PIC18F97J60_11 Datasheet, PDF (211/492 Pages) Microchip Technology – 64/80/100-Pin, High-Performance, 1-Mbit Flash Microcontrollers with Ethernet

PIC18F97J60 FAMILY
18.4.6
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 flow-
ing 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
transition from the non-active state to the active state.
See Figure 18-4 for the illustration. The lower seven
bits of the ECCP1DEL register (Register 18-2) set the
delay period in terms of microcontroller instruction
cycles (TCY or 4 TOSC).
18.4.7
ENHANCED PWM
AUTO-SHUTDOWN
When the ECCP1 is programmed for any of the
Enhanced PWM modes, the active output pins may be
configured for auto-shutdown. Auto-shutdown immedi-
ately 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 two
comparator modules or the FLT0 pin (or any combina-
tion 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 low-level digital
signal on the FLT0 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 ECCP1AS<2:0> bits
(ECCP1AS<6:4>).
When a shutdown occurs, the output pins are
asynchronously placed in their shutdown states,
specified by the PSS1AC<1:0> and PSS1BD<1:0> bits
(ECCP1AS<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 ECCP1ASE bit
(ECCP1AS<7>) is also set to hold the Enhanced PWM
outputs in their shutdown states.
The ECCP1ASE bit is set by hardware when a shutdown
event occurs. If automatic restarts are not enabled, the
ECCP1ASE bit is cleared by firmware when the cause of
the shutdown clears. If automatic restarts are enabled,
the ECC1PASE bit is automatically cleared when the
cause of the auto-shutdown has cleared.
If the ECCP1ASE bit is set when a PWM period begins,
the PWM outputs remain in their shutdown state for that
entire PWM period. When the ECCP1ASE bit is cleared,
the PWM outputs will return to normal operation at the
beginning of the next PWM period.
Note: Writing to the ECCP1ASE bit is disabled
while a shutdown condition is active.
REGISTER 18-2: ECCP1DEL: ECCP1 DEAD-BAND DELAY REGISTER
R/W-0
P1RSEN
bit 7
R/W-0
P1DC6
R/W-0
P1DC5
R/W-0
P1DC4
R/W-0
P1DC3
R/W-0
P1DC2
R/W-0
P1DC1
R/W-0
P1DC0
bit 0
Legend:
R = Readable bit
-n = Value at POR
W = Writable bit
‘1’ = Bit is set
U = Unimplemented bit, read as ‘0’
‘0’ = Bit is cleared
x = Bit is unknown
bit 7
bit 6-0
P1RSEN: PWM Restart Enable bit
1 = Upon auto-shutdown, the ECCP1ASE bit clears automatically once the shutdown event goes
away; the PWM restarts automatically
0 = Upon auto-shutdown, ECCP1ASE must be cleared in software to restart the PWM
P1DC<6:0>: PWM Delay Count bits
Delay time, in number of FOSC/4 (4 * TOSC) cycles, between the scheduled time and actual time for a
PWM signal to transition to active.
 2011 Microchip Technology Inc.
DS39762F-page 211