To improve sound quality, reduce power demands and lower audio subsystem costs, semiconductor giant Texas Instruments Inc. has developed what it claims is the industry's first digital-input, 20-Watt stereo Class-D speaker amplifier with closed loop feedback. According to Mike Firth, TI’s productline marketing manager, closed loop architecture produces a richer, more accurate sound and lower system cost by relaxing power supply performance requirements.

“Industrial design and increasingly smaller form factors are becoming standard in the HDTV market, placing increasing pressure on manufacturers," noted Firth. "TI is addressing these form factor challenges with innovative products like the TAS5706, which provides a cost efficient solution that delivers high quality audio in slim designs."

Improving audio performance, the closed loop architecture enables the audio subsystem to have greater control over the speaker, reproducing a tighter, more accurate sound, with improved bass response. In addition, the closed loop architecture provides superior power supply rejection ratio (PSRR), which reduces power supply noise coupling into the audio band. Better noise immunity allows engineers to design lower-cost power supplies. In fact, for LCD-TVs, a TAS5706 audio amplifier can be powered off the existing +24 V backlight power supply, making a dedicated power rail for the audio subsystem unnecessary.

Other sound enhancements are made possible by the on-chip audio processing capabilities of the TAS5706, including dynamic range compression (DRC), a dedicated subwoofer channel for 2.1 applications, and speaker equalization (EQ). Speaker EQ adjusts the audio to compensate for low-quality speakers or for sub-optimal speaker placement and size in thin form factors.

Plus, it provides highly flexible output configurations - 2-Channel bridged outputs (20 W x 2), 4-Channel single-ended outputs (10 W x 4) and 2-Channel single-ended + 1-Channel bridged (2.1)- that allow manufacturers to use a single platform across multiple products. Stereo, quad and 2.1 output configurations are supported along with PWM headphone and subwoofer outputs, according to TI.

In addition to versatile outputs, TI's PurePath Studio graphical development environment reduces development time and makes programming simple. For example, speaker EQ coefficients are automatically calculated by simply dragging points on the speaker response curves. Evaluation modules, application notes and other technical documents are available to facilitate rapid design cycles, said the supplier.

In essence, the TAS5706 is a slave-only device receiving all clocks from external sources. It operates at a 384 kHz switching rate for 32-, 48-, 96- and 192-kHz data, and at a 352.8 kHz switching rate for 44.1-, 88.2- and 176.4-kHz data. The 8X oversampling combined with the fourth-order noise shaper provides a flat noise floor and excellent dynamic range from 20 Hz to 20 kHz, TI said. The TAS5706 is implemented in TI’s fifth generation BiCMOS process. Available in 10 mm x 10 mm QFP, SMT package, it is priced at $5.46 in 100-piece quantities.

www.ti.com