The LM4549B device is an audio codec for PC systems which is fully compliant with the
PC99 and performs the analog intensive functions of the AC ’97 Rev 2.1 architecture. Using 18-bit
sigma-delta ADCs and DACs, the LM4549B provides 90 dB of dynamic range.
The LM4549B 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 LM4549B supports Texas Instrument’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 LM4549B suitable for non-PC codec applications.
The LM4549B features the ability to connect several codecs together using the Extended AC
Link configuration of one dedicated serial data signal to the Controller per codec. LM4549B systems
support up to 8 simultaneous channels of streaming data on Input Frames (Codec to Controller) while
Output Frames (Controller to Codec) carry 2 streams to multiple codecs. The LM4549B may also be
used in systems with the Texas Instruments LM4550B to support up to 6 simultaneous channels of
streaming data on Output Frames.
The AC ’97 architecture separates the analog and digital functions of the PC audio system
allowing both for system design flexibility and increased performance.
