Dear Forum
I am still battling like the Spartan 300 on this to get this wonderful chip to work 'for me'... I've discovered some alarming issues that are intuitively suggesting I might have a problem with the test power supply grounding.
1) I've checked my PCB a million times. (no shorts and all connections are DRC checked. I ensured my schematic of the chip is accurate)
2) I noticed that ONE side of the 3255 came alive and functioned fine.
3) I checked the following pins "AVDD and DVDD" and found AVDD was occasionally 'there' and then not. The disturbing thing was, when I moved my finger close to the Reset line (but not touching) it would come ALIVE and be the correct voltage of around 7.5v... move my finger away.. dead. Other times it's up and down like a yoyo on/off... on.. etc. I cannot for the life of me see how AVDD would dissappear simply because of some capacitive closeness of my finger to the reset line. (yes, I've changed the chip a few times to eliminate possibilities)
4) The only thing I can come up with as to why this very inconsistent and erratic behavior is happening, might be related to my rather long DC power leads. I have 2 supply sources. +/-12 for the low voltage lines (the -12 is for my op amp) and 31v for PVDD.
5) I see on the EVM that you have tied both FAULT and CLIP to 3.3v via some resistors. (47k) But I understood from the Data sheet that these are internally tied to a pull up voltage. Is there a special reason for this connecting to 3.3v outside the chip?
I've got very good ground planes all over the board, so I don't think that's the problem...however the length of lead to my power supply is concerning me at last.
Could some one make an informed comment about whether this kind of erratic behavior could be likely coming from long ground lines to my power supplies? I can't see much different between my device and the knock off fake TI unit from China (which worked fine).. except that it uses a buck converter close to where the 53v comes in..and obviously, the grounding and supply lines are very tight compared to mine.
Looking for some answers....
Julian