NATIONAL Semiconductor, represented in Australia by Arrow Electronics , has released three Boomer audio amplifiers, single-chip devices that drive ceramic and piezoelectric speakers in portable applications.
The chips allow manufacturers to create credit-card-thin handsets or add additional features to designs. They save space and reduce power consumption, enabling longer battery life and talk time.
Ceramic and piezoelectric speakers are dramatically different from conventional moving coil speakers. They act as a capacitive rather than a resistive load and require much more voltage than current. In comparison to the 4mm or greater thickness of traditional moving coil speakers, ceramic speakers are only 0.7mm thick. They often weigh less than 1g and consume less than 5mW of power.
The LM4802B, LM4960 and LM4961 speaker drivers can also be used in space-constrained personal digital assistants (PDAs), smartphones, notebook computers and other small handheld devices.
They integrate a boost converter with an audio power amplifier, replacing the need for expensive voltage regulators and other external components and freeing up space. The LM4802B and LM4961 audio speaker drivers deliver 12V p/p for ceramic speaker applications and the LM4960 delivers 24V p/p for piezoelectric speakers.
These amplifiers feature a low-power consumption shutdown mode and an internal thermal shutdown protection mechanism. Pop and click circuitry eliminates noises that typically occur during turn-on and turn-off transitions. All three speaker drivers allow running a handset at a low voltage, increasing talk time in cellular applications. The amplifiers provide reduced component count, electromagnetic interference and noise.
The LM4960 is designed for piezoelectric speakers. It integrates a switching regulator and a current-mode boost converter operating at a fixed frequency of 1.6MHz to drive a dual-audio power amplifier. It delivers 24V p-p mono-BTL to a piezoelectric speaker with less than 1% THD+N while operating on a 3V power supply.
The LM4961 for ceramic speakers includes added battery savings, with a low-power mode for earpieces and a high-power mode to drive the ringtones and hands-free speakers.