Microchip Technology IC MCU 8BIT PIC18F65K22-I/PT TQFP-64 MCP PIC18F65K22-I/PT Data Sheet
Product codes
PIC18F65K22-I/PT
2009-2011 Microchip Technology Inc.
DS39960D-page 275
PIC18F87K22 FAMILY
20.4.6
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 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. For an illustration, see
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. For an illustration, see
. The lower seven bits of the associated
ECCPxDEL register (
) set the delay
period in terms of microcontroller instruction cycles
(T
(T
CY
or 4 T
OSC
).
FIGURE 20-14:
EXAMPLE OF
HALF-BRIDGE PWM
OUTPUT
HALF-BRIDGE PWM
OUTPUT
FIGURE 20-15:
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 TMR2 register is equal to the
PR2 register.
PR2 register.
2:
Output signals are shown as active-high.
PxA
PxB
FET
Driver
FET
Driver
V+
V-
Load
+
V
-
+
V
-
Standard Half-Bridge Circuit (“Push-Pull”)