2 × 2W Filterless Class-D Stereo Audio Amplifier

The SSM2356 is a fully integrated, high efficiency, stereo Class-D audio amplifier. It is designed to maximize performance for mobile phone applications. The application circuit requires a minimum of external components and operates from a single 2.5 V to 5.5 V supply. It is capable of delivering 2 × 2W of contin-uous output power with <1% THD + N driving a 4 Ω load from a 5.0 V supply.

The SSM2356 features a high efficiency, low noise modulation scheme that requires no external LC output filters. The modulation continues to provide high efficiency even at low output power. It operates with 92% efficiency at 1.4 W into 8 Ω or 85% efficiency at 2.0 W into 4 Ω from a 5.0 V supply and has an SNR of >103 dB.

Spread-spectrum pulse density modulation is used to provide lower EMI-radiated emissions compared with other Class-D architectures. The SSM2356 includes an optional modulation select pin (ultralow EMI emission mode) that significantly reduces the radiated emissions at the Class-D outputs, particularly above 100 MHz.

The SSM2356 has a micropower shutdown mode with a typical shutdown current of 20 nA. Shutdown is enabled by applying a logic low to the SDNR and SDNL pins. The device also includes pop-and-click suppression circuitry that minimizes voltage glitches at the output during turn-on and turn-off, reducing audible noise on activation and deactivation.

The fully differential input of the SSM2356 provides excellent rejection of common-mode noise on the input. Input coupling capacitors can be omitted if the dc input common-mode voltage is approximately VDD/2. The preset gain of SSM2356 can be selected between 6 dB and 18 dB with no external components and no change to the input impedance. Gain can be further reduced to a user-defined setting by inserting series external resistors at the inputs.

The SSM2356 is specified over the commercial temperature range (−40°C to +85°C). It has built-in thermal shutdown and output short-circuit protection. It is available in a 16-ball, 1.66 mm × 1.66 mm wafer level chip scale package (WLCSP).

Applications

* Mobile phones

* MP3 players

* Portable gaming

* Portable electronics

* Filterless stereo Class-D amplifier with Σ-Δ modulation

* No sync necessary when using multiple Class-D amplifiers from Analog Devices, Inc.

* 2 × 2W into 4 Ω load and 2x1.4 W into 8 Ω load at 5.0 V supply with <1% total harmonic distortion (THD + N)

* 92% efficiency at 5.0 V, 1.4 W into 8 Ω speaker

* >103 dB signal-to-noise ratio (SNR)

* Single-supply operation from 2.5 V to 5.5 V

* 20 nA shutdown current; left/right channel control

* Short-circuit and thermal protection

* Available in a 16-ball, 1.66 mm × 1.66 mm WLCSP

* Pop-and-click suppression

* Built-in resistors that reduce board component count

* User-selectable 6 dB or 18 dB gain setting

* User-selectable ultralow EMI emission mode