Hello Martijn,
>
> i was wondering if anyone could point me to some appnotes on how to
> use an msp as a dc/dc stepup converter?
>
> For an automotive application i'm looking into, i need an mcu to
> swich some i/o and to flash some high bright LED's (700mA, 6.8V)
> there fore i need to boost my main voltage from 8V < Vin <= 13.8V to
> approx 21V (3x 6.8V). and i was wondering wether i could do this
> with the same msp?
>
Why not? See the thread Matthias pointed out.
TI's code examples and many app notes are IMHO a bit on the shallow
side but you could look at Microchip's AN-216 to see how it's done.
Beware of some pitfalls:
The 3.3V of an MSP430 has a hard time driving any FETs. You might need
a BJT or spend a little more on the FETs. "Spending a little more" can
be a problem in automotive apps. So if that isn't in the cards or you
find that your MSP is too maxed out for the high priority interrupt
routine that this DC/DC conversion requires consider other alternatives.
If it has to be off chip and the usual PWM controllers are too
expensive you could consider the CD4000 series since 8V-14V is just
the right range here. It's cheaper than PWM chips, usually.
Mind the right-half-plane zero (RHP zero) that can become a huge issue
in continuous current mode. Sometimes it's best to stay away from
that. The feedback loop is not trivial in a RHP zero situation.
> i found an old appnote in a book where they are using
an msp as
> boost converter but they don't describe how this is done and where
> the pitfalls are.
>
The USB-FET has one in there AFAIR. Probably a very simple pulse
skipping scheme.
> Has anyone ever done this? what er the possibilities
or should i
> stop this action and start looking for a cots part?? already done
> some research there but i was unable to find more than oine supplier
> and it needs to be small.
>
One supplier? Look at National, ON Semi and TI. They've got lots of
tiny switcher chips. Also, how small is "small"?
Regards, Joerg
http://www.analogconsultants.com/