LM4546

AC ’97 Rev 2 Codec with Sample Rate Conversion and

National 3D Sound

General Description

The LM4546 is an audio codec for PC systems which is fully

PC98 compliant and performs the analog intensive functions

of the AC97 Rev 2 architecture. Using 18-bit Sigma-Delta

A/D’s and D/A’s, the LM4546 provides 90dB of Dynamic

Range.

The LM4546 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.

The LM4546 also provides National’s 3D Sound stereo en-

hancement.

The LM4546 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 Rev 2 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 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

DS100985-1

FIGURE 1. LM4546 Block Diagram

February 1999

© 1999 National Semiconductor Corporation

DS100985

www.national.com