PIC16F753 datasheet(135/230 Pages) MICROCHIP

135 / 230 page

 2013-2015 Microchip Technology Inc.

DS40001709C-page 135

PIC16F753/HV753

17.0

SLOPE COMPENSATION (SC)

MODULE

The Slope Compensation (SC) module is designed to

provide the necessary slope compensation for fixed

frequency, continuous current, and current mode

switched power supplies. Slope compensation is a

necessary feature of these power supplies because it

prevents frequency instabilities at duty cycles greater

than 50%.

17.1

Theory of Operation

The SC module works by quickly discharging an internal

capacitor at the beginning of each PWM period. An

internal current sink charges this capacitor at a program-

mable rate. As the capacitor charges, the capacitor volt-

age is subtracted from the reference voltage, producing

a linear voltage decay at the required rate. The current

reference voltage can be supplied by either an I/O pin or

by the buffered output of the FVR peripheral. The FVR

module provides either a fixed voltage or a programma-

ble DAC output. The Reset source can be derived from

either the COG output or the synchronized output of

either comparator. Additionally, the Reset source can be

inverted before triggering the Reset. The slope voltage

can be sent to either comparator or the op amp.

The core of the SC module is:

• an on-chip capacitor in series with the voltage

source,

• a shorting switch across the capacitor, and

• a calibrated current sink.

A one-shot pulse generator ensures that the switch is

closed long enough to completely discharge the

capacitor. This typically takes 50 ns.

FIGURE 17-1:

SIMPLIFIED SC MODULE BLOCK DIAGRAM

One Shot

SCxISET * 0.75/15 + 0.2V/µS

SCxISET + 1.0V/µS

SLPCIN

SCxINS

FVR_buffer1

SCxPOL

COG1_output0

COG1_output1

C1OUT_sync

C2OUT_sync

SCxTSS<1:0>

SCxISET<3:0>

SLOPE_output

SCxRNG

peripherals

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