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championx
Joined: 28 Feb 2006
Posts: 151
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 Posted: Wed Jan 11, 2017 8:38 am |
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Same Crystals... same caps... i discovered something... it seems like the PLL doesn't work...
I tested the board, same xtal, same caps, NO PLL and it works.
So...
XTAL + PLL: does not work
INTERNAL + PLL: does not work
INTERNAL: works
XTAL: works
Could be some variation on the PLL config on this PIC batch?? I'm really lost... |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Jan 11, 2017 10:32 am |
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| championx wrote: | | I'm developing a board that has a PIC 24EP512GU810, and I'm testing the third version of the board... the previous versions works fine, but this one i can't make it run |
In this thread here, it's a board assembly issue. Wrong cap.
http://electronics.stackexchange.com/questions/51485/cant-run-pic24ep128mc206-at-rated-speed
| Quote: |
FINAL UPDATE: Turns out that the person doing the board layout put a 0.1
uF cap on VCAP without looking at the datasheet and I never caught it
either. I swapped that out with a 10 uF 16v low ESR (datasheet called for
4.7 uF or higher) and now I can run at 70 MIPS. |
Another comment from the same thread:
| Quote: | I had the same problem with the PLL which didn't not lock on the high
frequency from my external oscillator. My problem was the ESR of
capacitor on the VCAP input. It must be less to 1 ohm (see PIC24E
datasheet), and in my case the ESR was 4 ohm, and it was not running. |
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newguy
Joined: 24 Jun 2004
Posts: 1904
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| Posted: Wed Jan 11, 2017 11:12 am |
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Assembly issues are very common - as PCM has pointed out, look to the caps. Perhaps buy a few crystal capacitors that are "known good" and swap out the suspect ones presently on the board.
My first real job out of university was for a very major electronics giant (that coincidentally no longer exists). My first exposure to a "you're fired, get out" screw-up of monumental proportions was caused by some nameless purchaser in a completely different location substituting ordinary capacitors for special AgPt termination capacitors used on an MCM. The substitution was done years prior, and for years no one could diagnose why the reliability of those MCMs was so poor (first pass yields of ~30% in functional test). Until one day someone finally noticed that the caps weren't actually bonding to the MCM.... |
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championx
Joined: 28 Feb 2006
Posts: 151
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| Posted: Wed Jan 11, 2017 1:37 pm |
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well... FINALLY!!!!
The problem was the vddcore capacitor... i was using a 10uF ceramic capacitor... i changed it to a 10uF tantalum cap and VOILA!
Thanks all for your help! Thanks A LOT! |
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