LM4921

Low Voltage I

Headphone Power Amplifiers and Volume Control

General Description

The LM4921 combines a 16-bit resolution stereo I

digital-to-analog converter (DAC) with a stereo headphone

audio power amplifier. It is primarily designed for demanding

applications in mobile phones and other portable communi-

cation device applications. The LM4921 features an I

serial interface for the digital audio information and a 16-bit

SPI serial interface for internal register control and commu-

nication. With AV

Ω

single-ended load to a 26mW

(THD+N) of the LM4921 will be less than 0.5%. The LM4921

also features a programmable 32-step digital volume control

accessed through an SPI interface.

Boomer audio power amplifiers were designed specifically to

provide high quality output power with a minimal amount of

external components. It is, therefore, ideally suited for mo-

bile phone and other low voltage applications where minimal

power consumption is a primary requirement.

The LM4921 features a low-power consumption shutdown

mode, and also has an internal thermal shutdown protection

mechanism.

Key Specifications

52dB (typ)

Ω

13mW (typ)

26mW (typ)

DV

DD

2.6V to 5.0V

AV

2.6V to 5.5V

1µA (typ)

Features

n

16-bit resolution stereo DAC

n

I

n

SPI serial interface (control register)

n

Volume Control (32 steps; 1.5 dB increments)

n

Up to 50mW/channel stereo headphone amplifier

n

Zero Crossing Detection for Silent Attenuation Steps

n

2.6V

n

2.6V

n

Unity-gain stable headphone amplifiers

n

Available in the 20-bump microSMD package

Applications

n

Mobile phones

n

PDAs

n

Portable electronic devices

November 2004

© 2004 National Semiconductor Corporation

DS200486

www.national.com