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National speaker drivers promote credit-card thin handset designs

Posted: 11 Jan 2005 ?? ?Print Version ?Bookmark and Share

Keywords:national semiconductor? boomer? audio amplifier?

National Semiconductor Corp. unveiled a new trio of Boomer audio amplifiers that it says will result in "credit-card-thin" handsets and reduced power consumption.

The new LM4960, LM4961 and LM4802B are the industry's first integrated single-chip devices to drive ceramic and piezoelectric speakers in portable applications, according to the company. 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 one gram and consume less than 5mW of power.

Japan's Panasonic Mobile Communications, the first company in the industry to design a ceramic speaker into a cellphone, selected National's LM4802B and LM4961 speaker drivers for their new line of phones. In addition to cellphone applications, the LM4802B, LM4960 and LM4961 devices can also be designed into space-constrained portable applications such as PDAs, smartphones, notebook computers and other small handheld devices.

The new single-chip devices integrate a boost converter with an audio power amplifier, replacing the need for expensive voltage regulators and other external components and freeing up space in designs. The LM4802B and LM4961 audio speaker drivers deliver 12Vp/p for ceramic speaker applications and the LM4960 delivers 24Vp/p for piezoelectric speakers.

These amplifiers feature a low-power consumption shutdown mode and an internal thermal shutdown protection mechanism. In addition, they contain advanced "pop and click" circuitry to eliminate noises that typically occur during turn-on and turn-off transitions. All three speaker drivers allow the flexibility of running a handset at a low voltage, increasing talk time in cellular applications. National's new amplifiers provide additional benefits such as reduced component count and electromagnetic interference and noise, as well as increased space savings and performance for customers.

The LM4960 is designed for piezoelectric speakers. It integrates a switching regulator, a current-mode boost converter operating at a fixed frequency of 1.6MHz, to drive a dual audio power amplifier. It delivers 24Vp/p mono-bridge-tied load (BTL) to a piezoelectric speaker with less than 1 percent total harmonic distortion plus noise (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.

Available in 28-pin pullback LLP packages, the LM4802B is priced at $1.65 and the LM4961 at $2.10. The LM4960 is housed in a 28-pin non-pullback LLP package and is available for $2.50. All pricing is in 1,000-unit quantities. Additional information can be found at National's website.

- Bettyann Liotta

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