Broken H-Bridge? (SN7544)

Hey All,

I just started a new project were I need to power up some motors which draw 7.4v using an arduino. I chose the SN7544 motor driver which I haven't been having a hard time using in the past, however I a coming across some problems. When I first hooked it up, the motors just "buzzed" and refused to move, while the IC itself got incredibly hot. I checked my wiring, it was good according to this tutorial (http://itp.nyu.edu/physcomp/Labs/DCMotorControl). Upon further inspection with my multimeter I believe to have found the problem. One of the motor terminal pins gives out a solid 7.4v when pulled high, but the other, supposed to be ground, is hovering at around .5-.53 volts. Is this a broken chip? Or do I need to add a resistor somewhere? I'm still kinda new with electronics so I'm not sure what my next step is.

This is a darlington driver, each output should fail to reach its rail by around 0.8 to 2.0V under load.

Excessive heat indicates over-driving, what is the motor, what supply, did you think to measure the actual current?

Darlington drivers always get warm at the least because they are so inefficient. Too hot to touch isn't necessarily a problem...

I am using a Dagu Thumper chassis that draws 7.2v and draws about 2.2 amps. My battery fits within the specs, I don't think its the problem. Following the tutorial I posted above exactly, I get no response and the motors just buzz. Looking at the pins I notice the HIGH pin is giving out 7.4v (good), yet the LOW pin hovering around .5v, which I believe to be the problem. Am I missing something else here?

So that means the motor is getting 7.4 - 0.5 = 6.9V then? Have you measure voltage at the motor terminals, at the supply, actual supply current? Double checked all the connections/wiring?

Have you tried the motor directly across the battery?

The motor should run with 1/2V loss across the Darlington driver, but you'll get slightly less speed & torque. There is always some drop across the driver, but a MOSFET will generally have less of a drop.

With a bridge driver, you get a drop across both sides of the bridge. The only way you're going to get 7.2V across the motor is to use a slightly higher supply voltage. Of course if you are driving it from an unregulated battery supply, the voltage will also drop as the battery discharges.