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Features
AC '97 Rev 2.1 compliant
High quality Sample Rate Conversion from
4 kHz to 48 kHz in 1 Hz increments
Multiple codec support
True Line Level Output with separate gain control
National's 3D Sound stereo enhancement circuitry
Advanced power management support
External Amplifier Power Down (EAPD) control
PC-Beep passthrough to Line Out during Initialization or Cold Reset
Digital 3.3V and 5V supply options
Extended Temperature: −40°C
≤ TA
≤ 85°C
Description The LM4549A 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 LM4549A provides 90 dB of Dynamic Range.
The LM4549A 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 LM4549A supports National'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 LM4549A suitable
for non-PC codec applications.
The LM4549A 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. LM4549A 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 LM4549A
may also be used in systems with the National LM4550 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.
Key Specification
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Analog Mixer Dynamic Range
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97 dB (typ)
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DAC Dynamic Range
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89 dB (typ)
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ADC Dynamic Range
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90 dB (typ)
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Applications
Desktop PC audio systems on PCI cards, AMR cards, or with motherboard chips sets featuring AC Link
Portable PC systems as on MDC cards, or with a chipset or accelerator featuring AC Link
General and Multi-channel audio frequency systems
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