PIC18F258-ESLASHSOSQTP datasheet(140/402 Pages) MICROCHIP

140 / 402 page

PIC18FXX8

DS41159E-page 138

FIGURE 16-6:

EXAMPLE OF FULL-BRIDGE APPLICATION

16.5.3.1

Direction Change in Full-Bridge

Mode

In the Full-Bridge Output mode, the EPWM1M1 bit in

the ECCP1CON register allows the user to control the

forward/reverse direction. When the application firm-

ware changes this direction control bit, the ECCP1

module will assume the new direction on the next PWM

cycle. The current PWM cycle still continues, however,

the non-modulated outputs, P1A and P1C signals, will

transition to the new direction TOSC, 4 TOSC or 16 TOSC

earlier (for T2CKRS<1:0> = 00, 01 or 1x, respectively)

before the end of the period. During this transition

cycle, the modulated outputs, P1B and P1D, will go to

the inactive state (Figure 16-7).

Note that in the Full-Bridge Output mode, the ECCP

module does not provide any dead-band delay. In

general, since only one output is modulated at all times,

dead-band delay is not required. However, there is a

situation where a dead-band delay might be required.

This situation occurs when all of the following

conditions are true:

The direction of the PWM output changes when

the duty cycle of the output is at or near 100%.

The turn-off time of the power switch, including

the power device and driver circuit, is greater

than turn-on time.

Figure 16-8 shows an example where the PWM

direction changes from forward to reverse at a near

100% duty cycle. At time t1, the outputs P1A and P1D

become inactive, while output P1C becomes active. In

this example, since the turn-off time of the power

devices is longer than the turn-on time, a shoot-through

current flows through power devices QB and QD (see

Figure 16-6) for the duration of ‘t’. The same phenom-

enon will occur to power devices QA and QC for PWM

direction change from reverse to forward.

If changing PWM direction at high duty cycle is required

for an application, one of the following requirements

must be met:

Avoid changing PWM output direction at or near

100% duty cycle.

Use switch drivers that compensate the slow

turn off of the power devices. The total turn-off

time (toff) of the power device and the driver

must be less than the turn-on time (ton).

PIC18F448/458

P1D

P1B

FET

Driver

FET

Driver

V+

V-

Load

FET

Driver

FET

Driver

P1C

P1A

PIC18F258-E/SOSQTP 数据表(PDF) 140 Page - Microchip Technology

PIC18F258-E/SOSQTP 数据表(HTML) 140 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表下载

链接网址

PIC18F258-E/SOSQTP 数据表(PDF) 140 Page - Microchip Technology

PIC18F258-E/SOSQTP 数据表(HTML) 140 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

数据表 下载

链接网址

数据表下载