IR3637SPBF datasheet(4/21 Pages) IRF

4 / 21 page

Rev.1.1

06/16/05

IR3637SPBF

www.irf.com

BLOCK DIAGRAM

Figure 2 - Simplified block diagram of the IR3637.

25uA

64uA Max

POR

Oscillator

Error Amp

Error Comp

Reset Dom

POR

0.4V

FbLo Comp

HDrv

Vcc

LDrv

Gnd

Vcc

4.2V

3.3V

Bias

Generator

0.8V

POR

SS/SD

Fb 1

Comp 7

25K

0.8V

Short-Circuit Protection

The output is protected against the short-circuit. The

IR3637 protects the circuit for shorted output by sens-

ing the output voltage (through the external resistor di-

vider). The IR3637 shuts down the PWM signals, when

the output voltage drops below 0.4V.

Under-Voltage Lockout

The under-voltage lockout circuit assures that the

MOSFET driver outputs remain in the off state whenever

the supply voltage drops below set parameters. Lockout

occurs if Vc or Vcc fall below 3.3V and 4.2V respec-

tively. Normal operation resumes once Vc and Vcc rise

above the set values.

Shutdown

The converter can be shutdown by pulling the soft-start

pin below 0.4V. This can be easily done by using an

external small signal transistor. During shutdown the con-

trol MOSFET driver is turned off and the synchronous

MOSFET driver is turned on.

Introduction

The IR3637 is a fixed frequency, voltage mode synchro-

nous controller and consists of a precision reference

voltage, an error amplifier, an internal oscillator, a PWM

comparator, 0.5A peak gate driver, soft-start and shut-

down circuits (see Block Diagram).

The output voltage of the synchronous converter is set

and controlled by the output of the error amplifier; this is

the amplified error signal from the sensed output voltage

and the reference voltage.

This voltage is compared to a fixed frequency linear

sawtooth ramp and generates fixed frequency pulses of

variable duty-cycle, which drives the two N-channel ex-

ternal MOSFETs.The timing of the IC is provided through

an internal oscillator circuit which uses on-chip capaci-

tor to set the oscillation frequency to 400kHz.

THEORY OF OPERATION

IR3637SPBF Datasheet(PDF) 4 Page - International Rectifier

IR3637SPBF Datasheet(HTML) 4 Page - International Rectifier

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

Datasheet Download

Link URL