On Tue, 19 Feb 2008 11:09:43 -0800, "Joel Koltner"
wrote:

This is the first cut of the production department's layout for this switcher.
I saw "first cut" because IMO it needs some serious adjustment -- with the
most obvious problem being the distance between L3 and C87. This is an
8-layer board (don't ask), and both ground and the output of the switcher
("Vcore") go to their own dedicated planes whereas the switcher's input
("VBAT") is a larger copper pour on another layer. (I've turned off the
layers other than the top as none of the switcher's nets are routed on them
and they make for a considerably messier plot... C28 and C30 are decoupling
the power pins on a connector that's on the bottom side of the board, if
anyone's curious.)

Critiques are always welcome!

---Joel

Boy, this breaks all the rules for switcher layout! Normally, you have
copper pours on the same surface as your controller IC to the various
high-current handling parts (C86, C87, L3, U11). Vias connecting the
nasty parts to a general plane are a really bad idea. Poor pin-4 may
be very unhappy with C86 and R29 connected the way they are. One of my
colleagues did this sort of layout and had a really hard time getting
the switcher to behave. A wire jumper between two ground plane
connected component terminals cleared up the issues (probably the
equivalent of U11-4 and the ground terminal of C86).

---
Mark