Rohm Semiconductor has developed USB-host audio-decoder ICs compatible with MP3 compression. The BU9457KV is MP3-only, while the BU9458KV is compatible with the MP3, WMA and AAC audio compression formats. The compact, monolithic USB-host audio ICs are intended for USB and SD memory audio players, which are supplanting CDs as the preferred choice to store and play back audio files. They are claimed to be the first decoder ICs that integrate protection circuits designed to prevent malfunction due to noise from the effects of wiring and nearby devices. Previously, external countermeasures—such as terminal-protection ICs and surge-protection diodes and resistors—have been necessary, especially in applications exposed to harsh operating environments, for example car audio. Both ICs integrate an improved communication error-recovery circuit in the USB interface block and provide ESD resistance to meet the requirements of the Electrostatic Discharge Immunity Test IEC 61000-4-2 Level 4 standard. According to the company, their level of ESD resistance makes them suitable for car-audio applications, which require excellent surge characteristics, although they can also be used as home and portable audio sets. Incorporating interface hardware such as USB host and SD memory controllers, along with a DAC, a sampling-rate converter, a compressed-audio-file decoder, a file system, and a system controller in a 12-12mm VQFP64 package makes it possible to play back music from USB memory and SD memory cards using a single chip. It allows simple command control without the need for a microcontroller, enabling configuration of a USB-host audio system by simply adding the chip to existing sets. The ICs can also be used in devices that did not previously support audio output, such as massage chairs and alarm clocks.
