PIC18F4321 Datasheet, PDF (158/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with 10-Bit A/D and nanoWatt Technology

PIC18F4321 FAMILY
16.4.6 PROGRAMMABLE DEAD-BAND
DELAY
Note:
Programmable dead-band delay is not
implemented in 28-pin devices with
standard CCP modules.
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 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 nonactive
state to the active state (see Figure 16-4 for illustration).
Bits PDC6:PDC0 of the ECCP1DEL register
(Register 16-2) set the delay period in terms of micro-
controller instruction cycles (TCY or 4 TOSC). These bits
are not available on 28-pin devices as the standard CCP
module does not support half-bridge operation.
16.4.7 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
comparator modules, a low level on the Fault input pin
(FLT0) 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 low digital signal on FLT0 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
ECCPAS2:ECCPAS0 bits (ECCP1AS<6:4>).
When a shutdown occurs, the output pins are asyn-
chronously placed in their shutdown states, specified
by the PSSAC1:PSSAC0 and PSSBD1:PSSBD0 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 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: Writing to the ECCPASE bit is disabled
while a shutdown condition is active.
REGISTER 16-2:
ECCP1DEL: PWM DEAD-BAND DELAY REGISTER
R/W-0
PRSEN
R/W-0
PDC6⁽¹⁾
R/W-0
PDC5⁽¹⁾
R/W-0
PDC4⁽¹⁾
R/W-0
PDC3⁽¹⁾
R/W-0
PDC2⁽¹⁾
bit 7
R/W-0
PDC1⁽¹⁾
R/W-0
PDC0⁽¹⁾
bit 0
bit 7
bit 6-0
PRSEN: PWM Restart Enable bit
1 = Upon auto-shutdown, the ECCPASE bit clears automatically once the shutdown event
goes away; the PWM restarts automatically
0 = Upon auto-shutdown, ECCPASE must be cleared in software to restart the PWM
PDC6:PDC0: PWM Delay Count bits⁽¹⁾
Delay time, in number of FOSC/4 (4 * TOSC) cycles, between the scheduled and actual time for
a PWM signal to transition to active.
Note 1: Unimplemented on 28-pin devices; bits read ‘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
DS39689E-page 156
Preliminary
© 2007 Microchip Technology Inc.