Audio subsystem houses Class D speaker

Santa Clara, Calif. — National Semiconductor Corp.'s audio subsystem with a mono Class D speaker driver is said to integrate all the analog and digital functions needed for smart phones and voice-over-Internet Protocol (VoIP) phones.

National's LM4935 is a complete audio subsystem with multiple digital and analog inputs and outputs. Operating on supplies ranging from 1.8 volts to 5.5 V, the LM4935 combines several features: a Class D speaker amplifier delivering 570 milliwatts into an 8-ohm load; a stereo headphone amplifier that supports output capacitor-less (OCL) or AC-coupled operation delivering 30 mW per channel into a 32-ohm load; a mono earpiece amplifier delivering 30 mW into a 32-ohm load; and a line output for an external-powered hands free speaker providing filterless Class D stereo speaker capability. Other features include a successive approximation register (SAR) analog-to-digital (A/D) converter for system monitoring and a high-fidelity digital-to-analog (D/A) converter.

The LM4935's bidirectional I2S digital interface with pulse-code modulation (PCM) capability transmits any audio file or voice data transmission back and forth from the baseband application-specific integrated circuit (ASIC) or processor to the analog outputs. The subsystem also features a read/write I2C compatible digital interface.

The company's new 4 x 4-mm micro SMDxt package saves up to 70 percent board space over existing packages, said Mike Polacek, vice president of National's Audio Products Group. A member of the Boomer audio power amplifier family, the LM4935 audio subsystem provides high-quality output power with a minimal number of external components, he said.

In addition, the LM4935 gives engineers design flexibility in arranging analog inputs through a sophisticated switching/mixing circuitry, eliminating the need for external audio switches and mixing components, according to Polacek.

Two analog inputs allow the LM4935 to accept a stereo signal from an FM radio or operate as two separate mono inputs that can accept other analog input signals. Additional analog inputs allow for differential mono input and output from a GSM, CDMA or other cell phone radio module as well as a baseband ASIC.

See related block diagram

Available now in a 49-bump micro SMDxt package, the LM4935 is priced at $3.95 each in 1,000-unit quantities. Click here for the LM4935 data sheet.

National Semiconductor , 1-800-272-9959,

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