PIC16F1938 Datasheet, PDF (226/452 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers

PIC16(L)F1938/9
23.4.5
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 23-16 for
illustration. The lower seven bits of the associated
PWMxCON register (Register 23-5) sets the delay
period in terms of microcontroller instruction cycles
(TCY or 4 TOSC).
FIGURE 23-16:
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 23-17: EXAMPLE OF HALF-BRIDGE APPLICATIONS
V+
Standard Half-Bridge Circuit (“Push-Pull”)
FET
Driver
+
PxA
V
-
FET
Driver
PxB
Load
+
V
-
V-
DS41574A-page 226
Preliminary
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