Microchip Technology AC244045 Data Sheet

DS41440C-page 232

 2010-2012 Microchip Technology Inc.

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 

 for illustration.

The lower seven bits of the associated PWMxCON
register (

) sets the delay period in terms

of microcontroller instruction cycles (T

CY

 or 4 T

OSC

).

Period

Pulse Width

td

td

PxA

PxB

td = Dead-Band Delay

Period

Note 1: At this time, the TMRx register is equal to the

PRx register.

2: Output signals are shown as active-high.

PxA

PxB

FET

Driver

FET

Driver

V+

V-

Load

+

V

-

+

V

-