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lpc2106 Overheating

Started by ds19968902 January 25, 2005

I recently posted about sourcing the lpc2106 due to burning a few of
them lately. Leon Heller asked as to how they got fried so I put some
information together. Now this has occured with the lpc2106 board
from olimex, both the 40pin header and proto board. Im using
Crossworks.

The wiggler-compatible JTAG connector (Olimex) seems to be causing
sporadic mishaps, which in turn fry the LPC2106. The normal 3.3V
supply current to the JTAG connector itself is around .7mA, going as
high as 1.7mA when downloading a program to the '2106. When the fault
condition is present, however, the supply current increases to 37mA.
I set up the JTAG connector to be supplied by by a sourcing-only
power supply (op-amp with a transistor instead of pulling a wire from
the headerboard since I thought it was sloppy to wire to the supply
on the 40-pin header), and it appears as though the 3.3V supply
current is being sent from the supply through the JTAG connector, to
the LPC2106 straight to ground, since the supply's transistor always
becomes hot when the '2106 becomes hot. The only way the 3.3V supply
and the '2106 are connected is through the JTAG connector. I am
speculating that an output on the JTAG connector is trying to pull a
pin high that leads to the '2106, which in turn is trying to pull
that same pin to ground. I suspect that this might be a flaw in the
JTAG connector itself, since nothing but the JTAG is connected to the
processor. I don't know which pin on the JTAG cable might be at fault
here, and I cannot reliably produce the fault condition that fries
these chips. On occasion, some action on the software side, such as
disconnecting or processor reset causes the fault to occur.

I greatly appreciate any ideas or comments on this issue.
Thank You!
Eric




An Engineer's Guide to the LPC2100 Series

----- Original Message -----
From: "ds19968902" <>
To: <>
Sent: Tuesday, January 25, 2005 4:15 AM
Subject: [lpc2000] lpc2106 Overheating >
>
> I recently posted about sourcing the lpc2106 due to burning a few of
> them lately. Leon Heller asked as to how they got fried so I put some
> information together. Now this has occured with the lpc2106 board
> from olimex, both the 40pin header and proto board. Im using
> Crossworks.
>
> The wiggler-compatible JTAG connector (Olimex) seems to be causing
> sporadic mishaps, which in turn fry the LPC2106. The normal 3.3V
> supply current to the JTAG connector itself is around .7mA, going as
> high as 1.7mA when downloading a program to the '2106. When the fault
> condition is present, however, the supply current increases to 37mA.
> I set up the JTAG connector to be supplied by by a sourcing-only
> power supply (op-amp with a transistor instead of pulling a wire from
> the headerboard since I thought it was sloppy to wire to the supply
> on the 40-pin header), and it appears as though the 3.3V supply
> current is being sent from the supply through the JTAG connector, to
> the LPC2106 straight to ground, since the supply's transistor always
> becomes hot when the '2106 becomes hot. The only way the 3.3V supply
> and the '2106 are connected is through the JTAG connector. I am
> speculating that an output on the JTAG connector is trying to pull a
> pin high that leads to the '2106, which in turn is trying to pull
> that same pin to ground. I suspect that this might be a flaw in the
> JTAG connector itself, since nothing but the JTAG is connected to the
> processor. I don't know which pin on the JTAG cable might be at fault
> here, and I cannot reliably produce the fault condition that fries
> these chips. On occasion, some action on the software side, such as
> disconnecting or processor reset causes the fault to occu

It sounds like they are going into 'latchup', the device behaves like an SCR
and draws *lots* of current. It used to happen sometimes with the Inmos
transputer if one touched the top of the device whilst it was powered up.
The metal lid wasn't grounded and static could initiate the condition. They
always recovered if the power was removed. I've occasionally had it happen
with other devices, but it's quite rare these days, with modern CMOS.

ADI has a good description of the phenomenon and how to avoid it:

http://www.analog.com/library/analogDialogue/archives/35-05/latchup/

Leon
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