LM3150: Excessive heat in Mosfets

Mike Farley

Part Number: LM3150
Other Parts Discussed in Thread: CSD17302Q5A

Dear Forum,

I have a customer who has 3 convertors on one power supply board (attached schematic) and has thermal management issues. Please see this link for the LM3150MH design that has been implemented:

https://webench.ti.com/appinfo/webench/scripts/SD2.cgi?ID=200214::power::mike.farley@ti.com

The input/output specs for the two identical LM3150 converters in the real design are less stringent than the Webench design, and are as follows:

Vin = 12V, Vout = 7.5V

1. At up to 4A load current in the first application

2. At up to 8A load current in a later application

Issue:

In case (1) above Tcase of M1&M2 CSD17302Q5A Mosfets on both convertors are above 90degC in application. (the whole board is hot indicating good heat sinking - the customer is collecting detailed thermal images at the moment)

Webench simulations say M1&M2 Tj should be around 40deg at 4A and rising to 50-60deg for 8A, and the LM3150 Tj is 38DegC across the loading.

-> Please review and advise. Waveforms and schematic attached.

Many thanks!

Mike

LM3150 Waveforms_pdf.pdf

over 7 years ago

0 Samuel Jaffe over 7 years ago

TI__Mastermind 25590 points

Mike,

I'm interested to see the detailed thermal images. It could be that everything else is well heatsinked which is heating up the board.

The WEBENCH link did not work for me. It says I have to be logged on as you to see it.

I can't find anything wrong with the schematic but I'm going to keep looking.

-Sam

0 Samuel Jaffe over 7 years ago in reply to Samuel Jaffe

TI__Mastermind 25590 points

Mike,

Are you using the tip-and-barrel method to get those waveforms? Namely the SW node. I want to make sure those peaks are really there because SW node looks like it peaks close to 30V. CSD17302Q5A is rated for VDS=30V. That could possibly damage the FETs and hurt performance which may lead to something like you're seeing.

-Sam

0 Mike Farley over 7 years ago in reply to Samuel Jaffe

TI__Prodigy 735 points

Thanks very much Sam.

I or Ram will pass along the thermals once we have. Ill have pass along the original customer link to your mail as it has the customer name in the link tomorrow.

Thanks?

Mike

0 Mike Farley over 7 years ago in reply to Samuel Jaffe

TI__Prodigy 735 points

Probably not scope tip and barrel and likely still with flying scope ground lead Sam, So dont read too much into that just yet.. but i will check..

Thanks - the thanks? below was a typo! :)
Mike

0 Samuel Jaffe over 7 years ago in reply to Mike Farley

TI__Mastermind 25590 points

That's what I figured? Get back to me :)

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LM3150: Excessive heat in Mosfets