New Class-D Amplifier for Portable Consumer Electronics from Analog Devices

The SSM2301 and SSM2304 Class-D amplifiers employ sigma-delta modulation to reduce EMI and filterless topology to conserve board space

Analog Devices introduce two Class-D audio amplifiers designed to meet the low-power, small size, and growing sound quality requirements of portable electronics. A leader in delivering innovative sound processing solutions for home and professional applications, ADI is applying its expertise to Class-D amplifiers that address the space constraints and battery-consumption requirements of cellular handsets, handheld game machines, MP3 players, laptop computers, and handheld media devices.

ADI&tsquo;s SSM2301 and SSM2304 Class D amplifiers are designed to efficiently drive speakers in handheld and portable consumer applications by consuming minimal power, employing sigma-delta modulation to reduce electromagnetic interference (EMI) emissions, and integrating a filterless topology that eliminates external components.

“Combining the power-saving and space-saving benefits of Class-D audio technology with ADI's linear IC expertise has enabled a portfolio of audio amplifiers that deliver exceptional sound for a range of applications from portable devices such as cellular handsets and MP3 players, to thin flat panel advanced televisions and multi-channel surround-sound car stereos,” said Steve Sockolov, product line director, Precision Signal Processing.

“While most Class-D amplifiers use some variation of pulse-width modulation (PWM), ADI's Class-D amplifiers use a sigma-delta pulse density modulation (PDM) to reduce the amplitude of spectral components at high-frequencies, thus significantly minimizing EMI emissions.”

High Efficiency and Low-Power Consumption for Portable Electronics
The SSM2301 (mono) and SSM2304 (stereo) devices operate at a very high 85 percent efficiency over a wide range of output power levels. The SSM2301 delivers 1.4 W into an 8 ohm load, and the SSM2304 delivers 2 W of power into a 4 ohm load. Both devices operate on a single 2.5 V to 5.5 V supply, have a micro-shutdown mode with a maximum shutdown current of 20 nA, and feature a built-in thermal shutdown and output short circuit protection. The ability to function at very low voltages makes them ideal for applications, such as cellular handsets, where the speaker amplifiers are driven directly from the battery voltage.

Small Packaging and Exceptional Audio Fidelity
The new Class-D audio amplifiers are housed in tiny 8-lead, 3 mm x 3 mm lead-frame chip-scale packaging (LFCSP). Board space is further conserved with a filterless topology that eliminates external output filters.

The SSM2301 and SSM2304 have less than 1 percent total harmonic distortion plus noise (THD+N) when driving peak output loads from a 5 V supply, and a signal-to-noise ratio (SNR) that is better than 98 dB. The fully-differential input provides excellent rejection of common-mode noise on the input. The amplifiers also include click-and-pop suppression circuitry that reduces audible noise on activation and deactivation and feature flexible fixed and user-adjustable gain configurations.

The SSM2301 and SSM2304 are the most recent additions to ADI's portfolio of Class-D amplifiers, which also includes the AD199x family of audio power amplifiers.

The Analog Devices website address is www.analog.com
[Reprinted with kind permission from Analog Devices]