(Solved)  LPC-Link 2 Apparently burning out JTAG connections

Discussion created by lpcware Employee on Jun 15, 2016
Latest reply on Jun 18, 2016 by lpcware
Content originally posted in LPCWare by xenthan on Fri Apr 08 07:50:45 MST 2016
I have had 4 chips simply stop being recognized by the debugger (both JTAG and SWD).  I've done 3 different designs now using the LPC4357 (both quad flat and BGA) and the LPC4337.  They have all been programmed using LPCXpresso and I have used 3 different LPC-Link 2  debuggers.  After maybe 3-5 days of programming (4-5 hours per day), the device simply stops being recognized and I am no longer able to program the chip.  I've tested the debugger on another board and it still functions fine.  The program maintains its last state (LEDs blinking, other ICs on the board being initialized and functioning), so the processor itself isn't getting scorched.  Power is supplied via a separate LDO and a wall wart, so I'm not pulling too much current through the  header.  I have a 10k pull-down on the TCK pin and everything else is pulled up internally (except for the TDO line), so I don't believe that's the issue.  ISP pins aren't broken out so I can't check things that way (lesson learned). 

My boards pull a little over 1A total, so maybe there's some issues there when the LPC-Link is attached?  The only connection to my computer's ground is through the LPC-Link's USB port, but I would think that excessive current through that would affect the debugger, not the board itself.  Any ideas?

Further testing is showing that the TDI pin seems to be damaged (800 ohms to VDD, 300 to GND) on each board.  Seeing as this is a dedicated input, I'm leaning more and more towards something strange happen with the LPC-Link2.

I believe the problem is that there is an issue with using the LPC-Link2 as the sole ground to the PC.  I'm not sure why the LPC43xx chips are the ones that get burned out and not the programmer, but after adding a second ground via a USB cable, the problem has gone away.  I'm pretty sure the potential between the AC/DC converter ground and the PC ground was causing an inrush of some kind that was blowing up the chips.  Still not sure why the LPC-LINK2 is still functioning (would rather have the programmer burn out, not the processor), but I can work around that.  The "Logic Levels and Ground" section of  https://www.lpcware.com/content/faq/lpcxpresso/debug-design hints that the ground could be the issue, but there's no mention of it burning up the actual target board.