LM4540

AC ’97 Codec with National 3D Sound

General Description

The LM4540 is an audio codec for PC systems which per-

forms the analog-intensive function of the Analog Codec ’97

Rev 1.03 architecture. Using 18-Bit

Σ∆ A/D and D/A convert-

ers, the LM4540 provides 90dB of dynamic range.

The LM4540 was designed specifically to provide a high

quality audio path and provide all analog functionality in a PC

audio system. It features full duplex stereo A/D’s and D/A’s

and an analog mixer with 2 stereo and 3 mono inputs, each

of which has separate gain, attenuation and mute control. In

addition, the LM4540 provides National’s 3D Sound stereo

enhancement technology.

The LM4540 features AC-Link, a synchronous, fixed rate se-

rial bus for connection to the digital AC ’97 Controller. The

separation of the analog and digital functions of the AC ’97

architecture allows for system design flexibility and in-

creased overall performance.

Key Specifications

n Analog Mixer Dynamic Range

95dB (typ)

n D/A Dynamic Range

89dB (typ)

n A/D Dynamic Range

90dB (typ)

Features

n Audio Codec ’97 compliant

n Stereo 18-Bit

Σ∆ A/D’s and D/A’s with 128X

oversampling

n National’s 3D Sound circuitry

n Power management support

n Digital Interface 3V and 5V compliant

Applications

n PC Audio Systems Requiring Only 2 Stereo Inputs (CD,

Line) and 3 Mono Inputs (Mic, Phone, PC Beep)

Block Diagram

DS100906-1

FIGURE 1. LM4540 Block Diagram

February 1999

© 1999 National Semiconductor Corporation

DS100906

www.national.com