Single-Chip Power Amp Drives Ceramic Speakers

The LM48555 single-chip Boomer audio power amplifier from National Semiconductor drives ceramic speakers in a range of 3-V dc portable devices. By driving these speakers at higher voltages, the amp produces a higher sound-pressure level (SPL) for applications that require louder sound. With a ceramic speaker load equivalent to 1 µF + 20 Ω, the LM48555 provides a voltage drive of 15.7 V p-p with less than 1% total harmonic distortion plus noise (THD+N).

Also, the amp provides a quiescent current of 7.5 mA from a 5-V supply. Its low-power shutdown mode also saves power, while its differential inputs improve noise rejection. Its power-supply rejection ratio (PSRR) is typically 80 dB at 217 Hz. The LM48555 doesn't require bootstrap capacitors or snubber circuits. Its advanced "pop and click" circuitry eliminates noise that usually occurs during turn-on and turn-off transitions. And, it's available in a 12-bump thin micro SMD package that measures 1.5 by 2.0 mm.