PIC16F684T-I Datasheet, PDF (97/192 Pages) Microchip Technology – 14-Pin, Flash-Based 8-Bit CMOS Microcontrollers

PIC16F684
11.4.6
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 Section FIGURE 11-17:
“Example of Half-Bridge Applications” for
illustration. The lower seven bits of the associated
PWM1CON register (Register 11-3) sets the delay
period in terms of microcontroller instruction cycles
(TCY or 4 TOSC).
FIGURE 11-16:
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 11-17: EXAMPLE OF HALF-BRIDGE APPLICATIONS
V+
Standard Half-Bridge Circuit (“Push-Pull”)
FET
Driver
+
P1A
V
-
FET
Driver
P1B
Load
+
V
-
V-
© 2007 Microchip Technology Inc.
DS41202F-page 95