The LM4550B device 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 TIs 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 from 4 kHz to 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 (that is, of one serial data signal to the controller per
codec) or using a unique TI 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.