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Ultrasmall audio amps claim highest RF immunity

Posted: 03 Sep 2009 ?? ?Print Version ?Bookmark and Share

Keywords:audio amplifier? RF immunity? Class D amplifier?

ISL99202 audio amp

Intersil Corp. has introduced two new audio amplifiers that claim to feature the industry's lowest power consumption, smallest size and highest RF immunity.

The ISL99201 and ISL99202 are the first audio products in a new family of ultrasmall-footprint packages that will enable smaller, thinner and lighter consumer devices that run longer on a battery charge. These audio amps are suited for use in smart phones, PDAs, game consoles, MP3 and personal media players, PNDs and LCD TVs.

The ISL99201, available in 9-bump 0.4mm pitch WCSP, is said to be the smallest Class D amplifier. It is a filterless, fully-integrated, high-efficiency mono amplifier capable of delivering up to 2.5W into a 4? load. It features a low-noise modulation scheme, operating with 86 percent efficiency at 400mW into 8?, and has a SNR that is better than 95dB. The ISL99201 also includes a micropower shutdown mode with a typical shutdown current of 200nA. The fully-differential input of the ISL99201 provides 75dB rejection to common mode noise on the input. The ISL99201 is available in three fixed-gain settings that reduce BOM costs and save board space. It is also available with programmable gain setting option for design flexibility. In addition to the WCSP package, the ISL99201 is available in an 8-lead TDFN package.

Available in 12-bump 0.4mm pitch WCSP, Intersil's ISL99202 is claimed to be the smallest stereo capfree headphone amplifier and supports 16? to 600? speaker impedance. Its ultrawide operating voltage of 2.4V to 5.5V makes the new amplifier suitable for use in mobile battery-powered applications that use 2 AA or single cell Li-ion batteries, as well as in notebook computers using 3.3V to 5V power supplies. It is also available in 12-lead TQFN package.

Implementing immunity
With the proliferation of wireless technology, audio amplifiers are routinely exposed to RF energy. For example, even though phones using the GSM protocol operate at frequencies between 800MHz and 1,900MHz, the data transfers in bursts at 217Hz, which is in the audio frequency range. Many competitive amplifiers reproduce this noise in the headphones which results in the now familiar "bumble bee" buzz. Some audio amplifiers detect the 217Hz signal, akin to demodulation of FM transmissions, and amplify it to the headphone output. The ISL99202 has a unique input architecture which suppresses this demodulation and prevents the bursts at 217Hz from interfering with the audio output.

In addition, the bursts at 217Hz cause spikes on the power supply. Some poorly designed amplifiers couple these power supply spikes through the amplifier outputs, resulting in an audible buzz. Amplifiers typically have a parameter called PSRR, which specifies the ability of the amplifier to reject noise from the power supply. The ISL99202 is designed to have the highest PSRR in its class, which also contributes to its industry-leading RF immunity.

The ISL99202 also features audiophile quality SNR and THD specifications, and Intersil's click-and-pop suppression technology. Comprehensive protection features include undervoltage and short-circuit protection, as well as thermal shutdown.

The ISL99201 is available now in 8-lead TDFN packages with prices starting at $0.56 each in 1,000-unit quantities. In 9-bump WCSP, prices start at $0.47. The ISL99202 is sampling now in 12-lead TQFN and 0.4mm pitch 12-ball WLCSP, with 1,000-unit pricing of $0.72 and $0.65, respectively.

For application notes on audio amplifiers click here.

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