PIC16LF1824 datasheet(222/440 Pages) MICROCHIP

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PIC16(L)F1847

DS40001453D-page 222

Preliminary

 2011-2013 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 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

FIGURE 24-17:

EXAMPLE OF HALF-BRIDGE APPLICATIONS

Period

Pulse Width

(1)

PxA(2)

PxB(2)

td = Dead-Band Delay

Period

(1)

Note 1:

At this time, the TMRx register is equal to the

PRx register.

Output signals are shown as active-high.

PxA

PxB

FET

Driver

FET

Driver

V+

V-

Load

Standard Half-Bridge Circuit (“Push-Pull”)

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