PIC18F4580-ESLASHML datasheet(186/490 Pages) MICROCHIP

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PIC18F2480/2580/4480/4580

DS39637D-page 186

17.4.6

PROGRAMMABLE DEAD-BAND

DELAY

In half-bridge applications where all power switches are

modulated at the PWM frequency at all times, 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)

may 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 the Half-Bridge Output mode, a digitally program-

mable, dead-band delay is available to avoid

shoot-through current from destroying the bridge

power switches. The delay occurs at the signal transi-

tion from the non-active state to the active state (see

Figure 17-4 for illustration). Bits, PDC<6:0< of the

ECCP1DEL register (Register 17-2), set the delay

period in terms of microcontroller instruction cycles

(TCY or 4 TOSC). These bits are not available on

PIC18F2X80 devices, as the standard CCP module

does not support half-bridge operation.

17.4.7

ENHANCED PWM AUTO-SHUTDOWN

When the CCP1 is programmed for any of the Enhanced

PWM modes, the active output pins may be configured

for auto-shutdown. Auto-shutdown immediately places

the Enhanced PWM output pins into a defined shutdown

state when a shutdown event occurs.

A shutdown event can be caused by either of the

comparator

modules,

low

level

the

RB0/INT0/FLT0/AN10 pin, or any combination of these

three sources. The comparators may be used to monitor

a voltage input proportional to a current being monitored

in the bridge circuit. If the voltage exceeds a threshold,

the comparator switches state and triggers a shutdown.

Alternatively, a digital signal on the INT0 pin can also

trigger a shutdown. The auto-shutdown feature can be

disabled by not selecting any auto-shutdown sources.

The auto-shutdown sources to be used are selected

using the ECCPAS<2:0> bits (ECCP1AS<6:4>).

When a shutdown occurs, the output pins are

asynchronously placed in their shutdown states,

specified by the PSSAC<1:0> and PSS1BD<1:0> bits

(ECCPAS<3:0>). Each pin pair (P1A/P1C and P1B/P1D)

may be set to drive high, drive low or be tri-stated (not

driving). The ECCPASE bit (ECCP1AS<7>) is also set to

hold the Enhanced PWM outputs in their shutdown

states.

The ECCPASE bit is set by hardware when a shutdown

event occurs. If automatic restarts are not enabled, the

ECCPASE bit is cleared by firmware when the cause of

the shutdown clears. If automatic restarts are enabled,

the ECCPASE bit is automatically cleared when the

cause of the auto-shutdown has cleared.

If the ECCPASE bit is set when a PWM period begins,

the PWM outputs remain in their shutdown state for that

entire PWM period. When the ECCPASE bit is cleared,

the PWM outputs will return to normal operation at the

beginning of the next PWM period.

Note:

Programmable dead-band delay is not

implemented in PIC18F2X80 devices with

standard CCP modules.

Note:

Writing to the ECCPASE bit is disabled

while a shutdown condition is active.

Note:

If the dead-band delay value is increased

after the dead-band time has elapsed, that

new value takes effect immediately. This

happens even if the PWM pulse is high

and can appear to be a glitch. Dead-band

values must be changed during the

dead-band time or before ECCP is active

PIC18F4580-E/ML Datasheet(PDF) 186 Page - Microchip Technology

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