New Industry Products

National Adds Smallest Audio Subsystem

January 08, 2006 by Jeff Shepard

The LM4935 from National Semiconductor Corp. claims the title of the industry's smallest audio subsystem with a mono Class D speaker driver. The new device integrates the analog and digital audio functions needed for smart phones and voice-over-Internet protocol (VoIP) phones.

In a related announcement, National released additional details of the subsystem's new 4 mm by 4 mm micro SMDxt package, which saves up to 70 percent board space over existing packages.

"Smart phones bring the convergence of PDA functionality, wireless connectivity and, increasingly, consumer audio to one full-featured device," said Mike Polacek, vice president of National's Audio Products Group. "The LM4935 allows handset designers to add the new audio features consumers demand. Its integration drives design simplicity and takes up a minimum amount of board space."

The LM4935 includes multiple digital and analog inputs and outputs. Operating on supplies ranging from 1.8V to 5.5V, the LM4935 combines several features: a Class D speaker amplifier delivering 570 mW 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 handsfree speaker providing filter-less Class D stereo speaker capability. Other features include a successive approximation register (SAR) analog-to-digital converter (ADC) for system monitoring and a high-fidelity digital-to-analog converter.

The LM4935's bi-directional 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.

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. 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 application-specific integrated circuit (ASIC). Two additional inputs support internal and external microphone capability.

National's new micro SMDxt package provides high input/output analog devices with the smallest possible footprint for any given pin count. The micro SMDxt, which builds on the success of National's micro SMD package, utilizes a unique solder ball structure that enables high-reliability products with bump counts up to 100 bumps at a 0.5 mm pitch. With the new package, reliability requirements for typical portable applications such as thermal cycling, thermal shock, drop test and flex test can be met without the use of an underfill.

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