PIC18F23K20_10 Datasheet, PDF (185/456 Pages) Microchip Technology – 28/40/44-Pin Flash Microcontrollers with nanoWatt XLP Technology

PIC18F2XK20/4XK20
16.4.6 PROGRAMMABLE DEAD-BAND
DELAY MODE
In Half-Bridge applications where all power switches
are modulated at the PWM frequency, the power
switches normally require more time to turn off than to
turn on. If both the upper and lower power switches are
switched at the same time (one turned on, and the
other turned off), both switches may be on for a short
period of time until one switch completely turns off.
During this brief interval, a very high current
(shoot-through current) will flow through both power
switches, shorting the bridge supply. To avoid this
potentially destructive shoot-through current from
flowing during switching, turning on either of the power
switches is normally delayed to allow the other switch
to completely turn off.
In Half-Bridge mode, a digitally programmable
dead-band delay is available to avoid shoot-through
current from destroying the bridge power switches. The
delay occurs at the signal transition from the non-active
state to the active state. See Figure 16-12 for
illustration. The lower seven bits of the associated
PWM1CON register (Register 16-3) sets the delay
period in terms of microcontroller instruction cycles
(TCY or 4 TOSC).
FIGURE 16-12:
EXAMPLE OF
HALF-BRIDGE PWM
OUTPUT
Period
Period
P1A⁽²⁾
Pulse Width
td
td
P1B⁽²⁾
(1)
(1)
(1)
td = Dead-Band Delay
Note 1: At this time, the TMR2 register is equal to the
PR2 register.
2: Output signals are shown as active-high.
FIGURE 16-13: EXAMPLE OF HALF-BRIDGE APPLICATIONS
V+
Standard Half-Bridge Circuit (“Push-Pull”)
FET
Driver
+
P1A
V
-
FET
Driver
P1B
Load
+
V
-
V-
 2010 Microchip Technology Inc.
DS41303G-page 185