LM4664

Filterless High Efficiency 1.1W Switching Audio

Amplifier

General Description

The LM4664 is a fully integrated single-supply high efficiency

switching audio amplifier. It features an innovative modulator

that eliminates the LC output filter used with typical switching

amplifiers. Eliminating the output filter reduces parts count,

simplifies circuit design, and reduces board area. The

LM4664 processes analog inputs with a delta-sigma modu-

lation technique that lowers output noise and THD when

compared to conventional pulse width modulators.

The LM4664 is designed to meet the demands of mobile

phones and other portable communication devices. Operat-

ing on a single 3V supply, it is capable of driving 8

Ω trans-

ducer loads at a continuous average output of 425mW with

less than 1%THD+N. Its flexible power supply requirements

allow operation from 2.7V to 5.5V.

The LM4664 has high efficiency with an 8

Ω transducer load

compared to a typical Class AB amplifier. With a 3V supply,

the IC’s efficiency for a 100mW power level is 74%, reaching

84% at 425mW output power.

The LM4664 features a low-power consumption shutdown

mode. Shutdown may be enabled by driving the Shutdown

pin to a logic low (GND).

The LM4664 has fixed selectable gain of either 6dB or 12dB.

The LM4664 has short circuit protection against a short from

the outputs to V

Key Specifications

Ω transducer 74% (typ)

Ω transducer 84% (typ)

Ω transducer

86% (typ)

3.5mA (typ)

0.4µA (typ)

2.7V to 5.5V

Features

n

No output filter required for inductive transducers

n

Selectable gain of 6dB or 12dB

n

Very fast turn on time: 7ms (typ)

n

Minimum external components

n

"Click and pop" suppression circuitry

n

Micro-power shutdown mode

n

Short circuit protection

n

Available in space-saving micro SMD package

Applications

n

Mobile phones

n

PDAs

n

Portable electronic devices

Typical Application

200960G5

FIGURE 1. Typical Audio Amplifier Application Circuit

March 2004

© 2004 National Semiconductor Corporation

DS200960

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