SMC6MXX-XX Datasheet, PDF (13/15 Pages) Sensitron – Brushless DC Motor Driver Module in a Power Flatpack 80-200V, 50 Amp

SENSITRON
SEMICONDUCTOR
TECHNICAL DATA
DATA SHEET 1023, REV. D
SMC6MXX-XX
SMC6MXX-XX-1
Control Modes
Typically, speed regulation is achieved by regulating the average input voltage to the motor,
while torque regulation is achieved by current control. Voltage and current control loops may
be combined to achieve a specific speed-torque curve.
Voltage-Mode Control
Fig. 9 shows the implementation of a typical speed control loop. A voltage command
proportional to the desired speed is applied at pin4 and can be set by a potentiometer, R3.
The speed feedback signal is obtained by low-pass filtering the Tach, pin15, output using R1
and C1. Small signal compensation of the speed control loop is provided by an internal error
amplifier. The integrating capacitor C2 places a pole at 0 HZ and a zero in conjunction with
R2. This zero can be used to cancel the low-frequency motor pole and to cross the loop with –
20dB gain response.
The output of the error amplifier is connected to the PWM comparator. Since the motor speed
is proportion to the average phase voltage, the speed is controlled via duty cycle control.
For open loop speed control, pin 2 shall be shorted to pin 8. The error amplifier acts as a
voltage follower and buffer to the command input.
Cycle-by-cycle current limiting is provided by connecting pins 25 and 26 to pins 12 and 13.
The over-current limit is set by the over-current reference IocRef at pin 9. This reference is set
internally to 1.15V, and can be altered using a resistor externally, see equations (1) to (4) for
details. The current signal is filtered internally, and amplified with a gain of 5.
Current Mode Control
Fig. 10 shows the implementation of a typical torque control loop. A voltage command
proportional to the desired current is applied at pin 4 and can be set by a potentiometer, R3.
The current feedback signal, Iso at pin11, is obtained by the internal current sensor and the
absolute value amplifier. Small signal compensation of the feedback control loop is provided
by an internal error amplifier. The error amplifier output is connected to the PWM comparator.
Since the torque is proportional to the average phase current, the torque is controlled via duty
cycle control.
It is recommended to set the over-current limit reference IocRef at pin 9 at a value slightly
higher than the maximum peak command current. This will maintain the cycle-by-cycle
current limiting even if the error amplifier saturates during large signal disturbance.
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