原标题：ST STA381BW平板电视2.1通路数字音频系统解决方案

　　ST公司的STA381BW是2.1通路高效数字音频系统,嵌入了数字音频处理,数字放大, FFXTM功率输出级,耳机和2Vrms线路输出,为从源到扬声器提供了所有的数字音频流,具有成本效益,低功耗和增强的声效果. STA381BW的工作电压从4.5V到26V,最大到30V,I2C控制和I2S接口,取样速率32kHz-192kHz,具有多种保护功能如短路, 热,过流和欠压保护,1Vrms立体声模拟输出,三种输出功率级配置,可驱动2x20W8欧姆负载或2x9W 4欧姆+1x20W 8欧姆负载,主要用在轻薄型平板电视和家庭娱乐系统.本文介绍了STA381BW主要特性和方框图,数字信号处理通路框图以及多种应用电路.

　　The STA381BW is an integrated solution embedding digital audio processing, digital amplification, FFXTM power output stage, headphone and 2 Vrms line outputs. It is part of the Sound Terminal® family and provides full digital audio streaming from the source to the speaker, offering cost effectiveness, low power dissipation and sound enrichment.

　　The STA381BW input section consists of a flexible digital input serial audio interface, feeding the digital processing unit, and an analog 1 Vrms input for a seamless connection with pure analog sources. The serial audio data input interface supports many formats,including the popular IIS format.

　　The STA381BW is based on an FFXTM (Fully Flexible Amplification) processor, an STMicroelectronics proprietary technology. FFXTM is the evolution of the ST ternary technology: the advanced processor is available for ternary, binary, binary differential and phase shift PWM modulation.The STA381BW embeds the ternary, binary and binary differential implementations, a subset of the full capability of the FFXTM processor. The STA381BW power section consists of four independent half-bridges. These can be configured via digital control to operate in different modes. A 2.1 channel setup can be implemented with two half-bridges (L/R) together with a single full-bridge (subwoofer).Alternatively, the 2.0 channel setup can be done with two full-bridges. When using this configuration an external amplifier for the SW channel also can be driven through the PWM output. The STA381BW is able to deliver 2 x 20 W (ternary) into an 8 load at 18 V or 2 x 9 W (binary) into a 4 load, plus 1 x 20 W (ternary) into an 8 load at 18 V. The STA381BW also provides a capless headphone out (with embedded negative charge pump), able to deliver up to 40 mW into a 32 load or, alternatively, can be configured as a 2 Vrms line output.

　　The STA381BW digital processing unit includes up to 12 programmable biquads (EQs)allowing perfect sound equalization and offering advanced noise-shaping techniques.Moreover, the coefficient range ensures a great variety of filter shapes (low/high-pass,low/high shelf, peak, notch, band-pass). The equalization engine is fully compatible with the ST speaker compensation technology embedded into the APWorkbench suite. A state-ofthe-art multi-band DRC, STCompressorTM, equalizes the system to provide active speaker protection with full audio quality preservation against sudden sound peaks. Moreover, STSpeakerSafeTM technology offers reliable speaker protection under any condition. The master clock can be from stable BICKI (64xfs, 50% duty cycle) or external XTI.

　　STA381BW主要特性:

　　■ Wide-range supply voltage

　　– 4.5 V to 26 V (operating range)

　　– 30 V (absolute maximum rating)

　　■ I2C control with selectable device address

　　■ Full IC protection embedding:

　　– Manufacturing short-circuit protection (out vs. gnd, out vs. vcc, out vs. out) Thermal protection Overcurrent protection

　　– Undervoltage protection

　　■ 1 Vrms stereo analog input

　　■ I2S interface, sampling rate 32 kHz ~ 192 kHz, with internal sampling frequency converter for fixed processing frequency

　　■ Three output power stage configurations

　　– 2.0 mode, L/R full bridges

　　2.1 mode, L/R two half-bridges, subwoofer full bridge

　　– 2.1 mode, L/R full bridges, PWM output for external subwoofer amplifier

　　■ Driving load capabilities

　　– 2 x 20 W into 8ohm ternary modulation

　　– 2 x 9 W into 4 ohm+ 1 x 20 W into 8 ohm

　　■ FFXTM 100 dB dynamic range

　　■ Fixed output PWM frequency at any input sampling frequency

　　■ Embedded RMS meter for measuring real-time loudness

　　■ Two analog outputs:

　　– Selectable headphone / line out driver with adjustable gain via external resistors

　　– Auxiliary F3XTM analog output for external driver

　　■ Headphone:

　　– Embedded negative charge pump

　　– Full capless output configuration

　　– Driving load capabilities: 40 mW into 32 ohm

　　■ Line out:

　　– 2 Vrms line output capability

　　■ Up to 12 user-programmable biquads with noise-shaping technology

　　■ Direct access to coefficients through I2C shadowing mechanism

　　■ Fixed (88.2 kHz / 96 kHz) internal processing sampling rate

　　■ Two independent DRCs configurable as a dual-band anticlipper or independent limiters/compressors (B2DRC)

　　■ Digital gain/att +48 dB to -80 dB with 0.125 dB/step resolution

　　■ Independent (fade in, fade out) soft volume update with programmable rate 48 ~ 1.5 dB/ms

　　■ Bass/treble tones control

　　■ Audio presets:15 crossover filters, 5 anticlipping modes, nighttime listening mode

　　■ STSpeakerSafeTM protection circuitry:

　　– Pre and post processing DC blocking filters

　　– Checksum engine for filter coefficients

　　– PWM fault self-diagnosis STCompressorTM dual-band DRC

　　图1.STA381BW方框图

　　图2.STA381BW处理通路,第一部分

　　图3.STA381BW处理通路,第二部分:2.1输出,单独可配置

　　图4.STA381BW处理通路,第二部分:带B2DRC的2.0输出

　　图5.STA381BW处理通路,第二部分:2.1输出配置和STCompressorTM

　　图6.STCompressorTM方框图

　　图7.STA381BW外接音频源到线路/耳机输出应用电路

　　图8.STA381BW F3X(来自SAI)源到线路/耳机输出应用电路

　　图9.STA381BW F3X辅助模拟输出电路

　　图10.STA381BW立体声模式的输出配置电路