PIC16F684 datasheet(97/192 Pages) MICROCHIP

97 / 192 page

DS41202F-page 95

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.

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.

Half-Bridge

mode,

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

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

FIGURE 11-17:

EXAMPLE OF HALF-BRIDGE APPLICATIONS

Period

Pulse Width

(1)

P1A(2)

P1B(2)

td = Dead-Band Delay

Period

(1)

Note 1:

At this time, the TMR2 register is equal to the

PR2 register.

Output signals are shown as active-high.

P1A

P1B

FET

Driver

FET

Driver

V+

V-

Load

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

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