Atmel AT73C209 MP3混合音频方案

Atmel 公司的AT73C209用于低成本 音乐播放器的混合模式模拟电路，集成了立体声音频DAC和功率管理器件，非常适合以电池为能源的设备如walkman 格式或海量存储USB格式的MP3播放器。立体声DAC部分具有可编程特性和93 dB的动态范围，能向32欧姆提供20mW的立体声输出功率。而功率管理部分的输入电压从0.9V到1.8V，具有动态功率管理特性和非常低的静态功耗。本文介绍了AT73C209的主要性能，功能方框图，应用电路及其所用元器件列表；同时还介绍了AT73C209-EK2评估板的主要性能及其主电路图，电平转移电路图和S/PDIF 接口电路图。

Atmel Introduces Mixed Mode Analog Companion IC for Low-cost Music Players
AT73C209 Audio and Power Management
The AT73C209 is a fully integrated, low cost, combined Stereo Audio DAC and Power Management Circuit targeted for battery powered devices such as MP3 players in "walkman" format or "mass storage" USB format. The stereo DAC section is a complete high performance, stereo audio digital-to-analog converter delivering a 93 dB dynamic range. It comprises a multibit sigma-delta modulator with dither, continuous time analog filters and analog output drive circuitry. This architecture provides a high insensitivity to clock jitter. The digital interpolation filter increases the sample rate by a factor of 8, using 3 linear phase half-band cascaded filters, followed by a first order SINC interpolator with a sample-rate factor of 8. This filter eliminates the images of baseband audio, retaining only the image at 64x the input sample rate, which is eliminated by the analog post filter. Optionally, a dither signal can be added that reduces possible noise tones at the output. However, the use of a multibit sigma-delta modulator provides extremely low noise tone energy. Master clock is 256 or 384 times the input data rate, allowing multiple choice of input data rate up to 48 kHz, including standard audio rates of 48, 44.1, 32, 16 and 8 kHz. The DAC section also comprises volume and mute control and can be simultaneously played back directly on the line outputs and through a 32-Ohms stereo headset.

The 32-Ohms pair of stereo-headset drivers also includes a LINEL and LINER channel-mixer pair of stereo inputs. Every DAC can be powered down separately via internal register control. Each single left or right DAC can be directed in MONO mode to the stereo headset and line outputs while the other is set in off mode. In addition, a microphone preamplifier with a microphone bias switch is integrated, reducing external ICs and saving board space. The volume, mute, power down, de-emphasis controls and 16-bit, 18-bit and 20-bit audio for-mats are digitally programmable via a 4-wire SPI bus and the digital audio data is provided through a multi-format I2S interface. The Power Management section can tolerate several types of input supply, such as: • Battery: voltage is converted to 3.3V via a DC/DC step up converter using 1 external inductor, 1 schottky diode and a capacitor. – Disposable AA or AAA size – coin cell size, 1 cell, as low as 0.9V for alkaline • USB: 5V VBUS supply from a USB connector or a Lithium-Ion battery The Power Management section also includes a set of low dropout (LDO) voltage regulators with different voltages to supply specific chip and analog requirements: • LDO1 is designed to drive up to 150 mA from a USB port with 9-step programmable output voltages: 2.7V, 2.8V, 2.9V, 3.0V, 3.1V, 3.2V, 3.3V, 3.4V, 3.5V. Default voltage is 3.4V and represents the initial output voltage of LDO1 at start up. When RSTB is activated, the external MCU can change the output voltage via the SPI serial interface. This LDO is designed to supply the complete chip when the device is connected to a USB port. • LDO2 is designed to drive up to 60 mA from LDO1 with 4-step programmable output voltages: 2.4V, 2.6V, 2.8V, 3.0V with low noise and high PSRR. Default voltage is 3.0V and represents the initial output voltage of LDO2 at start up. When RSTB is activated, the MCU can change the output voltage via the SPI serial interface. This LDO is designed to supply the internal analog section.

AT73C209主要特性：
Power Management
Supply Input from USB or 1x Disposal Battery (Alkaline, NimH, NiCd)
Input Voltage Range: 0.9V to 1.8V
2.7V/2.9V/3.1V/3.3V - 100 mA Step-Up DC/DC Converter for Main Supply
2.7V to 3.5V (100mV step) - 150 mA LDO from USB supply
2.4V to 3.0V (200mV step) - 60 mA LDO for Analog Supply
Reset Generator
SPI Interface and Internal Programming Registers
Dynamic Power Management
Very Low Quiescent Current Operation
Stereo Audio DAC
Programmable Stereo Audio DAC (16-bits, 18-bits or 20-bits)
93 dB SNR Playback Stereo Channels
32 Ohm/20 mW Stereo Headset Drivers with Master Volume and Mute Controls
Stereo Line Level Input with Volume Control/Mute and Playback through the Headset Driver
Microphone Preamplifier
Stereo, Mono and Reverse Stereo Mixer
Left/Right Speaker Short-Circuit Detection Flag
8, 11.024, 16, 22.05, 24, 32, 44.1 and 48 kHz Sampling Rates
256x or 384xFs Master Clock Frequency
I2S Serial Audio Interface
Low Power Operation
应用:
Ideally Suited to Interface with Atmel’s AT8xC51SNDxC MP3 Microcontroller
Portable Music Players, Digital Cameras, CD Players, Handheld GPS

图1.AT73C209 功能方框图



图2.采用单节电池的AT73C209应用电路

下表为AT73C209应用电路所用元件列表：




AT73C209开发评估板AT73C209-EK2
The AT73C209-EK2 is an evaluation platform intended to facilitate demonstration of the AT73C209 features
AT73C209-EK2 主要特性：
The AT73C209-EK2 provides the following features:
Power supply:
Transformer
External battery connection
USB
Serial interfaces:
Parallel port, male type (converted to SPI)
On-board resources:
Programable digital step-up DC/DC converter
2 programable LDOs
Reset Generator
Programable Stereo Audio DAC (16-bits, 18-bits or 20-bits)
93 dB SNR Playback Stereo Channels
32-Ohm/20 mW Stereo Headset Drivers with master volume and mute controls,
Stereo Line Level input with volume control/mute and playback through the headset driver
Microphone Preamplifier
Stereo, Mono and reverse Stereo mixer,
On-board buttons:
Power On
SPDIF to I2S converter reset

图3. AT73C209-EK2评估板外形图

图4. AT73C209-EK2 主电路图

图5. AT73C209-EK2 电平转移电路图

图7.AT73C209-EK2 S/PDIF 接口电路图