> will be never a better H bridge than let say BA6209 from Rohm,
> KA3100D
from Fairchild, 2xMC1472 from Motorola, LB1838 from who knows and
maybe another dozens of specialised IC for H or H/2 bridge.
/>

1.    Price is a major factor. So far most integrated bridges that I
have seen are far dearer than a discrete solution.

2.    Voltage limiting and also the ability to start at high current
are desired. Integrated bridges may not (but may) address this need.

3.    Best performance at low battery is needed. There may be some
cheap integrated bridges that allow this but some which were referred
to previously were terrible in this respect.

The specification SEEMS trivial but is more demanding than may at
first appear.

Let's look at the first IC on your list as an example:
BA6209 ROHM.
Digikey $US0.60/600 so maybe $US0.30/1000 in Taiwan.
ROHM disown it :-)
After an amazingly annoying search ...

Minimum operating voltage = 6 volts :-(
(That's the logic section - power sectioncan go lower BUT I don't have 
6 volts guaranteed).
Idle current (which I failed to mention this time but its in the old 
details) which needs to be ~~~= 0 is 5 mA ;-(
Saturation voltages appear higher than desirable.
And more :-(.
I don't know if it addresses max voltage drive.

I'm NOT suggesting that one of the above won't work
Just that it's a less than trivial requirement.


KA3100D - looks better.
Quiescent current needs addressing somehow.

LB1838
Looks good
Quiescent?

Don't know about cost for these but should be good due to volume 
markets they are used in.

______

> The weak point of this design is the RL amortizing circuit (22 ohm 
> in
parallel with the motor, because it's sourcing current from the
batteries when it should not).
Thar 22 ohm resistor may be connected in a different way with just one
transistor which will be ON only when the H command stops. I let the
lighty brains from this list to show the way, even I know you already
see it.
/>

It doesn't help BUT it's probably not the main problem.
Two back to back MOSFETS in series would remove it when the motor was 
running. As motor is bidirectional, using bipolars is less easy but 
can be done.

Thanks for the thoughts.


            Russell


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