Need more current from Allegro 3952 to drive 3V/1A motor

I'm trying to use an Allegro 3952 as part of a circuit that will drive a robot motor at 3v (4.5v max) at 1Amp max. I've followed the 3952
datasheet info and the circuit works...but not enough amperage seems to be coming out of the circuit to drive the motor.
I tried Vbb at 6V and 5V, Vref/Vcc at 5V, have an RC circuit, and have a sensing resistor (tried 0.5 ohms). With Vbb at 5V, the difference between OUTa when high and ground is 4.4v and -4.4v for OUTb. The difference between OYa and OUTb when one is high is 3.8v. A small amount of current (about 0.15A) seems to trickle through to move the motors a bit when I apply OUTa and GND to the terminals of the motor....but not much. Almost no current trickles out when I apply OUTa and OUTb to the terminals of the motor.
I'd ideally like to tie OUTa and OUTb to the terminals of the motor in order to control the direction of the motor.
Gordon McComb's robot book mentions the 3952 as a decent candidate for an H-bridge but I seem to be missing something (Gordon...if you're out there and have a suggestion...it will be appreciated).
Thanks in advance for any input!
Regards,
Paul
/******************************************************************/ Paul J. Perrone Assured Technologies, Inc. Web: www.assuredtech.com Author of various books on J2EE, Java, XML, and Web Services: http://www.assuredtech.com/books_page.htm Recently completed project includes the "J2EE Developer's Handbook" geared for J2EE v1.4. /******************************************************************/
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I basically built the sample circuit in the 3952 data sheet, and didn't have any significant problems. It wasn't a low-voltage motor, though. I used a 12 volt motor, and the logic voltage was 5V. I do know that most bridges don't like the motor voltage to be less than the logic voltage, and in some cases, it needs a volt or more overhead. I am unsure if this is the case with the 3952--it's been a few years.
For a 3V motor, you may need to use a low duty cycle, and a higher motor voltage.
I played around with the RC values to work with the motor I had. It was also useful to play with the Solutions Cubed Motor Mind B board -- which is still sold, and as far as I know, still uses the surface mount version of this chip. Their serial protocol makes it fairly easy to test different PWM settings. The cheap motors may not work at anything below about 60% duty cycle.
By design, pins 10 and 15 (OUTa and OUTb) are supposed to be connected to the terminals of the motor, so there should be no reason to tie one side of the motor to ground.
-- Gordon Robots for Less at Budget Robotics: http://www.budgetrobotics.com/ Author: Robot Builder's Sourcebook & Robot Builder's Bonanza
Paul Perrone wrote:

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