PIC18LF4331-ESLASHML datasheet(193/392 Pages) MICROCHIP

193 / 392 page

 2010 Microchip Technology Inc.

DS39616D-page 193

PIC18F2331/2431/4331/4431

The actual dead time is calculated from the DTCON

Dead Time = Dead-Time Value/(FOSC/Prescaler)

Table 18-3 shows example dead-time ranges as a

function of the input clock prescaler selected and the

device operating frequency.

TABLE 18-3:

EXAMPLE DEAD-TIME

RANGES

18.7.4

DEAD-TIME DISTORTION

18.8

Independent PWM Output

Independent PWM mode is used for driving the loads

(as shown in Figure 18-19) 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

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.

18.8.1

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 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 18-3 and Register 18-4).

FOSC

(MHz)

MIPS

Prescaler

Selection

Dead-Time

Min

Dead-Time

Max

FOSC/2

50 ns

3.2

s

FOSC/4

100 ns

6.4

s

FOSC/8

200 ns

12.8

s

FOSC/16

400 ns

25.6

s

FOSC/2

62.5 ns

s

FOSC/4

125 ns

s

FOSC/8

250 ns

s

FOSC/16

500 ns

s

6.25

FOSC/2

80 ns

5.12

s

6.25

FOSC/4

160 ns

10.2

s

6.25

FOSC/8

320 ns

20.5

s

6.25

FOSC/16

640 ns

s

FOSC/2

100 ns

6.4

s

FOSC/4

200 ns

12.8

s

FOSC/8

400 ns

25.6

s

FOSC/16

800 ns

51.2

s

2.5

FOSC/2

200 ns

12.8

s

2.5

FOSC/4

400 ns

25.6

s

2.5

FOSC/8

800 ns

51.2

s

2.5

FOSC/16

1.6

s

102.4

s

51.25

FOSC/2

400 ns

25.6

s

51.25

FOSC/4

800 ns

51.2

s

51.25

FOSC/8

1.6

s

102.4

s

51.25

FOSC/16

3.2

s

204.8

s

FOSC/2

0.5

s32 s

FOSC/4

s64 s

FOSC/8

s

128

s

FOSC/16

s

256

s

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

module. 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.

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

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