> It's a 5 ohm motor, bipolar windings, running from a 6-8.5V supply.
> The motor wants 0.5A. I don't want to spend any more power than I must
> in driving it, since this is a battery operated application.

You can't afford the losses of a darlington output device so your
best solution is probably to go semi-discrete with N-ch/P-ch half
bridge drivers or perhaps a low voltage DC motor driver device. Then
add your own current sense/chopper circuit.

I'd be tempted to have a play with MOS output controller IC's you've
already dismissed because of the minimum motor voltage.
AFAICT, the minimum would be dictated by the ability of the
charge pump to get a high enough Vgs on the top FET to turn it
hard on. I would expect that with a 6V supply you're going to be
close enough that even if the Rds on is twice what it is capable of,
you are still on the winning side. Try it. If it works OK for your
needs, flick an email to the chip supplier and ask for their opinion.

Steve.

======================================================
Steve Baldwin                Electronic Product Design
TLA Microsystems Ltd         Microcontroller Specialists
PO Box 15-680, New Lynn      http://www.tla.co.nz
Auckland, New Zealand        ph  +64 9 820-2221
email: steveb@tla.co.nz      fax +64 9 820-1929
======================================================

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