LM4665

Filterless High Efficiency 1W Switching Audio Amplifier

General Description

The LM4665 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

LM4665 processes analog inputs with a delta-sigma modu-

lation technique that lowers output noise and THD when

compared to conventional pulse width modulators.

The LM4665 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 400mW with

less than 2%THD+N.

The LM4665 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 75%, reaching

80% at 400mW output power.

The LM4665 features a low-power consumption shutdown

mode. Shutdown may be enabled by either a logic high or

low depending on the mode selection. Connecting the Shut-

down Mode pin to either V

the Shutdown pin to be driven in a likewise manner to

activate shutdown.

The LM4665 has fixed selectable gain of either 6dB or 12dB.

The LM4665 has short circuit protection against a short from

the outputs to V

Key Specifications

Ω transducer

75%(typ)

Ω transducer

80%(typ)

3mA(typ)

2.7V to 5.5V

2.7V to 3.8V

Features

n

No output filter required for inductive transducers

n

Selectable gain of 6dB (2V/V) or 12dB (4V/V)

n

Very fast turn on time: 5ms (typ)

n

User selectable shutdown High or Low logic level

n

Minimum external components

n

"Click and pop" suppression circuitry

n

Micro-power shutdown mode

n

Short circuit protection

n

micro SMD, LLP, and MSOP packages (no heat sink

required)

Applications

n

Mobile phones

n

PDAs

n

Portable electronic devices

Typical Application

20027001

FIGURE 1. Typical Audio Amplifier Application Circuit

December 2002

© 2002 National Semiconductor Corporation

DS200270

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