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SSM2375 Filterless High Efficiency Mono 3 W Class-D Audio Amplifier

The SSM2375 is a fully integrated, high efficiency, 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 3 W of continuous output power with <1% THD + N driving a 3 Ω load from a 5.0 V supply.

The SSM2375 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. The SSM2375 operates with 93% efficiency at 1.4 W into 8 Ω or with 85% efficiency at 3 W into 3 Ω from a 5.0 V supply and has an SNR of >100 dB.

Spread-spectrum pulse density modulation (PDM) is used to provide lower EMI-radiated emissions compared with other Class-D architectures. The inherent randomized nature of spread-spectrum PDM eliminates the clock intermodulation (beating effect) of several amplifiers in close proximity.

The SSM2375 includes an optional modulation select pin (ultralow EMI emissions mode) that significantly reduces the radiated emissions at the Class-D outputs, particularly above 100 MHz. In ultralow EMI emissions mode, the SSM2375 can pass FCC Class B radiated emission testing with 50 cm, unshielded speaker cable without any external filtering.

The device also includes a highly flexible gain select pin that allows the user to select a gain of 0 dB, 3 dB, 6 dB, 9 dB, or 12 dB. The gain selection feature improves gain matching between multiple SSM2375 devices within a single application as compared to using external resistors to set the gain.

The SSM2375 has a micropower shutdown mode with a typical shutdown current of 20 nA. Shutdown is enabled by applying a logic low to the SD pin.

The device also includes pop-and-click suppression circuitry. This suppression circuitry minimizes voltage glitches at the output during turn-on and turn-off, reducing audible noise on activation and deactivation.

Other features that simplify system-level integration of the SSM2375 include input low-pass filtering to suppress out-of-band DAC noise interference to the PDM modulator and fixed-input impedance to simplify component selection across multiple platform production builds.

The SSM2375 is specified over the industrial temperature range of −40°C to +85°C. It has built-in thermal shutdown and output short-circuit protection. It is available in a halide-free, 9-ball, 1.5 mm × 1.5 mm wafer level chip scale package (WLCSP).

Applications

• Mobile phones
• MP3 players
• Portable electronics

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