M113 View Datasheet(PDF) - Unspecified

Part Name

Description

Manufacturer

M113

SERVICE MANUAL M113 (SUPER ONE-CHIP CHASSIS)

Unspecified 

TCL

M113 Chassis Service Manual

OPERATING DESCRIPTION

Regulation

The pin 3 senses the feedback current provided by the opto-coupler. During the switching phase the switch S2 is

closed and the shunt regulator is accessible by the pin 3. The shunt regulator voltage is typically 5V. The dynamic

resistance of the shunt regulator represented by the zener diode is 20 .

The gain of the Control input is given on Figure 10 which shows the duty cycle as a function of the current injected

into the pin 3.

The maximum current sense threshold is fixed at 1V. The peak

A 4KHz filter network is inserted

between the shunt regulator and the

PWM comparator to cancel the high

frequency residual noise.

The switch S3 is closed in Stand–by

mode during the Latched Off Phase

while the switch S2 remains open. (See

section PULSED MODE DUTY

CYCLE CONTROL).

The resistor Rdpulsed (Rduty cycle

burst) has no effect on the regulation

process. This resistor is used to

determine the burst duty cycle described in the chapter “Pulsed Duty Cycle Control” on page 8.

PWM Latch

The MC44608 works in voltage mode. The on–time is controlled by the PWM comparator that compares the

oscillator sawtooth with the regulation block output.

The PWM latch is initialized by the

oscillator and is reset by the PWM

comparator or by the current sense

comparator in case of an over current.

This configuration ensures that only a

single pulse appears at the circuit

output during an oscillator cycle.

Current Sense

The inductor current is converted to a

positive voltage by inserting a ground

reference sense resistor RSense in series

with the power switch.

The maximum current sense threshold is fixed at 1V. The peak current is given by the following equation:

Ipkmax = 1/Rsense( ) (A)

In stand–by mode, this current can be lowered as due to the activation of a 200 A current source:

IpkMAX-STBY

The current sense input consists of a filter (6k , 4pF) and of a leading edge blanking. Thanks to that, this pin is not

sensitive to the power switch turn on noise and spikes and practically in most applications, no filtering network is

8

02/12/09

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