PIC18LF2X_13 Datasheet, PDF (199/560 Pages) Microchip Technology – PIC18(L)F2X/45K50 USB Flash MCU Product Brief

PIC18(L)F2X/4XK22
14.4.5 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 14-16 for illustration.
The lower seven bits of the associated PWMxCON
register (Register 14-6) sets the delay period in terms
of microcontroller instruction cycles (TCY or 4 TOSC).
FIGURE 14-16:
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: At this time, the TMRx register is equal to the
PRx register.
2: Output signals are shown as active-high.
FIGURE 14-17: EXAMPLE OF HALF-BRIDGE APPLICATIONS
V+
Standard Half-Bridge Circuit (“Push-Pull”)
FET
Driver
+
PxA
V
-
FET
Driver
PxB
Load
+
V
-
V-
 2010-2012 Microchip Technology Inc.
DS41412F-page 199