PIC16F716 Microchip Technology, PIC16F716 Datasheet - Page 46

• Manufacturer Part Number: PIC16F716
• Description: 8-bit Flash-based Microcontroller with A/D Converter and Enhanced Capture/Compare/PWM
• Manufacturer: Microchip Technology

PIC16F716
Figure 7-14 shows an example where the PWM
direction changes from forward to reverse, at a near
100% duty cycle. At time t1, the output P1A and P1D
become inactive, while output P1C becomes active. In
this example, since the turn-off time of the power
devices is longer than the turn-on time, a shoot-through
current may flow through power devices QC and QD
(see Figure 7-12) for the duration of ‘t’. The same
phenomenon will occur to power devices QA and QB
for PWM direction change from reverse to forward.
FIGURE 7-13:
FIGURE 7-14:
DS41206A-page 44
Note 1:
Note 1:
P1A (Active-High)
P1B (Active-High)
P1C (Active-High)
P1D (Active-High)
External Switch C
External Switch D
2:
Potential
Shoot-Through
Current
SIGNAL
2:
3:
The direction bit in the CCP1 Control Register (CCP1CON<7>) is written any time during the PWM cycle.
When changing directions, the P1A and P1C signals switch before the end of the current PWM cycle at intervals of
4 T
inactive at this time.
OSC
All signals are shown as active-high.
t
t
on
off
is the turn-on delay of power switch QC and its driver.
is the turn-off delay of power switch QD and its driver.
, 16 T
P1A
P1B
P1C
P1D
PWM DIRECTION CHANGE
PWM DIRECTION CHANGE AT NEAR 100% DUTY CYCLE
OSC
or 64 T
DC
OSC
, depending on the Timer2 prescaler value. The modulated P1B and P1D signals are
Forward Period
Period
DC
(1)
Preliminary
If changing PWM direction at high duty cycle is required
for an application, one of the following requirements
must be met:
1.
2.
Other options to prevent shoot-through current may
exist.
t1
Reduce PWM for a PWM period before changing
directions.
Use switch drivers that can drive the switches off
faster than they can drive them on.
DC
(Note 2)
t
on
Reverse Period
t
t = t
off
Period
off
DC
- t
 2003 Microchip Technology Inc.
on