PIC16LC717T-I/SO View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
PIC16LC717T-I/SO Datasheet PDF : 200 Pages
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PIC16C717/770/771
Note that in the Full-Bridge output mode, the ECCP
module does not provide any deadband delay. In gen-
eral, since only one output is modulated at all time,
deadband delay is not required. However, there is a sit-
uation where a deadband delay might be required. This
situation occurs when all of the following conditions are
true:
1. The direction of the PWM output changes when
the duty cycle of the output is at or near 100%.
2. The turn off time of the power switch, including
the power device and driver circuit, is greater
than turn on time.
Figure 8-11 shows an example, where the PWM direc-
tion 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
flows through the power devices, QB and QD, for the
duration of t= toff-ton. The same phenomenon will occur
to power devices, QC and QB, for PWM direction
change from reverse to forward.
If changing PWM direction at high duty cycle is required
for the user’s application, one of the following require-
ments must be met:
1. Avoid changing PWM output direction at or near
100% duty cycle.
2. Use switch drivers that compensate the slow
turn off of the power devices. The total turn off
time (toff) of the power device and the driver
must be less than the turn on time (ton).
FIGURE 8-11: PWM DIRECTION CHANGE AT NEAR 100% DUTY CYCLE
FORWARD PERIOD
REVERSE PERIOD
P1A
1
0
1
P1B 0
(PWM)
P1C
1
0
P1D
1
0
External Switch C
1
0
(PWM)
External Switch D
1
0
Potential
1
Shoot Through 0
Current
t1
Note 1: All signals are shown as active high.
2: ton is the turn on delay of power switch and driver.
3: toff is the turn off delay of power switch and driver.
ton
toff
t = toff - ton
© 1999 Microchip Technology Inc.
Advanced Information
DS41120A-page 65
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