LM3101 datasheet(6/20 Pages) NSC

6 / 20 page

Typical Performance Characteristics (Continued)

Step Response

Error Amplifier

Frequency Response

Open Loop

Error Amplifier

TLH11436 – 4

Pin-by-Pin Description

Symbol

Function

Description

1RT

Frequency Setting

Connecting a resistor RT between this pin and ground programs the frequency

Resistor

from 50 kHz to 1 MHzby the following equation

RT e 025(FO 20 10b12)

F Hz X

RT also sets the internal bias current which affects the operation of several sub-

circuits within the IC

Mode Control

For voltage mode operation connect a resistor RMC from this pin to the supply

voltage For current mode operation this pin is tied to ground via resistor RMC A

current is sourced from the pin through the resistor such that it sets the slope of the

compensating ramp ICOMP according to the equation

ICOMP DT e 24 103 (RT RMC)

A ms X

SFST

Soft-Start Control

A series resistor-capacitor network tied from this pin to ground provides Soft-Start

capability The current charging the capacitor is

ISFST e 045RT

A V X

Leave this pin open if it is not used

SYNC

Synchronization

An external negative pulse fed to this input will synchronize the internal oscillator

Signal Input

The frequency range of the external signal should be between 11 to 15 times the

free-running frequency Connect this pin to ground if it is not used

5RSC

Short Circuit Frequency

A resistor RSC connected from this pin to the regulator output determines the

Shift Control

oscillator frequency during a short circuit by the formula

RSC e 009 (0267RT)-FSC 20 b12

F Hz X

or alternately

FSC e (120 10b12) (0267RT) - (009RSC)

F Hz X

The recommended minimum ratio of short circuit frequency to oscillator frequency is

one-third (nominal)

CMI

Current Mode Input

An analog voltage signal proportional to the transformer primary current fed to this

input results in current mode operation Connect this pin directly to ground if

selecting voltage mode operation

GND

Ground

8VOUT

Output

Output pin It produces a PWM pulse train that is fed back to the primary side of the

regulator via a pulse transformer

9VS

Supply Voltage

Supply voltage

Crowbar Output

This pin delivers a current when an overvoltage condition occurs on the output It can

Driver

be used to fire an external SCR to crowbar the output Leave the pin open if not

used

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