PIC12F752 datasheet(85/204 Pages) MICROCHIP

85 / 204 page

 2011 Microchip Technology Inc.

Preliminary

DS41576A-page 85

PIC12F752/HV752

11.1

Fundamental Operation

The COG generates a two output complementary

PWM waveform from rising and falling event sources.

In the simplest configuration, the rising and falling

event sources are the same signal, which is a PWM

signal with the desired period and duty cycle. The COG

converts this single PWM input into a dual complemen-

tary PWM output. The frequency and duty cycle of the

dual PWM output match those of the single input PWM

signal. The off-to-on transition of each output can be

delayed from the on-to-off transition of the other output,

thereby, creating a time immediately after the PWM

transition where neither output is driven. This is

referred to as dead time and is covered in Section 11.5

“Dead-Band Control”.

A typical operating waveform, with dead band, generated

from a single CCP1 input is signal is shown in Figure 11-2.

The COG can also generate a PWM waveform from a

periodic rising event and a separate falling event. In

this case, the falling event is usually derived from

analog feedback within the external PWM driver circuit.

In this configuration, high power switching transients

may trigger a false falling event that needs to be

blanked out. The COG can be configured to blank

falling (and rising) event inputs for a period of time

immediately following the rising (and falling) event drive

output. This is referred to as input blanking and is

covered in Section 11.6 “Blanking Control”.

It may be necessary to guard against the possibility of

circuit faults or a feedback event arriving too late or not

at all. In this case, the active drive must be terminated

before the fault condition causes damage. This is

referred to as auto-shutdown and is covered in

Section 11.8 “Auto-shutdown Control”.

The COG can be configured to operate in phase

delayed conjunction with another PWM. The active

drive cycle is delayed from the rising event by a phase

delay timer. Phase delay is covered in more detail in

Section 11.7 “Phase Delay”.

A typical operating waveform, with phase delay and

dead band, generated from a single CCP1 input is

shown in Figure 11-3.

11.2

Clock Sources

The COG clock is used as the reference clock to the

various timers in the peripheral. Timers that use the

COG clock include:

• Rising and falling dead-band time

• Rising and falling blanking time

• Rising event phase delay

Clock sources available for selection include:

•8 MHz HFINTOSC

• Instruction clock (Fosc/4)

• System clock (Fosc)

The clock source is selected with the GxCS<1:0> bits

of the COGxCON0 register (Register 11-1).

11.3

Selectable Event Sources

The COG uses two independently selectable event

sources to generate the complementary waveform:

• Rising edge source

• Falling edge source

The rising edge source is selected with the GxRS<2:0>

bits and the falling edge source is selected with the

GxFS<2:0> bits. Selection control bits for both sources

are located in the COGxCON1 register (Register 11-2).

11.3.1

RISING EDGE EVENT

The rising edge event starts the PWM output active duty

cycle period. The rising edge event is the low-to-high

transition of the selected rising edge source. When the

phase delay and rising edge dead-band time values are

zero, the rising event output starts immediately.

Otherwise, the rising event output is delayed. The rising

event output causes all the following actions:

• Clear COGxOUT1.

• Start rising edge blanking counter (if enabled).

• Start rising edge dead-band counter (if enabled

and after phase delay, if that also is enabled).

• Set COGxOUT0 output after dead-band counter

expires.

11.3.2

FALLING EDGE EVENT

The falling edge event terminates the PWM output active

duty cycle period. The falling edge event is the

high-to-low transition of the selected falling edge source.

When the falling edge dead-band time value is zero, the

falling event output starts immediately. Otherwise, the

rising event output is delayed. The falling edge event

output causes all the following actions:

• Clear COGxOUT0.

• Start rising edge event input blanking (if enabled).

• Start falling edge dead-band counter (if enabled).

• Set COGxOUT1 output after dead-band counter

expires.

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