mc68hc708mp16 Freescale Semiconductor, Inc, mc68hc708mp16 Datasheet - Page 144

• Manufacturer Part Number: mc68hc708mp16
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Pulse Width Modulator for Motor Control (PWMMC)
9.6.2 Dead-Time Insertion
Technical Data
144
When complementary operation is used, two additional features are
provided:
If independent operation is chosen, each PWM has its own PWM value
register.
As shown in
be used to drive top-side/bottom-side transistors.
When controlling DC-to-AC inverters such as this, the top and bottom
PWMs in one pair should never be active at the same time. In
12, if PWM1 and PWM2 were on at the same time, large currents would
flow through the two transistors as they discharge the bus capacitor. The
IGBTs could be weakened or destroyed.
Simply forcing the two PWMs to be inversions of each other is not always
sufficient. Since a time delay is associated with turning off the transistors
in the motor drive, there must be a “dead-time” between the deactivation
of one PWM and the activation of the other.
A dead-time can be specified in the dead-time write-once register. This
8-bit value specifies the number of CPU clock cycles to use for the dead-
time. The dead-time is not affected by changes in the PWM period
caused by the prescaler.
Dead-time insertion is achieved by feeding the top PWM outputs of the
PWM generator into dead-time generators, as shown in
Current sensing determines which PWM value of a PWM generator pair
to use for the TOP PWM in the next PWM cycle. (See
Correction.) When output control is enabled, the odd OUT bits, rather
than the PWM generator outputs, are fed into the dead-time generators.
(See
Pulse Width Modulator for Motor Control (PWMMC)
•
•
9.6.5 Output Port
Dead-time insertion
Separate top/bottom pulse width correction to correct for
distortions caused by the motor drive characteristics.
Figure
9-12, in complementary mode, each PWM pair can
Control.)
MC68HC708MP16
Freescale Semiconductor
9.6.3 Top/Bottom
Figure
Figure 9-
—
9-13.
Rev. 3.1