AVR-Chat

David VanHorn wrote:
>>> If there isn't enough load to pull that current back out of the rail,
>> you
>>> end up raising the 3.3V rail out of spec.
>> Latchup only happens over a certain thresh-hold, so if you're confident
>> that your overdrive is always much lower than that, then problem solved.
> 
> I'm not willing to generalize the behaviour of an unpublished parameter
> across large numbers of chips from a small sample, especially when the
> variability of that parameter is unknown.

You only try it on unpublished data when fixing stuff-ups.

> Also, what do you do about the current you're dumping into the 3V system?

It feeds the 3V power supply.

> I saw something like this happen on a 5V system where the incoming current
> was enough to shut down the output of the 5V regulator, and raise VCC to
> 5.24V.  While this SEEMED to be barely within tolerance, the systems
> suffered from unpredictable crashes.  Eliminating the source of the excess
> current into VCC solved the problem.
> In this case, the current into VCC was coming through the protection diodes
> on a ULN2003, which are rated for some fair current, and the problems were
> not latchup related.