LM5088: In case of short circuit, the mosfet and output capacities are burning.

Onur Keskin

Part Number: LM5088

Hi,

I am design a DC-DC converter. Now, i'm in the test phase. There is a problem with the short circuit test. I am using SQJ82EP mosfet. In case of short circuit, the mosfet and output capacities are burning. How can i solve this problem?

The specs of design;

Vin = 15-60 V

Vout=12 V Iout = 3 A (typ)

Mosfet = SQJA82EP N-Channel 80 V (D-S) 175 °C MOSFET

Diode = FSV10100V 10A 100V Ultra Low VF Schottky Rectifier

over 6 years ago

0 David Baba over 6 years ago

TI__Mastermind 39790 points

Hello Onur,

Please can you post schematic? Thanks.

David.

0 Onur Keskin over 6 years ago in reply to David Baba

Intellectual 390 points

Hello David,

I added the relevant part.

BR.

0 David Baba over 6 years ago in reply to Onur Keskin

TI__Mastermind 39790 points

Hello Onur,

what is the Isat Rating of L3? Needs to be greater than 9A according do you component section and specification.

Please confirm this is the case with L3?

Thanks.

David.

0 Onur Keskin over 6 years ago in reply to David Baba

Intellectual 390 points

Hi David,

I am using Würth 7443320820. Rated current 13A. As you said, I set the peak current to 9A. So the coil meets the specifications. I tested five times. Fet and capacitors in all short circuit tests burned.

Onur.

0 David Baba over 6 years ago in reply to Onur Keskin

TI__Mastermind 39790 points

Hello Onur,

Can you please provide the layout so I can check? Thanks.

David.

0 Onur Keskin over 6 years ago in reply to David Baba

Intellectual 390 points

Hello David,

I'm adding a schematic and layout.

0218.layout.pdf

4380.sch.pdf

0 David Baba over 6 years ago in reply to Onur Keskin

TI__Mastermind 39790 points

Hello Onur,

First thing I would try, is to add Rramp from the Cramp pin to Vcc. recommend Cramp = 330pF and Rramp = 350k

I checked your layout and I see an issue, Cin needs to be close to Top FET, Rectifying Diode and Rsense. Please see recommendations in the attached. This can certainly have an effect on functionality and reliability if not done correctly. You can perhaps try kludging CIN ceramic close to the Power components. As it is, CIN looks very far away. See attached floor plan recommendation for the LM5088.

lm5088 Floor Plan.pdf

Hope this helps?

David.

0 Onur Keskin over 6 years ago in reply to David Baba

Intellectual 390 points

Hello David,

Thanks your suggestion. I tried add Rramp and i changed Cramp. But this is not resolved my problem.

I will change my design and layout. I'll let you know when i tried with the new pcb.

BR,
Onur.

0 David Baba over 6 years ago in reply to Onur Keskin

TI__Mastermind 39790 points

Thanks Onur,

Please open a new thread if any issues arise in the future.

Thanks.

David.

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LM5088: In case of short circuit, the mosfet and output capacities are burning.