Hi All,

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?

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.

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.

thanks Martijn

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We have discussed this here in the past:
http://thread.gmane.org/gmane.comp.hardware.texas-instruments.msp430.discuss/12686/focus730

M.

On Sun, Jun 18, 2006 at 01:11:14PM -0000, Martijn Broens wrote:
> Hi All,
>
> 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?
>
> 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.
>
> 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.
>
> thanks Martijn
>
> Start a New Thread

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/

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