1 year ago in reply to Timothy Hegarty

Prodigy 20 points

6567.Schematic Prints.pdf

Hi Tim,

If the CC load is changed to 0A, then the regulator can be recovered without the need of attaching EN/UVLO to VIN. The schematic is attached.

Thanks

John

0 Timothy Hegarty over 1 year ago in reply to John Man

TI__Mastermind 49397 points

Thanks, John. Just looking at the schematic, 4.7uF isn't much for ceramic input cap. Try 1-2 pcs of 10uF/50V or 22uF/25V instead. The 100uF electrolytic is just for input filter damping and doesn't reduce the input ripple. You can also use a small cap on EN if noise is present.

PS: we have converters (with integrated FETs) for 4A load - easier implementation.

Regards,

Tim

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LM25145DESIGN-CALC: LM25145