Single-chip stereo digital amp doubles channel count

Dallas — Texas Instruments Inc. (TI), gave a boost to audio amplifier design by announcing two high-performance digital amplifier power stages. These power stages mark the industry's first single-chip solution to drive two channels of 125 W per channel, as well as the first to drive two channels at 100 W. Manufacturers of DVD receivers and audio/video (A/V) receivers will be able to continue meeting the consumer demand for higher power with TI's latest additions to its PurePath digital technologies.

The TAS5152 power stage enables a wide variety of high performance applications, including 1000 W 7.1 channel systems, while providing complete, end-to-end digital amplification. TI also offers the TAS5142 dual-channel power stage for applications requiring 100 W per channel. With an industry-leading efficiency of greater than 90 percent, signal-to-noise ratio (SNR) of up to 110 dB, and an impressive total harmonic distortion (THD) of typically less than 0.1 percent, the TAS5152 provides unparalleled performance and signal clarity while eliminating external components, reducing board space, increasing flexibility and lowering manufacturing costs.

As the newest additions to the PurePath digital family of products, the TAS5152 and TAS5142 are pin-for-pin compatible and take advantage of integrated MOSFETs, improved gate drive technology and innovative overcurrent (OC) detection. Integrating two channels in a single package eases board layout, simplifies heat sink assembly and reduces the system bill of materials.

The TAS5142 and TAS5152 incorporate new intelligent gate drive technology that reduces sensitivity to routing modifications without affecting electromagnetic interference (EMI) performance. The power stages also support TI's latest innovation, a two-stage over-current detector, which manages over-currents, avoiding unnecessary shut downs and protecting against short circuit conditions. This feature allows the power stage to drive real world speakers with minimum audible artifacts during high power peaks in the audio source, while still protecting the power stage from high current conditions.

OC detection protects the power stage from high current levels caused by shorted speaker wires. However, peaks in the audio signal, and/or speakers with impedance droops, can trigger the sensing circuit, causing the speaker's audio output to be interrupted. TI's two-stage over-current detector improves the listener experience by virtually eliminating audio artifacts due to an interrupted audio stream. The TAS5152 and TAS5142 also allow the engineer to program the OC level to customize this setting according to the filtering inductors used.

The TAS5152 and TAS5142 digital amplifiers are based on TI's PurePath digital technology, which allows consumer electronics manufacturers to build completely digital, end-to-end audio products with cutting-edge sound reproduction and the most lifelike sound in a compact form factor.

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The TAS5152 and TAS5142 digital amplifier power stages, which are pin-for-pin compatible, are available now. Both are packaged in a 36-pin PSOP3 package and priced at $4.30 and $3.90 each, respectively, in 1,000-piece quantities. The TAS5142 will also be available in a 44-pin PowerPad package for applications that don't need to drive two channels at 100 W simultaneously with expected release in the second quarter.Click here for the TAS5142 data sheet.Click here for the TAS5152 data sheet.

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In the short time that these stereo digital amplifiers have been sampling, TI has begun shipping volume orders to four customers, which is indicative of this killer combo product — a single chip, digital input amplifier that's able to drive two channels with intelligent gate drive technology and OC detection, said Kevin Belnap, TI's marketing manager for digital home audio.

This is the first time a single-chip amplifier will be able to drive two channels of 100 W per channel, as well as 125 W per channel. The predecessor to TI's latest products, the TAS5121 device, drove one channel of 100 W at 4Ω.

Typically, these parts are used in home theatre systems — where you have six channels. Now, you can cut down on the number of power stage amplifiers that you use. If you are driving six channels in a DVD receiver, for instance, you can now use three components, instead of six.

Intelligent gate driver technology and two-stage OC detection are key features that make this product stand out.

Basically, TI is using intelligence to control the MOSFETs within the power stage. The MOSFETs are providing power to the speaker.

By the way, these are Class D amps, which isn't something TI generally promotes about its PurePath devices. “In the past, we haven't marketed them as such partly because of the negative perception of Class D amps,” Belnap said. However, Belnap believes that this perception is finally changing.

Most of the amps being used today in the world are Class AB. However, in the home theatre market, Class D amps are dominating, according to Belnap. Essentially, Class D amps provide a cost advantage over anything above 50 W per channel, Belnap said. Additionally, consumers want increased functionality, such as a DVD player, tuner, decoding capability and six-channel amplified output, all in a small box, which can't be accomplished with Class AB amps, he explained. “Class AB's low efficiency requires a very large heatsink to dissipate the wasted heat. To include all this functionality would make the chassis too large,” he added.

From a quality standpoint, however, Class AB amps have a leg up over Class D amps since they can deliver lower THD.

If you need to meet .001 percent THD for professional audio equipment, this isn't the technology for you since it's intended for consumer applications, Belnap said. TI's digital amplifiers are nothing to sneeze at though in terms of audio quality — with 110-dB SNR and less than 0.06 percent at 1 W (and less than 0.2 percent THD up to 80 W).

While TI admits that it's not the only player touting overcurrent detection (OC), the company does lay claim to handling more current than anyone else. TI's TAS5142/TAS5152 devices can handle up to 10 amps, versus only 3 amps from competing devices, Belnap said. “We can handle higher current in a way that's less audible to the user,” he explained.

For example, a certain note or frequency within a song may cause a high current spike through your speaker. Before TI's latest digital amplifier architecture, the power stage couldn't tell the difference between a speaker impedance drop and a true short circuit. Therefore, in previous generation amplifiers, the system would shut down to protect itself against the high current. To the listener — there was an audible “click,” which occurred on the order of 1 milliseconds. It was short — but you still heard the click. With today's amplifiers, however, since it's a two stage OC detection architecture, the first stage goes into current limited mode to recover from the overcurrent extremely fast (in the microsecond region), which is inaudible — well, maybe your dog could hear it!

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