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issue: September 2008 APPLIANCE Magazine

Electronics Report
Amplified Savings

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Cost savings and reliability are key features behind new amplifiers for HDTVs and other home audio products.

New amplifiers with single-ended outputs are designed to eliminate components, offering engineers cost savings and slim form factors when designing LCD, plasma, and DLP TVs.

As industrial design and increasingly smaller form factors become standard in the HDTV market, manufacturers face increasing price and size pressures. Texas Instruments (TI; www.ti.com) of Dallas, TX, U.S., says its new TPA3121D2 and TPA3124D2 amplifier solutions address these challenges.

The 15-W, stereo analog-input Class-D amplifiers use single-ended architectures to reduce bill of material (BOM) costs and save board area by eliminating two LC output filters. To further reduce cost, both devices can run off the existing 24-V backlight rail in an LCD HDTV, eliminating the need for a dedicated power rail. With greater than 90% efficient operation, there is no need for a heat sink. As a result, TI says, audio solutions based on the new devices can offer OEMs up to 25% lower
BOM cost compared with competitive products.

Ryan Kehr, new product definition manager for TV audio products, says the amplifiers have been carefully designed to overcome the “click and pop” challenges typically associated with single-ended designs. “It proves difficult to minimize voltage glitches at the output during power supply transitions, including power-on, power-off, and mute,” Kehr says.

“There are several methods to ramp the sound in an amplifier,” he continues. “Ramping it in a linear fashion would cause a significant pop. TI ramps the TPA3121D2 and TPA3124D2 in an S-curve fashion. This slow, controlled method is achieved by transitioning the output from a very fine duty cycle up to 50 percent, which reduces pop.”

Along with single-ended stereo support, the amplifiers’ outputs can be configured in BTL mode to support 30-W mono applications, such as wireless speakers or subwoofers. In addition, the TPA3124D2 features a fast mute time of 30 microseconds. Depending on the video processor, Kehr says a faster mute may be necessary to reduce power-loss pop. “The mute acts as a gatekeeper, enabling designers to mute the amplifier before there is power loss upstream, which results in pop,” Kehr explains.

To ensure reliability, both devices are fully protected with integrated self-protection circuits against faults, including overvoltage, undervoltage, overtemperature, and short circuit. For instance, thermal protection on the TPA3121D2 prevents damage to the devices when the internal die temperature exceeds 150°C. “Once the die temperature exceeds the thermal set point, the device enters into the shutdown state, and the outputs are disabled,” Kehr explains. “This is not a latched fault. The thermal fault is cleared once the temperature of the die is reduced by 30°C. The device begins normal operation at this point with no external system interaction.”

Short-circuit protection circuitry on the outputs prevents damage to the device during output-to-output shorts and output-to-ground shorts after the filter and output capacitor at the speaker terminal. “When a short circuit is detected on the outputs, the part immediately disables the output drive,” Kehr says. “This is an unlatched fault. Normal operation is restored when the fault is removed.” 

Suppliers mentioned in this article:
Texas Instruments

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