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National Semiconductor Corporation (NS) has announced a single-chip Boomer® audio power amplifier with the industry's highest output voltage featuring ceramic speakers that can be driven in 3V powered portable devices. Since the chip can drive ceramic speakers with a higher supply voltage, the sound pressure level (SPL) of the sound system can be increased, and the output volume can be further increased according to the needs of the application. The LM48555 chip drives ceramic speakers for portable electronics, making it ideal for small, slim handheld electronic products such as mobile phones, smart phones, and notebook computers.

The LM48555 can support 1uF+20 Ohm ceramic speaker loads with peak/peak drive voltages up to 15.7V and total harmonic distortion and noise (THD+N) below 1%. In addition, the chip is available in a tiny 12-bump micro SMD package measuring just 1.5mm x 2.0mm, allowing manufacturers to take advantage of this small and slim form factor to develop a variety of versatile ultra-thin phones.

Ceramic speakers require a high-voltage, low-current operating environment that is quite different from traditional moving-coil speakers. The main advantage of ceramic speakers is that they are lightweight and slim. Voice coil speakers are typically as thick as 4mm or more, while ceramic speakers are only 0.7mm thick and weigh less than 1g.

The LM48555 can use a 3V DC power supply to output a peak/peak voltage of 15.7V. If the supply voltage is 5V, the quiescent current can be as low as 7.5mA (typical). Since the LM48555 has a low-power shutdown mode, it can save more power. In addition, the chip uses a differential input transmission method, so its noise suppression capability is higher. Taking 217 Hz noise as an example, the power supply rejection ratio (PSRR) can reach 80 dB (typical). Another advantage of using the LM48555 chip is that no startup capacitor or transient voltage suppression circuitry is required. In addition, this amplifier incorporates an advanced switching/switching noise suppression circuit that eliminates the noise generated during on/off. The built-in boost regulator of the LM48555 has a soft-start function that minimizes transient currents during power-up.

The LM48555 is available in a 12-bump, thin micro SMD package and is priced at $1.95 each in 1,000-unit quantities.

September 22, 2018