LM4550B AC ’97 Rev 2.1 Multi-Channel Audio Codec with Stereo Headphone Amplifier, Sample
Rate Conversion and National 3D Sound
September 2005
LM4550B
AC ’97 Rev 2.1 Multi-Channel Audio Codec with Stereo
Headphone Amplifier, Sample Rate Conversion and
National 3D Sound
General Description
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 con-
version 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 appli-
cation 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 chan-
nels 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 fea-
ture 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.
Key Specifications
n
n
n
n
Analog Mixer Dynamic Range
DAC Dynamic Range
ADC Dynamic Range
Headphone Amp THD+N at 50 mW
into 32Ω
97 dB
89 dB
90 dB
0.02%
(typ)
(typ)
(typ)
(typ)
Features
n
AC ’97 Rev 2.1 compliant
n
High quality Sample Rate Conversion from 4 kHz to 48
kHz in 1 Hz increments
n
Supports up to 6 DAC channel systems with multiple
LM4550Bs or with other National LM45xx codecs
n
Unique National chaining function shares a single
controller SDATA_IN pin among multiple codecs
n
Stereo headphone amp with separate gain control
n
National’s 3D Sound stereo enhancement circuitry
n
Advanced power management support
n
External Amplifier Power Down (EAPD) control
n
PC Beep passthrough to Line Out during Initialization or
Cold Reset
n
Digital 3.3V and 5V supply options
n
Extended Temperature: −40˚C
≤
T
A
≤
85˚C
Applications
n
Desktop PC audio systems on PCI cards, AMR cards, or
with motherboard chips sets featuring AC Link
n
Portable PC systems as on MDC cards, or with a
chipset or accelerator featuring AC Link
n
General Audio Frequency Systems requiring 2, 4 or 6
DAC channels and/or up to 8 ADC channels
n
Automotive telematics
© 2005 National Semiconductor Corporation
DS201237
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
