OPTION_REG datasheet(141/222 Pages) MICROCHIP

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DS22331A-page 141

MCP19111

26.0

PWM MODULE

The CCP module implemented on the MCP19111 is a

modified version of the CCP module found in standard

mid-range microcontrollers. In the MCP19111, the

PWM module is used to generate the system clock or

system oscillator. This system clock will control the

MCP19111 switching frequency, as well as set the

maximum allowable duty cycle. The PWM module

does not continuously adjust the duty cycle to control

the output voltage. This is accomplished by the analog

control loop and associated circuitry.

26.1

Standard Pulse-Width Modulation

(PWM) Mode

The PWM module output signal is used to set the

operating

switching

frequency

and

maximum

allowable duty cycle of the MCP19111. The actual duty

cycle on the HDRV and LDRV is controlled by the

analog PWM control loop. However, this duty cycle

cannot be greater than the value in the PWMRL

There are two modes of operation that concern the

system

clock

PWM

signal.

These

modes

are

stand-alone

(non-frequency

synchronization)

and

frequency synchronization.

26.1.1

STAND-ALONE (NON-FREQUENCY

SYNCHRONIZATION) MODE

When the MCP19111 is running stand-alone, the PWM

signal functions as the system clock. It is operating at

the

programmed

switching

frequency

with

programmed maximum duty cycle (DCLOCK). The

programmed maximum duty cycle is not adjusted on a

cycle-by-cycle basis to control the MCP19111 system

output. The required duty cycle (DBUCK) to control the

output is adjusted by the MCP19111 analog control

loop and associated circuitry. DCLOCK does, however,

set the maximum allowable DBUCK.

EQUATION 26-1:

26.1.2

SWITCHING FREQUENCY

SYNCHRONIZATION MODE

The MCP19111 can be programmed to be a switching

frequency MASTER or SLAVE device. The MASTER

device functions as described in Section 26.1.1

“Stand-Alone

(Non-Frequency

Synchronization)

Mode” with the exception of the system clock also

being applied to GPA1.

A SLAVE device will receive the MASTER system

clock on GPA1. This MASTER system clock will be

OR’ed with the output of the TIMER2 module. This

OR’ed signal will latch PWMRL into PWMRH and

PWMPHL into PWMPHH.

Figure 26-1 shows a simplified block diagram of the

CCP module in PWM mode.

The PWMPHL register allows for a phase shift to be

added to the SLAVE system clock.

It is desired to have the MCP19111 SLAVE devices

system clock start point shifted by a programmed

amount from the MASTER system clock. This SLAVE

phase shift is specified by writing to the PWMPHL reg-

ister. The SLAVE phase shift can be calculated by

using the following equation.

EQUATION 26-2:

BUCK

CLOCK

–



SLAVE PHASE SHIFT=PWMPHL•TOSC•(T2 PRESCALE VALUE)

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