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SSM2537 PDM Digital Input, Mono 2.5 W Class D Audio Amplifier

The SSM2537 is a PDM digital input Class D power amplifier that offers higher performance than existing DAC plus Class D solutions. The SSM2537 is ideal for power sensitive applications where system noise can corrupt the small analog signal sent to the amplifier, such as mobile phones and portable media players.

The SSM2537 combines an audio digital-to-analog converter (DAC), a power amplifier, and a PDM digital interface on a single chip. The integrated DAC plus analog Σ-Δ modulator architecture enables extremely low real-world power consumption from digital audio sources with excellent audio performance. Using the SSM2537, audio can be transmitted digitally to the audio amplifier, significantly reducing the effect of noise sources such as GSM interference or other digital signals on the transmitted audio. The SSM2537 is capable of delivering 2.5 W of continuous output power with <1% THD + N driving a 4 Ω load from a 5.0 V supply.

The SSM2537 features a high efficiency, low noise modulation scheme that requires no external LC output filters. The closed-loop, three-level modulator design retains the benefits of an all-digital amplifier, yet enables very good PSRR and audio performance. The modulation continues to provide high efficiency even at low output power and has an SNR of 103 dB PDM input. Spread-spectrum pulse density modulation is used to provide lower EMI-radiated emissions compared with other Class D architectures.

The SSM2537 has a four-state gain and sample frequency selection pin that can select two different gain settings, optimized for 3.6 V and 5 V operation. This same pin also controls the internal digital filtering and clocking, which can be set for 64 × fS or 128 × fS input sample rates to support both 3 MHz and 6 MHz PDM clock rates.

The SSM2537 has a micropower shutdown mode with a typical shutdown current of 1 µA for both power supplies. Shutdown is enabled automatically by gating input clock and data signals. A standby mode can be entered by applying a designated PDM stop condition sequence. The device also includes pop-and-click suppression circuitry. This suppression circuitry minimizes voltage glitches at the output when entering or leaving the low power state, reducing audible noises on activation and deactivation.

The SSM2537 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 9-ball, 1.3 mm × 1.3 mm wafer level chip scale package (WLCSP).

Applications

• Mobile handsets

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