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LM3478: PCB has been made and the circuit isn't working

BonJae Koo

Prodigy 65 points

Part Number: LM3478

Dear TI Community,

I am having a trouble with the circuit so i'm trying to get a help here.

I made output of 10V/1A circuit using LM3478 as below which I designed based on WEBENCH tool.

The PCB has been made and I soldered all the parts. The problem is now, it seems like the circuit is shorted and I can't figure out why. I soldered components muliple times with different PCB so I am sure soldering skill isn't the issue here.

Please take a look at the schematic and give me any suggestions. Any help will be appreciated. It has been days I worked on this problem and I could't figure out so...

Thank you for your help!

over 5 years ago

0 Garrett Roecker over 5 years ago

TI__Mastermind 21720 points

Hi BonJae,

Thanks for reaching out and for using the LM3478.

Is the MOSFET getting hot? My guess is that the MOSFET is getting shorted. Can you post a picture of the layout? The schematic looks okay.

Also what is the value of the output capacitor?

Thanks,

Garrett

0 BonJae Koo over 5 years ago in reply to Garrett Roecker

Prodigy 65 points

hanks for your help Garret.

MOSFET is not getting hot but L1 is getting hot.

Output capacitor value is 47uF. I assume that not having the bypass resistor before Vin(pin 8) can cause this problem?

0 Garrett Roecker over 5 years ago in reply to BonJae Koo

TI__Mastermind 21720 points

Hi BonJae,

I don't think the VIN bypass resistor and capacitor are the issue.

With output power applied please see if the MOSFET is damaged. This is typically the part that will cause the input voltage to be shorted.

Thanks,

Garrett

0 Youhao Xi over 5 years ago in reply to Garrett Roecker

TI__Guru* 78270 points

Can we assume the issue is resolved? Lets close the thread here, and you are welcome to reopen it by adding a new post.

Thanks,

Youhao Xi, Applications Engineering