BRUSHLESS DC MOTOR CONTROLLER
FSP33035
Brush Motor Control
Though the FSP33035 was designed to control brushless DC motors, it may also be used to control DC brush type
motors. Figure in page 22 shows an application of the FSP33035 driving a MOSFET H–bridge affording minimal
parts count to operate a brush–type motor. Key to the operation is the input sensor code [100] which produces a
top–left (Q1) and a bottom–right (Q3) drive when the controller’s forward/reverse pin is at logic [1]; top–right (Q4),
bottom–left (Q2) drive is realized when the Forward/Reverse pin is at logic [0]. This code supports the requirements
necessary for H–bridge drive accomplishing both direction and speed control.
The controller functions in a normal manner with a pulse width modulated frequency of approximately 25 kHz. Motor
speed is controlled by adjusting the voltage presented to the noninverting input of the error amplifier establishing the
PWM’s slice or reference level. Cycle–by–cycle current limiting of the motor current is accomplished by sensing the
voltage (100 mV) across the RS resistor to ground of the H–bridge motor current. The over current sense circuit
makes it possible to reverse the direction of the motor, using the normal forward/reverse switch, on the fly and not
have to completely stop before reversing.
LAYOUT CONSIDERSIONS
Do not attempt to construct any of the brushless motor control circuits on wire–wrap or plug–in prototype
boards. High frequency printed circuit layout techniques are imperative to prevent pulse jitter. This is usually caused
by excessive noise pick–up imposed on the current sense or error amp inputs. The printed circuit layout should
contain a ground plane with low current signal and high drive and output buffer grounds returning on separate paths
back to the power supply input filter capacitor VM. Ceramic bypass capacitors (0.1 µF) connected close to the
integrated circuit at VCC , VC , Vref and the error amp noninverting input may be required depending upon circuit
layout. This provides a low impedance path for filtering any high frequency noise. All high current loops should be
kept as short as possible using heavy copper runs to minimize radiated EMI.
TYPICAL PERFORMANCE CHARACTERISTICS
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2007-3-16
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