LM4548

AC ’97 Rev 2 Codec with Sample Rate Conversion and

National 3D Sound

General Description

The LM4548 is an audio codec for PC systems which is fully

PC98 compliant and performs the analog intensive functions

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

A/D’s and D/A’s, the LM4548 provides 90dB of Dynamic

Range.

The LM4548 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 LM4548 also provides the additional True Line-Level

output and National’s 3D Sound stereo enhancement.

The LM4548 supports variable sample rate conversion as

defined in the AC97 Rev2 specification. The sample rate for

the A/D and D/A can be programmed separately to convert

any rate between 4kHz - 48kHz with a resolution of 1Hz. The

AC97 architecture separates the analog and digital functions

of the PC audio system allowing both for system design flex-

ibility 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 Rev2 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 True Line Level Output with volume control in addition to

standard Line Out

n Advanced power management support

n Digital 3V and 5V compliant

Applications

n Desktop PC Audio Systems

n Portable PC Systems

n Mobile PC Systems

Block Diagram

DS100987-1

FIGURE 1. LM4548 Block Diagram

February 1999

© 1999 National Semiconductor Corporation

DS100987

www.national.com