2 MHz

Oscillator

Soft

Start

Ramp

Generator

+

-

Thermal

Shutdown

Undervoltage

Lockout

+

-

0.5V

Error

Amp

Control Logic

Driver

Current Limit

Comparator

Ref1

SW

FB

EN

PWM Comparator

GND

Bandgap

+

-

Vcomp

1.0V

Frequency

Compensation

Adjustable Version

Fixed Version

LM3674

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SNVS405G – DECEMBER 2005 – REVISED APRIL 2015

7 Detailed Description

7.1 Overview

The LM3674, a high-efficiency, step-down, DC-DC switching buck converter, delivers a constant voltage from a

single Li-Ion battery and input voltage rails from 2.7 V to 5.5 V to portable devices such as cell phones and

PDAs. Using a voltage mode architecture with synchronous rectification, the LM3674 has the ability to deliver up

to 600 mA depending on the input voltage, output voltage, ambient temperature, and the inductor chosen.

Additional features include soft-start, undervoltage protection, current overload protection, and thermal overload

required for implementation.

The part uses an internal reference voltage of 0.5 V. It is recommended to keep the part in shutdown mode until

the input voltage is 2.7 V or higher.

7.2 Functional Block Diagram

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Product Folder Links: LM3674