PIC18F2331_07 Datasheet, PDF (203/400 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
The actual dead time is calculated from the DTCON
register as follows:
Dead Time = Dead Time Value/(FOSC/Prescaler)
Table 17-3 shows example dead-time ranges as a
function of the input clock prescaler selected and the
device operating frequency.
TABLE 17-3: EXAMPLE DEAD-TIME
RANGES
FOSC
(MHz)
MIPS
Prescaler
Selection
Dead-Time Dead-Time
Min
Max
40
10
FOSC/2
40
10
FOSC/4
40
10
FOSC/8
40 10 FOSC/16
32
8
FOSC/2
32
8
FOSC/4
32
8
FOSC/8
32
8 FOSC/16
25 6.25 FOSC/2
25 6.25 FOSC/4
25 6.25 FOSC/8
25 6.25 FOSC/16
20
5
FOSC/2
20
5
FOSC/4
20
5
FOSC/8
20
5 FOSC/16
10 2.5 FOSC/2
10 2.5 FOSC/4
10 2.5 FOSC/8
10 2.5 FOSC/16
5 1.25 FOSC/2
5 1.25 FOSC/4
5 1.25 FOSC/8
5 1.25 FOSC/16
4
1
FOSC/2
4
1
FOSC/4
4
1
FOSC/8
4
1 FOSC/16
50 ns
100 ns
200 ns
400 ns
62.5 ns
125 ns
250 ns
500 ns
80 ns
160 ns
320 ns
640 ns
100 ns
200 ns
400 ns
800 ns
200 ns
400 ns
800 ns
1.6 μs
400 ns
800 ns
1.6 μs
3.2 μs
0.5 μs
1 μs
2 μs
4 μs
3.2 μs
6.4 μs
12.8 μs
25.6 μs
4 μs
8 μs
16 μs
32 μs
5.12 μs
10.2 μs
20.5 μs
41 μs
6.4 μs
12.8 μs
25.6 μs
51.2 μs
12.8 μs
25.6 μs
51.2 μs
102.4 μs
25.6 μs
51.2 μs
102.4 μs
204.8 μs
32 μs
64 μs
128 μs
256 μs
17.7.4 DEAD-TIME DISTORTION
Note 1: For small PWM duty cycles, the ratio of
dead time to the active PWM time may
become large. In this case, the inserted
dead time will introduce distortion into
waveforms produced by the PWM mod-
ule. The user can ensure that dead-time
distortion is minimized by keeping the
PWM duty cycle at least three times
larger than the dead time. A similar effect
occurs for duty cycles at or near 100%.
The maximum duty cycle used in the
application should be chosen such that
the minimum inactive time of the signal is
at least three times larger than the dead
time. If the dead time is greater or equal
to the duty cycle of one of the PWM
output pairs, then that PWM pair will be
inactive for the whole period.
2: Changing the dead-time values in
DTCON when the PWM is enabled may
result in an undesired situation. Disable
the PWM (PTEN = 0) before changing the
dead-time value
17.8 Independent PWM Output
Independent PWM mode is used for driving the loads
(as shown in Figure 17-19) for driving one winding of a
switched reluctance motor. A particular PWM output
pair is configured in the Independent Output mode
when the corresponding PMOD bit in the PWMCON0
register is set. No dead-time control is implemented
between the PWM I/O pins when the module is operat-
ing in the Independent PWM mode and both I/O pins
are allowed to be active simultaneously. This mode can
also be used to drive stepper motors.
17.8.1 DUTY CYCLE ASSIGNMENT IN THE
INDEPENDENT PWM MODE
In the Independent PWM mode, each duty cycle gener-
ator is connected to both PWM output pins in a given
PWM output pair. The odd and the even PWM output
pins are driven with a single PWM duty cycle generator.
PWM1 and PWM0 are driven by the PWM channel
which uses the PDC0 register to set the duty cycle,
PWM3 and PWM2 with PDC1, PWM5 and PWM4 with
PDC2 and PWM7 and PWM6 with PDC3 (see
Figure 17-3 and Register 17-4).
© 2007 Microchip Technology Inc.
Preliminary
DS39616C-page 201