AVR-Chat

1. Be sure to read  the data sheet for the regulators.  I just 
redesigned my board and chose to use a national semi LDO which does 
not like MLC caps.  I happen to also like MLC caps as generally they 
work great.

I also had a heavy load which i found drooped my input source enough 
that my switching regulator would also droop 20 millivots. So what i 
did was put the heavy load on  the 12VDC incomming supply and I 
used  the LDO regulator to regulate that 12VDC down to 10.2 and  
then on to my switcher which generatest the +/-5 and 3.2VDC.  Now my 
analog and AVR will not see the droop.

I also recommend ferrite beads on  the incomming power and ground 
lines.  I found this helps with EMC filtering.

Al Welch

--- In AVR-Chat@yahoogroups.com, "Mike Murphree" <mike@t...> wrote:
> Jim Wagner said:
> >
> > Tantalum caps are nice because of small size and low ESR.
> > ESR isn't much of a requirement in linear regulators. But,
> > they cost more, have limited voltages and values, and have
> > a tendancy to destroy themselves (ie, explode or burst into
> > flames) if not in a current-limited circuit. Thus, putting
> > them in a place where they directly "see" battery power is
> > asking for trouble. It is less of an issue on the output
> > since the regulator, itself, provides current limiting.
> > They also tend to be more attractive on the output side
> > since the larger value is needed there. A general rule
> > commonly used by designers is to specify a tantalum voltage
> > rating that is about 2X the actual working voltage.
> 
> We have typically used MLC (multilayer ceramics) on switching 
supplies
> with some additional electrolytics if needed for bulk 
capacitance.  The
> MLC capacitors have an extremely low ESR and can be more effective 
than
> tantalum capacitors.  Also ceramic capacitors are more tolerant of 
applied
> voltages and are often tested to 4X or more of rated value at the 
factory.
> 
> Mike