Joel Koltner wrote:
For those of you who read the "slightly misbehaving switchers" thread (which
has long since scrolled off my news server), I've had the chance to take a
look at the behavior of the switcher in question now that it's on an 8-layer
board with a ground plane. I've attached the results in the same format as
the original document. The Reader's Digest version of the results seems to
be... "nothing much has changed" -- there's still noticeable jitter in the
duty cycle with input voltages around 3V.

In any case, since the original (2-layer PCB) ended up working OK, I'm not
particularly worried about this (even though I wish the jitter weren't there
and don't really understand what causes it), I just wanted to share the
results with everyone helped on with the original problem.


Certainly doesn't look normal. Did you ever contact LTC about it?

I am not a particular fan of PWM chips with integrated power devices.
But in step-down converters it mostly works. With stepper motor drivers
that's a whole 'nother matter goose bumps, neck hair goes up.

C86 is a bit sub-optimal, should be between inductor and chip so it's
closer to pin 6. I assume GND is a full plane. If +VBAT is at least a
partial plane you could via pin 6 to it right near the pad, like you did
with pin 4. That change should be quite painless.

--
Regards, Joerg

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