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Chapter 14 Pulse Width Modulator with Fault Protection (PMF15B6CV3)
MC9S12ZVM Family Reference Manual Rev. 1.3
Freescale Semiconductor
535
Sampled results will be DT0 = 0 and DT1 = 1. Thus, the best time to change one PWM value register to
another is just before the current zero crossing.
Figure 14-57. Output Voltage Waveforms
14.4.6.2
Current-Sensing Correction
A current sense input, IS, for a PWM pair selects either the odd or the even PWM value registers to use in
the next PWM cycle. The selection is based on user-provided current sense circuitry driving the related IS
input high for negative current and low for positive current.
Previously shown, the current direction can be determined by the output voltage during deadtime. Thus, a
simple external voltage sensor can be used when current status is completed during deadtime, ISENS = 10.
Deadtime does not exist at the 100 percent and zero percent duty cycle boundaries. Therefore, the second
automatic mode must be used for correction, ISENS = 11, where current status is sampled at the half cycle
Table 14-42. Top/Bottom Current Sense Correction
Pin
Logic State
Output Control
IS0
0
PMFVAL0 controls PWM0/PWM1 pair
1
PMFVAL1 controls PWM0/PWM1 pair
IS1
0
PMFVAL2 controls PWM2/PWM3 pair
1
PMFVAL3 controls PWM2/PWM3 pair
IS2
0
PMFVAL4 controls PWM4/PWM5 pair
1
PMFVAL5 controls PWM4/PWM5 pair
DEADTIME
PWM TO TOP
POSITIVE
NEGATIVE
PWM TO BOTTOM
LOAD VOLTAGE WITH
LOAD VOLTAGE WITH
TRANSISTOR
TRANSISTOR
HIGH POSITIVE CURRENT
LOW POSITIVE CURRENT
CURRENT
CURRENT
LOAD VOLTAGE WITH
HIGH NEGATIVE CURRENT
LOAD VOLTAGE WITH
NEGATIVE CURRENT
T
B
T
B
T = DEADTIME INTERVAL BEFORE ASSERTION OF TOP PWM
B = DEADTIME INTERVAL BEFORE ASSERTION OF BOTTOM PWM
V+