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audio/videoZONE Products for the week of April 13, 2009
Texas Instruments Says…
TPA6140A2: Extend Music Playback Time With Lowest Power Class-G Headphone Amplifiers
Amplifiers improve system-level music playback time by 20% over Class-AB technology
Users of music phones and MP3 players can benefit from dramatically extended music playback time enabled by two new 25-mW Class-G, DirectPath stereo headphone amplifiers from Texas Instruments Incorporated (TI), which adjust their voltage supplies to the audio signal to minimize power dissipation. In a standalone Lithium-Ion battery test between TI's Class-G technology and a competing ground-referenced Class-AB device, the TPA6140A2 and TPA6141A2 reduced power consumption by 30 percent. The amplifiers improve system-level music playback time by 20 percent over Class-AB technology in the best-in-class music phones shipping today.
"Consumers traveling from Dallas to Delhi or from San Francisco to Shanghai want to listen to their MP3s for the duration of the flight without worrying whether they have enough battery life left to make a call when they land,” said Art George, senior vice president of TI's High-Performance Analog business unit. "Devices like the TPA6140A2 and TPA6141A2 save critical battery life to make this scenario a reality.”
Other key features significantly improve sound quality. The amplifiers feature TI's field-proven DirectPath technology, which eliminates the need for large DC-blocking capacitors at the amplifier outputs to give designers additional board space and allow consumers to enjoy greater low-frequency audio fidelity. In addition, the TPA6140A2 and TPA6141A2 include built-in pop suppression circuitry, which completely eliminates disturbing pop noise when the amplifier powers on, to enable a seamless audio experience. Power supply rejection of greater than 100 dB and differential inputs improve noise rejection, while 100-dB signal-to-noise ratio (SNR) improves the signal quality to deliver crystal clear audio.
EN-Genius Says…
The Class-G audio amplifiers I have seen up to now have not truly been the kind of devices that I would have expected. With only two rails available those devices are more like power-switched Class-AB parts. One part I have seen – which has not yet been released uses three rails, a little better.
TI has gone for the full Class-G McCoy with variable rails. With an on-board switch-regulator the supply voltages (with the negative rail provided by a charge pump) varies with the audio input levels. With a supply voltage rate change faster than audio frequencies the audio never hits a clipping or distortion level. The buck converter switching frequency is a nominal 600 kHz and the charge pump is well outside the audio band at above 300 kHz (depending on output power level).
The audio inputs are detected for level. The highest of the stereo channels triggers an optimizer and comparator (compared with the operational voltage level). The loop is completed with filtering and chopping with a ramp generator to drive the gates of on-chip power MOSFETs powered by the exernal supply. An external switch inductor and capacitor are required. The provided supply rail can be between 2.5 V and 5.5 V.
TI includes its usual click-and-pop suppression together with short-circuit and thermal protection. The charge pump, supplying the negative rail, ensures that the stereo audio outputs swing around ground and eliminates any output coupling capacitor. Two external capacitors are required for the charge pump. There is an I2C interface which is compatible with the earlier – and higher power – TPA6130A2 register map. The gain range over I2C control is from -59 dB to +4 dB with 1% gain matching between channels.
The inputs can be configured either differentially or single-ended with a single-ended input resistance of 15.6 kΩ at +4 dB gain (double the resistance for differential). The 1% THD at 2.7 V supply and 1 kHz is 25 mW into 16 Ω. The 10% THD mark is reached very quickly at 32 mW. At a fairly useful power level of 20 mW into 32 Ω the THD+N is 0.01%. PSRR is a typical 105 dB while CMRR is 68 dB. SNR is a typical 105 dB at +4 dB gain. Interchannel crosstalk is -80 dB.
This is another winner from TI. Getting a Class-G amplifier with a variable supply rail, instead of just switching between supplies is a breakthrough for the company and the technology. My small quibble would be that the useful (non-distorted) power levels may be marginal for some portable applications. The pricing indicates TI expects very high volume sales – and I wouldn’t disagree with them. There will be a switched gain version coming soon, the TPA6141A2, which can be set to either 0 dB or +6 dB gain. It is likely to be more popular, particularly if TI shaves another ten cents from the pricing.
The TPA6140A2 is in production in WCSP-16 priced at $0.95 in 1000-piece lots.
Data Sheet
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