[sdiy] DAC/REF Data sheet / Dev board R question

[Neil Johnson]

Hi Justin,

> http://www.sdiy.org/juz/REF_DAC_01.png
>
> C11 has a 1R5 R between it and ground.
>
> Can anyone suggest what purpose that R might be serving?

If you read the REF5025 datasheet (yeah, I know, who bothers reading
datasheets on a Saturday afternoon, eh?) you'll find this text:

"A 1-μF to 50-μF, low-ESR output capacitor (CL) must be connected from
VOUT to GND. The ESR value should be less than or equal to 1.5 Ω. The
ESR minimizes gain peaking of the internal 1.2-V reference and thus
reduces noise at the VOUT pin."

Since we can reasonably assume that the folks who wrote the document
knew what they're talking about, or at the very least had access to
the folks who designed the chips in the first place, I think it wise
to carefully study the example circuit, since it would have been
designed to demonstrate the parts at their best (that evaluation
module is a marketing tool, so it needs to do battle with devices from
competitors).

Neil
--
http://www.njohnson.co.uk