LM4550B

The LM4550B is an audio codec for PC systems which is fully PC99 compliant and performs the analog intensive functions of the AC '97 Rev 2.1 architecture. Using 18-bit Sigma-Delta ADCs and DACs, the LM4550B provides 90 dB of Dynamic Range. The LM4550B 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 ADCs and DACs and analog mixers with access to 4 stereo and 4 mono inputs.

Each mixer input has separate gain, attenuation and mute control and the mixers drive 1 mono and 2 stereo outputs, each with attenuation and mute control. The LM4550B provides a stereo headphone amplifier as one of its stereo outputs and also supports National's 3D Sound stereo enhancement and a comprehensive sample rate conversion capability.

The sample rate for the ADCs and DACs can be programmed separately with a resolution of 1 Hz to convert any rate in the range 4 kHz 48 kHz. Sample timing from the ADCs and sample request timing for the DACs are completely deterministic to ease task scheduling and application software development.

These features together with an extended temperature range also make the LM4550B suitable for non-PC codec applications. The LM4550B features the ability to connect several codecs together in a system to provide up to 6 simultaneous channels of streaming data on Output Frames (Controller to Codec) for surround sound applications. Such systems can also support up to 8 simultaneous channels of streaming data on Input Frames (Codec to Controller). Multiple codec systems can be built either using the standard AC Link configuration (i.e. of one serial data signal to the Controller per codec) or using a unique National Semiconductor feature for chaining codecs together.

This chain feature shares only a single data signal to the controller among multiple codecs. The AC '97 architecture separates the analog and digital functions of the PC audio system allowing both for system design flexibility and increased performance.