DALLAS ( ChipWire) -- Texas Instruments Inc. is set to introduce a Class D audio amplifier this week that will increase the efficiency and lower the cost of audio systems in laptop computers and USB speakers, the company said. The TPA2000D2 is expected to subtract $1.25 to $1.75 from the bill of materials of such systems, said Ted Thomas, product marketing manager for audio amps at TI.
The TPA2000D2 is considered a "third-generation" stereo amplifier, capable of delivering 2 watts into 3-ohm speakers. Total harmonic distortion plus noise is less than 0.07 percent at 1 W (at 1 kHz with a 4-ohm load). TI said the main advantage of the TPA2000D2 is the reduction in output filter components it enables. A preliminary data sheet for the part stated the output filters could consist of "three small capacitors and two small inductors per channel. "This looks like a Class AB board in terms of simplicity," Thomas said.
Class D amplifiers, which are based on pulse-width modulators, offer higher efficiency than the traditional Class AB topologies. High-frequency square waves of constant amplitude, but varying width, are output from the switching regulator. The width and frequency of the pulses are proportional to the amplitude of the audio signal. The PWM signals are applied to power DMOS H-bridges, which provide high output current to drive the speaker coils.
Previous Class D devices, such as TI's own TPA005D14, needed a sometimes-complex inductor and capacitor network as an output filter to strip off the switching artifacts from the PWM. That adds up to $2 to the bill of materials, Thomas said. In the TPA2000D2, an elevated switching frequency of 250 kHz reduces the filter requirements.
The TPA2000D2 uses a three-state PWM that shifts the phase relationships between positive- and negative-going pulses on its output, so that the pulses are effectively out of phase at the zero crossing. According to TI, this appears to double the output frequency of the switcher, but effectively eliminates much of the dc component of the output signal and reduces the inductive filter requirement.
The devices will be manufactured in an LBC-3S fabrication process -- a linear CMOS used for op amps and power supply controllers, Thomas said.