Lpc2000

I'm working on a design that uses a LPC2106, but the design will be
migrating to the LPC2138 on the next revision of the PCB.

The LPC2106 seems to have difficulty starting (code does not seem to 
be executed) when the power supply slew rate exceeds a certain 
rate.  I don't yet have detailed measurements as I just stumbled 
across this in the lab.  

I will post the numbers after I do some careful measurements of the 
3.3 and 1.8 volt slew rates.  If I can determine what the CPU is 
doing via the JTAG interface, I will share that too.

Certain FPGAs are notorious for sensitivity to power supply slew 
rates. Power slew rates can be too fast as well as too slow.  A 
precedent for this weird behavior does exist.  Hopefully, I'm being 
mislead by something else or have just lost my mind entirely.

RESET is asserted for 200 ms after the power supply voltages are 
stable, then released.  The PCB is 12 layer, controlled impedance 
design with a great deal of bypassing and filtering.

Has anybody else observed this kind of LPC2106 behavior?

Thanks,
Wayne

Hi Wayne,

> RESET is asserted for 200 ms after the power supply voltages are
> stable, then released.  The PCB is 12 layer, controlled impedance
> design with a great deal of bypassing and filtering.

If RESET is really held low for that time, then the slew rate shouldn't
matter
AFAIK. Are you sure nRST and nTRST are sound ?
Boot pin ? Held properly while RESET is de-asserted ?
This might result in erratic entry into bootloader etc.

B rgds
Kris

Kris
 
Yes, all of those things you mentioned have been checked.  They work fine with the certain lower output current power supplies.
 
The only thing that looks different is the slew rate.
 
Thanks for your suggestions
 
Wayne

microbit <microbit@...> wrote:
Hi Wayne,

> RESET is asserted for 200 ms after the power supply voltages are
> stable, then released.  The PCB is 12 layer, controlled impedance
> design with a great deal of bypassing and filtering.

If RESET is really held low for that time, then the slew rate shouldn't
matter
AFAIK. Are you sure nRST and nTRST are sound ?
Boot pin ? Held properly while RESET is de-asserted ?
This might result in erratic entry into bootloader etc.

B rgds
Kris


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--- In lpc2000@yahoogroups.com, "dharmaBum" <dharmabum@y...> wrote:
> 
> I'm working on a design that uses a LPC2106, but the design will be
> migrating to the LPC2138 on the next revision of the PCB.
> 
> The LPC2106 seems to have difficulty starting (code does not seem 
to 
> be executed) when the power supply slew rate exceeds a certain 
> rate.  I don't yet have detailed measurements as I just stumbled 
> across this in the lab.  
> 
> I will post the numbers after I do some careful measurements of the 
> 3.3 and 1.8 volt slew rates.  If I can determine what the CPU is 
> doing via the JTAG interface, I will share that too.
> 
check the LPC2106 revision, if it's REV.B search the messages for the 
latchup problem with LPC2106

Best regards
Tsvetan
---
PCB prototypes for $26 at http://run.to/pcb 
(http://www.olimex.com/pcb)
PCB any volume assembly (http://www.olimex.com/pcb/protoa.html)
Development boards for ARM, AVR, PIC, MAXQ2000 and MSP430  
(http://www.olimex.com/dev)

Tsvetan
 
Thanks for the insight and yes, these are rev B parts on my board.  I will search the list
for "latch up".
 
Thanks again,
Wayne

tsvetanusunov <tusunov@...> wrote:

--- In lpc2000@yahoogroups.com, "dharmaBum" <dharmabum@y...> wrote:
> 
> I'm working on a design that uses a LPC2106, but the design will be
> migrating to the LPC2138 on the next revision of the PCB.
> 
> The LPC2106 seems to have difficulty starting (code does not seem 
to 
> be executed) when the power supply slew rate exceeds a certain 
> rate.  I don't yet have detailed measurements as I just stumbled 
> across this in the lab.  
> 
> I will post the numbers after I do some careful measurements of the 
> 3.3 and 1.8 volt slew rates.  If I can determine what the CPU is 
> doing via the JTAG interface, I will share that too.
> 
check the LPC2106 revision, if it's REV.B search the messages for the 
latchup problem with LPC2106

Best regards
Tsvetan
---
PCB prototypes for $26 at http://run.to/pcb 
(http://www.olimex.com/pcb)
PCB any volume assembly (http://www.olimex.com/pcb/protoa.html)
Development boards for ARM, AVR, PIC, MAXQ2000 and MSP430  
(http://www.olimex.com/dev)





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