LM4549

AC ’97 Rev 2.1 Codec with Sample Rate Conversion and

National 3D Sound

General Description

The LM4549 is an audio codec for PC systems which is fully

PC98 compliant and performs the analog intensive functions

of the AC97 Rev2.1 architecture. Using 18-bit Sigma-Delta

A/D’s and D/A’s, the LM4549 provides 90dB of Dynamic

Range.

The LM4549 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 4 stereo and 3 mono inputs, each

of which has separate gain, attenuation and mute control.

The codec features a second Line Output known as True

Line Level Out that is identical to Line Out but with indepen-

dent volume control. The LM4549 also features National’s

3D Sound stereo enhancement and variable sample rate

conversion. The sample rate for the A/D and D/A can be pro-

grammed separately with a resolution of 1Hz to convert any

rate between 4kHz-48kHz.

The AC97 architecture separates the analog and digital func-

tions of the PC audio system allowing both for system design

flexibility and increased performance.

Key Specifications

n Analog Mixer Dynamic Range

97dB (typ)

n D/A Dynamic Range

89dB (typ)

n A/D Dynamic Range

90dB (typ)

Features

n AC’97 Rev 2.1 compliant

n National’s 3D Sound circuitry

n High quality Sample Rate Conversion (SRC) from 4kHz

to 48kHz in 1Hz increments.

n Multiple Codec Support

n External Amplifier Power Down (EAPD) control from

codec

n PC-Beep passthrough to Line Out while reset is held

active low

n True Line Level Output with volume control independent

of Line Out

n Digital 3V and 5V compliant

Applications

n Desktop PC Audio Systems on PCI cards, AMR cards,

or with motherboard chips sets featuring AC-Link

n Portable PC Systems as on MDC cards, or with a

chipset or accelerator featuring AC-Link

Block Diagram

DS101035-1

FIGURE 1. LM4549 Block Diagram

February 1999

© 1999 National Semiconductor Corporation

DS101035

www.national.com