LM4550 AC ’97 Rev 2.1 Multi-Channel Audio Codec with Stereo Headphone Amplifier, Sample
Rate Conversion and National 3D Sound
December 2002
LM4550
AC ’97 Rev 2.1 Multi-Channel Audio Codec with Stereo
Headphone Amplifier, Sample Rate Conversion and
National 3D Sound
General Description
The LM4550 is an audio codec for PC systems which is fully
PC99 compliant and performs the analog intensive functions
of the AC97 Rev2.1 architecture. Using 18-bit Sigma-Delta
A/D’s and D/A’s, the LM4550 provides 90 dB of Dynamic
Range.
The LM4550 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 4 stereo and 3 mono inputs, each
of which has separate gain, attenuation and mute control.
The LM4550 provides a stereo headphone amplifier with an
independent gain control and also supports National’s 3D
Sound stereo enhancement and variable sample rate con-
version. The sample rate for the A/D and D/A can be pro-
grammed separately with a resolution of 1 Hz to convert any
rate between 4 kHz–48 kHz.
The LM4550 features the ability to connect several codecs
together in a system to provide up to six channels for sur-
round sound applications. Multiple codec systems can be
built using the standard AC-Link format of one serial data
stream per codec, or using a unique National Semiconductor
feature for chaining codecs together. This chain feature re-
quires only a single data stream to the controller.
The AC97 architecture separates the analog and digital func-
tions of the PC audio system allowing both for system design
flexibility and increased performance.
Key Specifications
n
n
n
n
Analog Mixer Dynamic Range
D/A Dynamic Range
A/D Dynamic Range
Headphone Amp THD+N at 50 mW
into 32Ω
97dB
89dB
90dB
0.02%
(typ)
(typ)
(typ)
(typ)
Features
n
AC’97 Rev 2.1 compliant
n
Several LM4550s can be combined together for up to 6
channel operation
n
Unique National chaining function allows multiple codecs
to be connected serially and use only a single controller
SDATA_IN pin
n
High quality Sample Rate Conversion (SRC) from 4 kHz
to 48 kHz in 1 Hz increments.
n
Stereo headphone amp with separate gain control
n
National’s 3D Sound circuitry
n
External Amplifier Power Down (EAPD) control from
codec
n
PC-Beep passthrough to Line Out while reset is held
active low
n
Digital 3.3V and 5V compliant
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
2, 4, or 6 channel systems
© 2002 National Semiconductor Corporation
DS100972
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
