Datasheet

© 2007 Microchip Technology Inc. DS39599G-page 145
PIC18F2220/2320/4220/4320
16.4.2 HALF-BRIDGE MODE
In the Half-Bridge Output mode, two pins are used as
outputs to drive push-pull loads. The PWM output sig-
nal is output on the RC2/CCP1/P1A pin, while the com-
plementary PWM output signal is output on the RD5/
PSP5/P1B pin (Figure 16-4). This mode can be used
for half-bridge applications, as shown in Figure 16-5, or
for full-bridge applications where four power switches
are being modulated with two PWM signals.
In Half-Bridge Output mode, the programmable dead
band delay can be used to prevent shoot-through
current in half-bridge power devices. The value of bits
PDC6:PDC0 sets the number of instruction cycles
before the output is driven active. If the value is greater
than the duty cycle, the corresponding output remains
inactive during the entire cycle. See Section 16.4.4
“Programmable Dead-Band Delay” for more details
of the dead band delay operations.
Since the P1A and P1B outputs are multiplexed with
the PORTC<2> and PORTD<5> data latches, the
TRISC<2> and TRISD<5> bits must be cleared to
configure P1A and P1B as outputs.
FIGURE 16-4: HALF-BRIDGE PWM
OUTPUT
FIGURE 16-5: EXAMPLES OF HALF-BRIDGE OUTPUT MODE APPLICATIONS
Period
Duty Cycle
td
td
(1)
P1A
(2)
P1B
(2)
td = Dead Band Delay
Period
(1) (1)
Note 1: At this time, the TMR2 register is equal to the PR2
register.
2: Output signals are shown as active-high.
PIC18F4220/4320
P1A
P1B
FET
Driver
FET
Driver
V+
V-
Load
+
V
-
+
V
-
FET
Driver
FET
Driver
V+
V-
Load
FET
Driver
FET
Driver
PIC18F4220/4320
P1A
P1B
Standard Half-Bridge Circuit (“Push-Pull”)
Half-Bridge Output Driving a Full-Bridge Circuit