Class D makes audio chip Grade A
By Richard A Quinnell, Contributing Editor -- EDN, January 5, 2006
Available in a 4×4-mm package, the LM4935 audio chip provides a complete subsystem for smart phones and VOIP (voice-over-Internet Protocol) handsets. The device handles many common analog and digital input and output formats and includes a Class D speaker amplifier that delivers 570 mW into an 8Ω load.
Flexibility is the LM4935’s hallmark. It can accept digital-audio data in PCM (pulse-code-modulation) format over a bidirectional I2S or I2C digital link. For analog input signals, built-in switching and mixing circuitry allow the device to accept a stereo signal, two separate mono signals, differential mono signals from a cell-phone radio module, and internal or external microphones. The output lines support OCL (output-capacitorless) or ac-coupled drives of 30 mW into a 32Ω load, an earpiece amplifier, and a line output for an external amplifier. Other features include a SAR (successive-approximation-register) ADC for system monitoring and a high-fidelity DAC.
The device comes in a 49-bump micro-SMD package with 0.5-mm pitch and costs $3.95 (1000). National also offers online design tools at http://webench.national.com and seminars at its main Web site.
National Semiconductor, www.national.com.
