LMR33630: negative 12V-out can not work

Henry Wang3

Genius 3325 points

Part Number: LMR33630

Hi Sirs,

My customer is developing a board to use the LMR33630 for 5Vin to -12Vout and Iout 0.5A.

They found the -Vout pin can not generate the -12V, could you please help to check and advise the schematic?

Thanks for your support.

0 Frank De Stasi over 4 years ago

Hello

We cant read your schematic file. Please send a PDF.

Also send snapshots of your PCB layers

When you say it does not give -12Vout, can you be more specific?

Please send waveforms or the SW node and Vout node.

Did you use Webench to design the inverter?

Please see the attached sample Webench design and compare.

Please see attached app note for tips regarding IBB design.

Thanks

0 Henry Wang3 over 4 years ago in reply to Frank De Stasi

Genius 3325 points

Hi Sir,

The customer followed the attached webench file to do the design.

Please see the attached the customer's LM33630B schematics, layout, and waveforms of the SW node and V-out node.

+1 Frank De Stasi over 4 years ago in reply to Henry Wang3

Hello

I assume you are using the 400kHz option. You will need a larger inductor, such as the

10uH shown in the Webench design. Also, your output capacitors are rated for only 16v.

They will de-rate a great deal at 12Vout. You should try using 25-V rated capacitors.

How much load current were you using to take the scope shots?

The PCB layout seems OK.

Thanks

0 Henry Wang3 over 4 years ago in reply to Frank De Stasi

Genius 3325 points

Hi Sir,

This issue has be solved.

Thank you for your kind support.

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