PIC18F25K80 MICROCHIP [Microchip Technology], PIC18F25K80 Datasheet - Page 283

• Manufacturer Part Number: PIC18F25K80
• Manufacturer: MICROCHIP [Microchip Technology]

20.4.2.1
In the Full-Bridge mode, the P1M1 bit in the CCP1CON
register allows users to control the forward/reverse
direction. When the application firmware changes this
direction control bit, the module will change to the new
direction on the next PWM cycle.
A direction change is initiated in software by changing
the P1M1 bit of the CCP1CON register. The following
sequence occurs prior to the end of the current PWM
period:
• The modulated outputs (P1B and P1D) are placed
• The associated unmodulated outputs (P1A and
• PWM modulation resumes at the beginning of the
For an illustration of this sequence, see
The Full-Bridge mode does not provide a dead-band
delay. As one output is modulated at a time, a
dead-band delay is generally not required. There is a
situation where a dead-band delay is required. This
situation occurs when both of the following conditions
are true:
FIGURE 20-10:
 2011 Microchip Technology Inc.
in their inactive state.
P1C) are switched to drive in the opposite
direction.
next period.
Note 1: The direction bit, P1M1 of the CCP1CON register, is written any time during the PWM cycle.
P1A (Active-High)
P1B (Active-High)
P1C (Active-High)
P1D (Active-High)
2: When changing directions, the P1A and P1C signals switch before the end of the current PWM cycle. The
Signal
Direction Change in Full-Bridge
Mode
modulated P1B and P1D signals are inactive at this time. The length of this time is:
(1/F
OSC
) • TMR2 Prescale Value.
EXAMPLE OF PWM DIRECTION CHANGE
Pulse Width
Figure
Period
20-10.
Preliminary
(1)
PIC18F66K80 FAMILY
• The direction of the PWM output changes when
• The turn-off time of the power switch, including
Figure 20-11
changing from forward to reverse, at a near 100% duty
cycle. In this example, at time, t1, the P1A and P1D
outputs become inactive, while the P1C output
becomes active. Since the turn-off time of the power
devices is longer than the turn-on time, a shoot-through
current will flow through power devices, QC and QD
(see
phenomenon will occur to power devices, QA and QB,
for PWM direction change from reverse to forward.
If changing PWM direction at high duty cycle is required
for an application, two possible solutions for eliminating
the shoot-through current are:
• Reduce PWM duty cycle for one PWM period
• Use switch drivers that can drive the switches off
Other options to prevent shoot-through current may
exist.
the duty cycle of the output is at or near 100%.
the power device and driver circuit, is greater than
the turn-on time.
before changing directions.
faster than they can drive them on.
Figure
Pulse Width
20-8), for the duration of ‘t’. The same
(2)
shows an example of the PWM direction
Period
DS39977C-page 283