PXS20RM Datasheet, PDF (672/1368 Pages) Freescale Semiconductor, Inc – PXS20 Microcontroller

Flexible Motor Control Pulse Width Modulator Module (FlexPWM)
T
B
T
B
DEADTIME
PWM TO TOP
TRANSISTOR
V+
POSITIVE
CURRENT
PWM TO BOTTOM
TRANSISTOR
LOAD VOLTAGE WITH
HIGH POSITIVE CURRENT
LOAD VOLTAGE WITH
LOW POSITIVE CURRENT
LOAD VOLTAGE WITH
HIGH NEGATIVE CURRENT
LOAD VOLTAGE WITH
LOW NEGATIVE CURRENT
NEGATIVE
CURRENT
T = DEADTIME INTERVAL BEFORE ASSERTION OF TOP PWM
B = DEADTIME INTERVAL BEFORE ASSERTION OF BOTTOM PWM
Figure 25-24. Output Voltage Waveforms
25.3.3.9 Output logic
Figure 25-25 shows the output logic of each submodule including how each PWM output has individual
fault disabling, polarity control, and output enable. This allows for maximum flexibility when interfacing
to the external circuitry.
The PWM23 and PWM45 signals which are output from the deadtime logic in Figure 25-25 are positive
true signals. In other words, a high level on these signals should result in the corresponding transistor in
the PWM inverter being turned ON. The voltage level required at the PWM output pin to turn the
transistor ON or OFF is a function of the logic between the pin and the transistor. Therefore, it is
imperative that the user program the POLA and POLB bits before enabling the output pins. A fault
condition can result in the PWM output being tristated, forced to a logic 1, or forced to a logic 0 depending
on the values programmed into the PWMxFS fields.
25-26
PXS20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor