AN1794 datasheet(11/34 Pages) STMICROELECTRONICS

11 / 34 page

AN1794

BLDC motor drive

11/34

BLDC 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 BLDC motor drive, the system operates in an open loop duty cycle

control mode with cycle-by-cycle current limit.

5.1

BLDC 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.

Braking: toggle the "Brake when Stop" switch to the OFF position. 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 three 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 BLDC motors with several ohms of resistance do not pose a risk.

Current: set the current to approximately 25%. This is an initial guess as to the required

setting and may need further adjustment.

Voltage: set the voltage to approximately 50%.

Run: make sure that the motor is free to turn in either direction and click the run button.

The motor 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 motor does not run click the stop button, increase the current settings to 50%, and

click run button. If the motor still does 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.

AN1794 Datasheet(PDF) 11 Page - STMicroelectronics