PIC18F2682 Datasheet, PDF (184/484 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with ECAN Technology, 10-Bit A/D and nanoWatt Technology

PIC18F2682/2685/4682/4685
16.4.6 PROGRAMMABLE DEAD-BAND
DELAY
Note:
Programmable dead-band delay is not
implemented in PIC18F2682/2685 devices
with standard CCP1 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 cur-
rent from destroying the bridge power switches. The delay
occurs at the signal transition from the non-active 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 microcontroller instruction
cycles (TCY or 4 TOSC). These bits are not available on
PIC18F2682/2685 devices, as the standard CCP1
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
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, a low level on 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 ECCPAS2:ECCPAS0 bits (bits<6:4> of the
ECCP1AS register).
When a shutdown occurs, the output pins are
asynchronously placed in their shutdown states, spec-
ified by the PSSAC1:PSSAC0 and PSSBD1:PSSBD0
bits (ECCP1AS3:ECCP1AS0). 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⁽¹⁾
R/W-0
PRSEN
bit 7
R/W-0
PDC6
R/W-0
PDC5
R/W-0
PDC4
R/W-0
PDC3
R/W-0
PDC2
R/W-0
PDC1
R/W-0
PDC0
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
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
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: This register is available on PIC18F4682/4685 devices only.
DS39761B-page 182
Preliminary
© 2007 Microchip Technology Inc.