Could be some sort of inrush current effect. Also, if there is a secondary
power supply downstream, it may require the input to have a fast risetime.
Especially if power supply sequencing is important.
Check that your crystal is operating OK.  Dust/dirt providing a leakage
path & preventing correct startup?
Another thing to check would be the reset/brownout arrangements - could be
on the edge?



RP.


On 24 June 2014 04:42, Robert Dvoracek <lgtngstk@hotmail.com> wrote:

> That's strange.  I would try swapping out caps, especially if they are
> electrolytics.  Old electrolytic capacitors can cause funny problems that
> are a bear to diagnose.  I try to stay away from aluminum and use ceramic
> or tantalum when at all possible.
>
> ----------------------------------------
> > From: jana1972@centrum.cz
> > To: piclist@mit.edu
> > Date: Mon, 23 Jun 2014 16:42:45 +0200
> > Subject: [EE] Asynchronous Step-Down Regulator problem
> >
> > I have a Linux embeded board that uses
> > FP6116 Asynchronous Step-Down Regulator
> > a datasheet is here
> > http://www.micro-bridge.com/data/Feeling-tech/FP6116.pdf
> >
> > In this design , that Asynchronous Step-Down Regulator should supply
> 1,2V for CPU on
> > this board.
> > It worked for some time but now it stopped.
> > So, I measured voltage and that Asynchronous Step-Down Regulator still
> supply 1.2V, yet
> > CPU does not start.
> > But when I use a different source of 1.2V, the CPU starts.
> > So, I am rather confused.
> > I can measure the same voltages, and more or less the same spikes( usin=
g
> oscilloscope), yet
> > different results.
> >
> > Can anyone suggest any solution to that problem?
> > Thanks
> > --
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