Re: tiny inductor with every bypass cap?

MK wrote:

> I designed a board with an 'F2808 about 2 years ago.  Based on TI app
notes I
> put 100nH in series with the two ADC power pins only and 2uF to ground
on 
> each (2 * 0603 caps - different values).
> 
> Was it necessary - I don't know - never tried it without.
> 
> Did the ADC work - yes - I was impressed at how well it worked.

The internal ADC of TI 28xx is crap. It has tremendously inacurate 
internal reference and high zero offset. With 12 bits available, the 
true accuracy is about 8 bits unless you have the ADC calibrated.

> The board was 4 layers with careful design of gorund planes/fills around
the 
> processor and decoupling caps on both sides.

There is no need for 4 layer board with 28xx. The layout can be done on 
two layers just fine. Been there, done that.


Vladimir Vassilevsky
DSP and Mixed Signal Design Consultant
http://www.abvolt.com