BRUSHLESS DC MOTOR CONTROLLER

2007-3-16

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FSP33035

Three Phase Closed Loop Controller

The FSP33035, by itself, is only capable of open loop motor speed control. For closed loop motor speed control, the

FSP33035 requires an input voltage proportional to the motor speed. Traditionally, this has been accomplished by

means of a tachometer to generate the motor speed feedback voltage. Figure below shows an application whereby

an MC33039, powered from the 6.25 V reference (Pin 8) of the FSP33035, is used to generate the required

feedback voltage without the need of a costly tachometer. The same Hall sensor signals used by the FSP33035 for

rotor position decoding are utilized by the MC33039. Every positive or negative going transition of the Hall sensor

signals on any of the sensor lines causes the MC33039 to produce an output pulse of defined amplitude and time

duration, as determined by the external resistor R1 and capacitor C1. The output train of pulses at Pin 5 of the

MC33039 are integrated by the error amplifier of the FSP33035 configured as an integrator to produce a DC

voltage level which is proportional to the motor speed. This speed proportional voltage establishes the PWM

reference level at Pin 13 of the FSP33035 motor controller and closes the feedback loop. The FSP33035 outputs

drive a TMOS power MOSFET 3–phase bridge. High currents can be expected during conditions of start–up,

breaking, and change of direction of the motor. The system shown in the below Figure is designed for a motor

having 120/240 degrees Hall sensor electrical phasing. The system can easily be modified to accommodate 60/300

degree Hall sensor electrical phasing by removing the jumper (J2) at Pin 22 of the FSP33035.

Closed Loop Brushless DC Motor Control Using the FSP33035 and MC33039