12F615 datasheet(92/168 Pages) MICROCHIP

92 / 168 page

PIC12F609/615/12HV609/615

DS41302A-page 90

Preliminary

10.4.5

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 10-13 for illustration.

The lower seven bits of the associated PWMxCON

of microcontroller instruction cycles (TCY or 4 TOSC).

FIGURE 10-13:

EXAMPLE OF HALF-

BRIDGE PWM OUTPUT

FIGURE 10-14:

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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