31 May 2007

National Semiconductor Delivers Industry’s
Most Powerful Ceramic Speaker Driver

National Semiconductor Corporation today introduced a single-chip Boomer® audio power amplifier that delivers the industry’s highest voltage for driving ceramic speakers used in a wide range of 3V portable devices. Driving the ceramic speaker at higher voltages allows it to produce a higher sound-pressure level (SPL) for applications that require louder sound. The LM48555 drives ceramic speakers in cell phones, smartphones, notebook computers and other small handheld devices.

With a ceramic speaker load equivalent to 1 uF + 20-Ohms, the LM48555 provides a voltage drive of 15.7V peak-to-peak with less than 1 percent total harmonic distortion plus noise (THD+N). In addition, the LM48555’s tiny 12-bump micro SMD package has a footprint of 1.5 mm by 2.0 mm, making it possible for manufacturers to create ultra-thin, feature-rich handsets.

Ceramic speakers require higher voltage, but less current compared to traditional moving coil speakers. The primary benefits of ceramic speakers are their thin profile and light weight. Voice coil speakers are typically 4 mm or more in thickness, while ceramic speakers are only 0.7 mm thick and often weigh less than one gram. More information on these speaker types is available in National’s Audio Education Series eBooks at audio.national.com.

Key Features – LM48555 Boomer Audio Power Amplifier

The LM48555 delivers 15.7V peak-to-peak from a 3V DC power supply, and typically offers low quiescent current of 7.5 mA from a 5V supply. The LM48555 can achieve additional battery savings with its low power shutdown mode, and its differential inputs improve noise rejection. Power supply rejection ratio (PSRR) is typically 80 dB at 217 Hz. The LM48555 does not require bootstrap capacitors or snubber circuits.

The amplifier’s advanced “pop-and-click” circuitry eliminates noise that typically occurs during turn-on and turn-off transitions. The LM48555’s integrated boost regulator features a soft start function that minimizes transient current during power-up.