mc68hc908mr24 Freescale Semiconductor, Inc, mc68hc908mr24 Datasheet - Page 150

• Manufacturer Part Number: mc68hc908mr24
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Pulse-Width Modulator for Motor Control
9.6.2 Dead-Time Insertion
Advance Information
150
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
Figure
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 with Motor Phase Current Polarity
control is enabled, the odd OUT bits, rather than the PWM generator
outputs, are fed into the dead-time generators. See
Port
Pulse-Width Modulator for Motor Control (PWMMC)
•
•
Control.
Dead-time insertion
Separate top/bottom pulse width correction to correct for
distortions caused by the motor drive characteristics
9-12, if PWM1 and PWM2 were on at the same time, large
Figure
9-12, in complementary mode, each PWM pair can
MC68HC908MR24
Sensing. When output
Freescale Semiconductor
9.6.5 PWM Output
9.6.3 Top/Bottom
Figure
—
9-13.
Rev. 4.1