Datasheet

 2011 Microchip Technology Inc. Preliminary DS41576B-page 85
PIC12F752/HV752
11.0 COMPLEMENTARY OUTPUT
GENERATOR (COG) MODULE
The primary purpose of the Complementary Output
Generator (COG) is to convert a single output PWM sig-
nal into a two output complementary PWM signal. The
COG can also convert two separate input events into a
single or complementary PWM output.
The COG PWM frequency and duty cycle are deter-
mined by a rising event input and a falling event input.
The rising event and falling event may be the same
source. Sources may be synchronous or asynchronous
to the COG_clock.
The rate at which the rising event occurs determines
the PWM frequency. The time from the rising event
input to the falling event input determines the duty
cycle.
A selectable clock input is used to generate the phase
delay, blanking and dead-band times.
A simplified block diagram of the COG is shown in
Figure 11-1.
The COG module has the following features:
• Selectable clock source
• Selectable rising event source
• Selectable falling event source
• Selectable edge or level event sensitivity
• Independent output enables
• Independent output polarity selection
•Phase delay
• Dead-band control with independent rising and
falling event dead-band times
• Blanking control with independent rising and fall-
ing event blanking times
• Auto-shutdown control with:
- Selectable shutdown sources
- Auto-restart enable
- Auto-shutdown pin override control
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. In this case, the active drive must be ter-
minated before the Fault condition causes damage.
This is referred to as auto-shutdown and is covered in
Section 11.8 “Auto-shutdown Control”.
A feedback falling event arriving too late or not at all o
can be terminated with auto-shutdown or by using one
of the event inputs that is logically OR’d with the hard-
ware limit timer (HLT). See Section 9.0 “Hardware
Limit Timer (HLT) Module” for more information about
the HLT.
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.