PIC12F1822 MICROCHIP [Microchip Technology], PIC12F1822 Datasheet - Page 214

• Manufacturer Part Number: PIC12F1822
• Description: 8/14-Pin Flash Microcontrollers with nanoWatt XLP Technology
• Manufacturer: MICROCHIP [Microchip Technology]

PIC12F/LF1822/16F/LF1823
23.4.2.1
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 four Timer cycles 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
See Figure 23-12 for an illustration of this sequence.
FIGURE 23-12:
DS41413A-page 214
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)
Signal
2: When changing directions, the P1A and P1C signals switch before the end of the current PWM cycle. The
Direction Change in Full-Bridge
Mode
modulated P1B and P1D signals are inactive at this time. The length of this time is four Timer counts.
EXAMPLE OF PWM DIRECTION CHANGE
Pulse Width
Period
(1)
Preliminary
The Full-Bridge mode does not provide dead-band
delay. As one output is modulated at a time, dead-band
delay is generally not required. There is a situation
where dead-band delay is required. This situation
occurs when both of the following conditions are true:
1.
2.
Figure 23-13 shows an example of the PWM direction
changing from forward to reverse, at a near 100% duty
cycle. In this example, at time t1, the output P1A and
P1D become inactive, while output P1C 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
Figure 23-10) for the duration of ‘t’. The same
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:
1.
2.
Other options to prevent shoot-through current may
exist.
The direction of the PWM output changes when
the duty cycle of the output is at or near 100%.
The turn-off time of the power switch, including
the power device and driver circuit, is greater
than the turn-on time.
Reduce PWM duty cycle for one PWM period
before changing directions.
Use switch drivers that can drive the switches off
faster than they can drive them on.
Pulse Width
(2)
Period
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