Lpc2000

Random guess.  Power supply sequencing and SCR latchup internal to the
part.  Does the problem occur is both supplies are discharged to ground?

"POSSIBLE" solution, i.e. untried guess.  Backbias a schotty diode across
3.3v and 1.8v supplies so the 3.3v supply will never go below the 1.8v
supply.  No guarantees, but something to try.


Regards
-Bill Knight
R O SoftWare



On Wed, 25 Feb 2004 07:31:31 -0000, tsvetanusunov wrote:

Hello,
This is a message which I posted last Friday on Philips 
microcontroller forum. It seems that nobody from Philips is reading 
this forum though as the only one who responded was Leon who observed 
the same problem to one of his boards too, so I cross post here with 
hope that somebody with more information/experience on LPC2106 would 
help:

----QUOTE---
Hi everybody, 

We have designed few development boards for LPC2106. 
The schematics are posted at http://www.olimex.com/dev 
Now we are running lot of 250 pcs LPC-P1 boards and experience the 
following problem: if we program simple blinking led program into 
LPC2106 flash and then disconnect and re-connect power supply in 
random timely manner on 10 % of the boards sometimes LED doesn't 
start to blink i.e. program is not executing, but after several 
plug/unplugs LED start to blink. 
In both cases i.e. program run or program doesn't run oscillator is 
working with same frequency and amplitude i.e. it's not oscillator 
powerup problem. 
It's not reset problem also as even if we hold reset button while 
plug/unplug and release reset button after power supply is stabilized 
i.e. 1 second the code still may not run. 
The power supply is adjusted to be exactly 3.3V with 1% resistors on 
LM1117. 
An interesting thing happens if we decrease input power supply (by 
adding the Z diode i.e. disconnect Z_J jumper) in this case LM1117 
have no enough Vin to make 3.3V and decrease output to 2.5V but here 
is the interesting part: all boards which run the code in randomly 
manner now are working each time if the Vcc is 2.5V! 
As I wrote above this happend to only 10% of the boards all other 90% 
works solid no matter what power supply is. 
I looked desperately on Philips LPC2106 web for technical support 
link to report this issue but there apparently have not such, so I 
decided to post this here in the forum. 

So any ideas? 

Best regards 
Tsvetan
---END QUOTE---





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