A fancy way (but is not always true) I'm often use for unknown tantal SMD
is: the bigger SMD package (for the same capacitor value) has usualy
the lowest ESR value. LM2940 never gaves me problems.
Try:
http://pdfcatalog.digikey.com/T072/SectF.pdf
Do a search in the pdf with "low ESR" keyword. See what is matching
with your capacitor aspect.

Vasile

On 5/17/07, wouter van ooijen <wouter@voti.nl> wrote:
> I have always used the 7805 types, but now I need a lower drop
> regulator. Both the LM1117 and the LM2940 pose requirements on the
> output cap. For the LM1117 the ESR must be 0.3 - 22 Ohm, for the LM2940
> 0.1 - 1 Ohm. I mostly use generic (no specific manufacturer) components,
> so I can't check their datasheets. So: what are typical ESR values for
> off-the-shelve elco's (and if they are not likely to meet such
> requireents, of tantaliums)?
>
> Wouter van Ooijen
>
> -- -------------------------------------------
> Van Ooijen Technische Informatica: www.voti.nl
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> docent Hogeschool van Utrecht: www.voti.nl/hvu
>
>
>
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