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Amplifiers/Converters  

Class-D amplifier guarantees 90% efficiency

Posted: 14 May 2007  Print Version  Bookmark and Share

Keywords:Class D amplifier  stereo power amps  soft switch technology 

Rohm Co. Ltd has developed the BD5421EFS Class D stereo amplifier LSI for audio-equipped sets with strict thermal design and dimensional requirements, such as LCD and plasma TVs, minicomponent stereos, power speakers and gaming devices.

The efficiency of conventional analog amplifiers is often poor, approximately 50 percent, with half of the power being converted to heat. This requires large heat sink or cooling fans, making it difficult to reduce set thickness.

Rohm's class D stereo amplifier LSI utilizes cutting-edge BiCDMOS processes for minimal line resistance and output transistor ON-resistance, resulting in an industry-leading 90 percent efficiency (10W+10W output at 8Ω load), low heat generation. The 34W (17W+17W) output is enabled using a small back-surface metal plate with excellent thermal dissipation characteristics, eliminating the need for a heat sink. As a result, sets can be made smaller and thinner and power consumption reduced dramatically.

Additional features include low input conversion noise (5.6µVrms)—well below that of conventional class D power amplifiers—for clear audio, as well as proprietary soft switching technology for a smooth signal waveform envelope when turning the mute on and off. And PWM modulation sampling clock master/slave functionality eliminates beat noise generated due to clock differences during synchronous multiple amplifier operation, such as in 5.1-channel systems.

The device can drive standard loads up to 4Ω. It reduces popping noises during power interruption when turning on and off. The soft-switch technology of the amps provides high-quality sound muting. Beat noise resulting from differences in sampling clock frequency is eliminated using a synchronous master/slave function when multiple amplifiers are used simultaneously.

The power amps have a gain adjustable via external resistance (20-37dB). It has an internal PWM sampling clock frequency that can be adjusted (200-400kHz), reducing unwanted radiation in the AM radio band. It also enables configuration of a high-power 34W mono amplifier by connecting stereo outputs in parallel.

The device's HTSSOP-A44 package incorporates a small back-surface metal package enabling 34W (17W + 17W) output without the need for a heat sink. Sample price starts at $4.2.




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