LM43603: Question about odd via and drill hole structure

Carolus Andrews

Part Number: LM43603

Team,

Can you explain the purpose of the vias and drill holes surrounding the inductor in the EVM?

The top row look like vias as you follow it through the board to the bottom but the other rows don't seem to be anything other drill holes.

I've seen via stitching done in the past on nodes such as this, but I'm unfamiliar with what is happening here.

over 5 years ago

0 JohnTucker over 5 years ago

TI__Guru**** 191445 points

Carolus,

Those layouts look like they come from Webench. On the real EVM those upper vias are connected to an additional Vout copper pour area on the bottom layer.

0 Carolus Andrews over 5 years ago in reply to JohnTucker

TI__Mastermind 18780 points

John,

Understood. So the vias are for heat dissipation. Any idea on the drill holes?

0 David Baba over 5 years ago

TI__Mastermind 26520 points

Hello Carolus,

The vias are there to connect Vout and Gnd to other polygon pours on different layers in the PCB stack. Multiple vias are used to connect electrically and thermally.

Hope this helps?

0 Carolus Andrews over 5 years ago in reply to David Baba

TI__Mastermind 18780 points

David,

I get how vias work. The problem here was based on the customer's original description of the issue, and I thought these were actual drill holes in the PCB (i.e., no interconnection of planes), not vias. I am still curious, however, as to why we chose to thermally stitch in this linear fashion rather than over the totality of the plane.

0 JohnTucker over 5 years ago in reply to Carolus Andrews

TI__Guru**** 191445 points

Carolus,

They are not really thermal vias. The intent is to add extra copper to the Vout path to minimize conduction losses to the output connector. The placement is likely personal preference. I typically lay mine out either linear or in two row groups of 4 or 6 vias at each end of each output capacitor depending on the footprint size.

0 Carolus Andrews over 5 years ago in reply to JohnTucker

TI__Mastermind 18780 points

John,

This is exactly what I needed. Thanks!

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LM43603: Question about odd via and drill hole structure