Re: tiny inductor with every bypass cap?

"Vladimir Vassilevsky" <antispam_bogus@[EMAIL PROTECTED]
> wrote in message 
news:8vA7k.5248$L_.3435@[EMAIL PROTECTED]
>
>
> 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

Hello Vlad,

We were able to arrange for calibration of the ADC on board and could
easily 
deal with the offset issues.

We went 4 layer because we wanted it to work first time, 6M samples/sec
and 
reasonable ADC performance for an on chip quite fast ADC.

It worked and was delivered on time and to spec.

Sure we could have got it on 2 layers, delivered it late, not quite
working 
and saved a few £ on the board.

Did you never hear of "good, cheap, quick - pick any two" ?

Michael Kellett