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LM4550BVH-LM4550BVHX-LM4550VH
AC '97 Rev 2.1 Codec with Sample Rate Conversion and National 3D Sound
LM4550 ’97 Rev 2.1 Multi-Channel Audio Codec with Stereo
Headphone Amplifier, Sample Rate Conversion and
National 3D Sound
General DescriptionThe LM4550isan audio codecforPC systems whichis fully
PC99 compliant and performsthe analog intensive functionstheAC’97 Rev2.1 architecture. Using 18-bit Sigma-Delta
ADCs and DACs, the LM4550 provides90dBof Dynamic
Range.
The LM4550 was designed specificallyto providea high
quality audio path and provideall analog functionalityinaPC
audio system.It featuresfull duplex stereo ADCs and DACs
and analog mixers with accessto4 stereo and4 mono
inputs. Each mixer input has separate gain, attenuation and
mute control and the mixers drive1 mono and2 stereo
outputs, each with attenuation and mute control. The
LM4550 providesa stereo headphone amplifieras oneofits
stereo outputs and also supports National’s3D Sound stereo
enhancement anda comprehensive sample rate conversion
capability. The sample rateforthe ADCs and DACs canbe
programmed separately witha resolutionof1Hzto convert
any rateinthe range4 kHz–48 kHz. Sample timing fromthe
ADCs and sample request timingfor the DACs are com-
pletely deterministicto ease task scheduling and application
software development. These features together withan ex-
tended temperature range also make the LM4550 suitable
for non-PC codec applications.
The LM4550 features the abilityto connect several codecs
togetherina systemto provideupto6 simultaneous chan-
nelsof streaming dataon Output Frames (Controllerto
Codec)for surround sound applications. Such systems can
also supportupto8 simultaneous channelsof streaming
dataon Input Frames (Codecto Controller). Multiple codec
systems canbe built either using the standard AC Link
configuration (i.e.of one serial data signaltothe Controller
per codec)or usinga unique National Semiconductor fea-
turefor chaining codecs together. This chain feature shares
onlya single data signalto the controller among multiple
codecs.
The AC ’97 architecture separates the analog and digital
functionsof thePC audio system allowing bothfor system
design flexibility and increased performance.
Key Specifications Analog Mixer Dynamic Range 97dB (typ) DAC Dynamic Range 89dB (typ) ADC Dynamic Range 90dB (typ) Headphone Amp THD+Nat50 mW 0.02% (typ)
into 32Ω
Features AC’97 Rev2.1 compliant High quality Sample Rate Conversion from4 kHzto48
kHzin1Hz increments Supportsupto6 DAC channel systems with multiple
LM4550sor with other National LM45xx codecs Unique National chaining function sharesa single
controller SDATA_INpin among multiple codecs Stereo headphone amp with separate gain control National’s3D Sound stereo enhancement circuitry Advanced power management support External Amplifier Power Down (EAPD) control PC Beep passthroughto Line Out during Initializationor
Cold Reset Digital 3.3V and5V supply options Extended Temperature: −40˚C≤TA≤ 85˚C
Applications DesktopPC audio systemson PCI cards, AMR cards,or
with motherboard chips sets featuringAC Link Portable PC systemsason MDC cards,or witha
chipsetor accelerator featuringAC Link General Audio Frequency Systems requiring2,4or6
DAC channels and/orupto8 ADC channels
May 2004
LM4550
’97
Rev
Multi-Channel
Audio
Codec
with
Stereo
Headphone
Amplifier
Sample
Rate
Conversion
and
National
Sound
