PIC16F1847_13 Datasheet, PDF (222/440 Pages) Microchip Technology – 18/20/28-Pin Flash Microcontrollers with XLP Technology

PIC16(L)F1847
24.4.5 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 24-16 for
illustration. The lower seven bits of the associated
PWMxCON register (Figure 24-4) sets the delay period
in terms of microcontroller instruction cycles (TCY or 4
TOSC).
FIGURE 24-16:
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 24-17: EXAMPLE OF HALF-BRIDGE APPLICATIONS
V+
Standard Half-Bridge Circuit (“Push-Pull”)
FET
Driver
+
PxA
V
-
FET
Driver
PxB
Load
+
V
-
V-
DS40001453D-page 222
Preliminary
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