SMC6MXX-XX Datasheet, PDF (12/15 Pages) Sensitron – Brushless DC Motor Driver Module in a Power Flatpack 80-200V, 50 Amp

SENSITRON
SEMICONDUCTOR
SMC6MXX-XX
SMC6MXX-XX-1
TECHNICAL DATA
DATA SHEET 1023, REV. D
When configured in two-quadrant mode, Quad=0, SMC6MXX-XX modulates only the high-
side devices of the output power stage. The current paths within the output stage during the
PWM on and off times are illustrated in Fig. 6. During the on time, both switches S1 and S4
are on, the current flows through both switches and the motor winding. During the off time, the
upper switch S1 is shut off, and the motor current circulates through the lower switch S4 and
D2. The motor is assumed to be operated in quadrants I or III.
If operation is attempted in quadrants II or IV by changing the Dir input, S1 and S4 are turned
off and S2 and S3 are turned on. Under this condition motor current very quickly decays,
reverses direction and increases until the over-current limit is reached. At this point, S3 turns
off the current circulates in S2 and D4, and continue to rise due to the fact that the back emf
is in-phase with the current because the motor direction has not changed yet. Fig. 7 illustrates
the current path in this case. Under these conditions there is nothing to limit the current other
than the controller and the motor impedance. These circulating currents can result in damage
to the power stage if the load inertia is high.
In four-quadrant mode, Quad=1, both upper and lower switches are modulated. Motor current
always decays during off time, eliminating any uncontrolled circulating current. In addition, the
current always flows through the current sense resistor. Fig. 8 illustrates the current paths
during torque reversal.
It is recommended in two-quadrant operation to utilize the speed input, pin 23, for safe
direction reversal. The direction input can be latched by speed input. As long as Speed-in is
less than 0.250V, the direction latch is transparent. When Speed-in is higher than 0.250V
changing direction of rotation will enable coast until the Speed-in drops below 0.250V. The
Speed-in signal is obtained by low-pass filtering the Tach output, pin 15, using RC filter.
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