描述 Description

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 programmed separately with a resolution of 1 Hz to convert any rate between 4 kHz–48 kHz.Key Specifications
Analog Mixer Dynamic Range 97dB (typ)
D/A Dynamic Range 89dB (typ)
A/D Dynamic Range 90dB (typ)
Headphone Amp THD+N at 50 mW 0.02% (typ) into 32?

特性 Features

AC’97 Rev 2.1 compliant
Several LM4550s can be combined together for up to 6 channel operation
Unique National chaining function allows multiple codecs to be connected serially and use only a single controller SDATA_IN pin
High quality Sample Rate Conversion (SRC) from 4 kHz to 48 kHz in 1 Hz increments.
Stereo headphone amp with separate gain control
National’s 3D Sound circuitry
External Amplifier Power Down (EAPD) control from codec
PC-Beep passthrough to Line Out while reset is held active low
Digital 3.3V and 5V compliantApplications
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
2, 4, or 6 channel systems