AN1794 datasheet(10/34 Pages) STMICROELECTRONICS

10 / 34 page

DC motor drive

AN1794

10/34

DC motor drive

After the system has established the connection to the interface board, it will initialize the

settings to the last stored settings and open the appropriate practiSPIN software for the

selected motor type. For DC motor drive, the system operates in an open loop duty cycle

control mode with cycle-by-cycle current limit.

4.1

Dual DC motor control mode

Direction: in the direction box for each motor, click the toggle switch to pick forward or

reverse. This is somewhat arbitrary since we probably don't know what the direction

sense of the motor will be. Once the motor is running, toggle this switch to reverse the

motor direction if desired. To reverse the meaning of the forward and reverse

designations, disable the motor (orange disable button at bottom of screen) and then

swap the motor wires at either CN3 or CN4.

Braking: toggle the "Brake when Stop" switch to the OFF position for both motors. This

will cause the motor to coast to rest when stopped, with the bridge placed in a high

impedance state. If desired this function can later be toggled on but some care should

be exercised. Braking will effectively short out the motor armature through two

transistors in the bridge, which could cause excessive current and power dissipation if

the motor and load have a large moment of inertia (thus a large amount or stored

mechanical to be dissipated) or the motor has a very low resistance (resulting in a large

current flow). Most smaller DC motors with several ohms of resistance do not pose a

risk.

Current: set the current for both motors to approximately 25%. This is an initial guess

as to the required setting and may need further adjustment.

Voltage: set the voltage for both motors to approximately 50%.

Run: make sure that the motors are free to turn in either direction and click the run

button. the motors should come up to approximately half of the speed that would be

expected at this supply voltage. To change the motor direction, click the direction toggle

switch. If the motors do not run click the STOP button, increase both current settings to

50%, and click RUN button. If the motors still do not run an oscilloscope and current

probe should be used to observe the motor current

Stop: click stop to stop the motor.

After the basic operation of the system has been verified, adjust voltage, current, direction

and other parameters to evaluate the system.

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