Re: Need power supply rework ideas for PLL
- From: "Paul Hovnanian P.E." <paul@xxxxxxxxxxxxx>
- Date: Thu, 14 Dec 2006 12:40:22 -0800
Ben Jackson wrote:
I'm trying to fix a clock problem on a freebie board I got. It drives
an expensive display, so it's worth fixing. It appears to be a 4-layer
board with signals on the outside and +5/GND inside. +5 comes from a
header along one edge that connects to a fairly long wire back to a SMPS.
There's a CY7B992 programmable skew clock buffer in PC32 (datasheet link
below) on the board in one corner. It's powered by the +5V plane. When
the embedded PC that connects to this board works hard, the clock out
of that chip has problems which manifest as display glitches. I suspect
that the 5V quality is not up to snuff near that clock buffer (I had
assumed it was powered by the adjacent 3.3V regulator when I first
examined the board, but it's not).
On first impression, it might be that "long wire" back to the supply.
Throw an o'scope on the 5V header, run the board through its paces and
look for glitches.
What kind of I/O runs from the embedded PC and this board? How is it
powered and grounded? Put the 'scope between the PC and board grounds
and look for noise.
--
Paul Hovnanian mailto:Paul@xxxxxxxxxxxxx
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