PIC18F44J50-I Datasheet, PDF (263/562 Pages) Microchip Technology – 28/44-Pin, Low-Power, High-Performance USB Microcontrollers

PIC18F46J50 FAMILY
18.5.6
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 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 18-16 for
illustration. The lower seven bits of the associated
ECCPxDEL register (Register 18-3) set the delay
period in terms of microcontroller instruction cycles
(TCY or 4 TOSC).
FIGURE 18-16:
EXAMPLE OF
HALF-BRIDGE PWM
OUTPUT
Period
Period
PxA⁽²⁾
Pulse Width
td
td
PxB⁽²⁾
(1)
(1)
(1)
td = Dead-Band Delay
Note 1:
2:
At this time, the TMR2 register is equal to the
PR2 register.
Output signals are shown as active-high.
FIGURE 18-17: EXAMPLE OF HALF-BRIDGE APPLICATIONS
V+
Standard Half-Bridge Circuit (“Push-Pull”)
FET
Driver
+
PxA
V
-
FET
Driver
PxB
Load
+
V
-
V-
 2011 Microchip Technology Inc.
DS39931D-page 263