Microchip Technology MA160014 Data Sheet
2010-2012 Microchip Technology Inc.
DS41412F-page 199
PIC18(L)F2X/4XK22
14.4.5
PROGRAMMABLE DEAD-BAND
DELAY MODE
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.
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
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
for illustration.
The lower seven bits of the associated PWMxCON
register (
register (
) sets the delay period in terms
of microcontroller instruction cycles (T
CY
or 4 T
OSC
).
FIGURE 14-16:
EXAMPLE OF HALF-
BRIDGE PWM OUTPUT
BRIDGE PWM OUTPUT
FIGURE 14-17:
EXAMPLE OF HALF-BRIDGE APPLICATIONS
Period
Pulse Width
td
td
(1)
PxA
(2)
PxB
(2)
td = Dead-Band Delay
Period
(1)
(1)
Note 1:
At this time, the TMRx register is equal to the
PRx register.
PRx register.
2:
Output signals are shown as active-high.
PxA
PxB
FET
Driver
Driver
FET
Driver
Driver
V+
V-
Load
+
V
V
-
+
V
V
-
Standard Half-Bridge Circuit (“Push-Pull”)