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'EE: A dumb mistake.'
2007\01\19@233325 by Rich

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Hi guys:
I stupidly put 5 volts to a 3.3 volt part.  I missed it in the checking and the PCB is fabbed.  I thought of lifting the pin (can't cut the trace because it is an internal layer) and knocking down the voltage with a zener glue-on.  I hope the zener impedance will be low enough.  The part is an EEPROM.  Has anyone had any experience with this type of fix?  I will get new boards for production but I don't want to spring for another 300 bucks for a test board.  I confess to stupid things from time to time.

2007\01\19@234924 by Mark Rages

face picon face
On 1/19/07, Rich <spam_OUTrgrazia1TakeThisOuTspamrochester.rr.com> wrote:
> Hi guys:
> I stupidly put 5 volts to a 3.3 volt part.  I missed it in the checking and the PCB is fabbed.  I thought of lifting the pin (can't cut the trace because it is an internal layer) and knocking down the voltage with a zener glue-on.  I hope the zener impedance will be low enough.  The part is an EEPROM.  Has anyone had any experience with this type of fix?  I will get new boards for production but I don't want to spring for another 300 bucks for a test board.  I confess to stupid things from time to time.

It will probably work, but you'll need to add a 50K resistor to ground
to make a bit of current go through the zener.

Does the EEPROM have chip enable inputs that are fixed at 3.3V?  You
could leave Vcc disconnected and power through the protection diodes
on those inputs.  Not a long term solution, but it might get you by
until your next board rev.

Regards,
Mark
markrages@gmail
--
You think that it is a secret, but it never has been one.
 - fortune cookie

2007\01\20@002324 by Robert Rolf

picon face
Mark Rages wrote:
> On 1/19/07, Rich <.....rgrazia1KILLspamspam@spam@rochester.rr.com> wrote:
>
>>Hi guys:
>>I stupidly put 5 volts to a 3.3 volt part.  I missed it in the checking and the PCB is fabbed.  I thought of lifting the pin (can't cut the trace because it is an internal layer) and knocking down the voltage with a zener glue-on.  I hope the zener impedance will be low enough.  The part is an EEPROM.  Has anyone had any experience with this type of fix?  I will get new boards for production but I don't want to spring for another 300 bucks for a test board.  I confess to stupid things from time to time.
>
>
> It will probably work, but you'll need to add a 50K resistor to ground
> to make a bit of current go through the zener.
>
> Does the EEPROM have chip enable inputs that are fixed at 3.3V?  You
> could leave Vcc disconnected and power through the protection diodes
> on those inputs.  Not a long term solution, but it might get you by
> until your next board rev.

If you can lift the pin to put in a zener, why not just use a wire jumper
to 3.3V? Wire wrap wire works nicely for this.

R

2007\01\20@045210 by Vasile Surducan

face picon face
Lifting up the EEPROM VCC pin and connecting a 0402 SMD resistor
between the pin and the 5V circuit and a standard two terminals 3.3V
zenner between Vcc and GND of the EEprom's  SO package looks also
good.
It's not a big deal Rich, but the same amount of work (or less) will
be desoldering and replacing the part.

Vasile

On 1/20/07, Rich <rgrazia1spamKILLspamrochester.rr.com> wrote:
> Hi guys:
> I stupidly put 5 volts to a 3.3 volt part.  I missed it in the checking and the PCB is fabbed.  I thought of lifting the pin (can't cut the trace because it is an internal layer) and knocking down the voltage with a zener glue-on.  I hope the zener impedance will be low enough.  The part is an EEPROM.  Has anyone had any experience with this type of fix?  I will get new boards for production but I don't want to spring for another 300 bucks for a test board.  I confess to stupid things from time to time.
> -

2007\01\20@051435 by Rich

picon face
Yes, Mark.  The chip does have an CS NOT. It is held high (+5V now instead
of 3.3V) so I have to do something there also until I get the new boards. I
don't want to order new boards until I prove all circuits/timings etc on
this one. I thought of diodes in series on that pin.  Think that can work?



{Original Message removed}

2007\01\20@051946 by Rich

picon face
Thanks for the reply, Vasile. I hope a 5V pin compatible part is available.
That would sure make things easier.


{Original Message removed}

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