ST 公司的STA350BW是 2x50W 2.1通路数字音频系统，集成了数字音频处理，数字放大器控制和FFX功率输出级。输入电压5V-26V，四路输出配置，25V时能向6欧姆提供2x50W输出功率，100dB SNR和动态范围，输入取样速率在32kHz到192kHz间选择，I2C控制，数字控制增益从+42dB到-80dB，每步分辨率0.125dB。本文介绍了STA350BW主要特性，方框图，单声道并行BTL电路图，电源电路图，立体声BTL模式输出配置图以及STA350BW 2.0通路演示板电路替，输出滤波器电路图和材料清单。
STA350BW：Sound Terminal® 2.1-channel high-efficiency digital audio system
The STA350BW is an integrated solution of digital audio processing, digital amplifier control, and FFX-power output stage, thereby creating a high-power single-chip FFX® solution comprising high-quality, high-efficiency, and all-digital amplification.
The STA350BW is based on an FFX (fully flexible amplification) processor, a proprietary technology from STMicroelectronics. FFX is the evolution and the enlargement of ST’s ternary technology: the new processor can be configured to work in ternary, binary, binary differential and phase-shift PWM modulation schemes.
The STA350BW contains the ternary, binary and binary differential implementations, a subset of the full capability of the FFX processor.
The STA350BW is part of the Sound Terminal® family that provides full digital audio streaming to the speaker, offering cost effectiveness, low power dissipation and sound enrichment.
The STA350BW power section consists of four independent half-bridges. These can be configured via digital control to operate in different modes. 2.1 channels can be provided by two half-bridges and a single full-bridge, providing up to 2 x 18 W + 1 x 40 W of music output power, by using standard 4 and 8ohm speakers. Two channels can be provided by two fullbridges, providing up to 2 x 50 W of music power, by using standard 6ohm speaker or 2 x 40 W by using 8ohm speakers at 25 V. The IC can also be configured as 2.1 channels with 2 x 40 W provided by the device and external power for FFX power drive. If configured as Mono-BTL, the latter is capable of providing up to 1 x 90 W on a standard 3 ohm load or 1 x 75 W by using a 4ohm setting the supply voltage at 25 V. Please refer to the package thermal characteristics and application suggestions for more details.
Also provided in the STA350BW are a full assortment of digital processing features. This includes up to 8 programmable biquads (EQ) per channel. Special digital signal processing techniques are available in order to manage low-frequency quantization noise in case of very low frequency cutoff filter thresholds. The coefficient range -4..4 allows the easy implementation of high shelf filters. Available presets allow the advantage of earlier time-tomarket by substantially reducing the amount of software development needed for certain functions. This includes audio preset volume loudness, preset volume curves and preset EQ settings. There are also new advanced AM radio interference reduction modes. Dual-band DRC dynamically equalizes the system to provide speaker linear frequency response regardless of output power level. This feature independently processes the two bands, controlling dynamically the output power level in each band and so providing better sound clarity.
The serial audio data input interface accepts all possible formats, including the popular I2S format. Three channels of FFX processing are provided. This high-quality conversion from PCM audio to FFX PWM switching waveform provides over 100 dB SNR and dynamic range.

STA350BW主要特性：
■ Wide-range supply voltage
– 5 V to 26 V (operating range)
– 30 V (absolute maximum rating)
■ Four power output configurations(a)
– 2 channels of ternary PWM (stereo mode) (2 x 50 W into 6 ohm at 25 V)
– 3 channels - left, right using binary and LFE using ternary PWM (2.1 mode) (2 x 18 W + 1 x 40W into 2 x 4 ohm , 1 x 8 ohmat 25 V)
– 2 channels of ternary PWM (2 x 50 W) + stereo lineout ternary
– 1 channel of ternary PWM as Mono BTL (1 x 90 W into 3 ohmat 24.5V)
■ FFX®100 dB SNR and Dynamic Range
■ Selectable 32 to 192 kHz input sample rates
■ I2C control with selectable device address
■ Digital gain/attenuation +42 dB to -80 dB with 0.125 dB/step resolution
■ Soft-volume update with programmable ratio
■ Individual channel and master gain/attenuation
■Two independent DRCs configurable as a dual-band anti-clipper (B2DRC) or independent limiters/compressors
■ EQ-DRC for DRC based on filtered signals
■ Dedicated LFE processing for bass boosting with 0.125 dB/step resolution
■ Audio presets:
– 15 preset crossover filters
– 5 preset anti-clipping modes
– Preset nighttime listening mode
■ Individual channel and master soft/hard mute
■ Independent channel volume and DSP bypass
■ Automatic zero-detect mute
■ Automatic invalid input-detect mute
■ I2S input data interface
■ Input and output channel mapping
■ Up to 8 user-programmable biquads per channel
■ 3 coefficient banks for EQ presets storing with fast recall via I2C interface
■ Extended coefficient dynamic up to -4..4 for easy implementation of high shelf filters
■ Bass/treble tones and de-emphasis control
■ Selectable high-pass filter for DC blocking
■ Advanced AM interference frequency switching and noise suppression modes
■ Selectable high- or low-bandwidth noise-shaping topologies
■ Selectable clock input ratio
■ 96 kHz internal processing sample rate with quantization error noise shaping for very low cutoff frequency filters
■ Thermal overload and short-circuit protection embedded
■ Video apps: 576 x Fs input mode supported
■ Fully compatible with STA339BW and STA339BWS

图1。STA350BW方框图

图2。STA350BW单声道并行BTL电路图

图3。STA350BW电源电路图

图4。STA350BW立体声BTL模式输出配置图

STA350BW 2.0通路演示板
The STA350BW demonstration board is specifically configured for 2.0 BTL channels,releasing up to 2 x 50 W into 6 ohm of power output at 25 V of supply voltage using reduced components. It is a complete solution for the digital audio power amplifier.

图5。STA350BW 2.0通路演示板外形图

图6。STA350BW 测试连接框图

图7。STA350BW 2.0通路演示板电路图

图8。STA350BW 输出滤波器电路图
STA350BW 2.0通路演示板材料清单（BOM）：

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