Smartphone Amp Delivers Enriched Sound, Power Savings in Tiny Package

Smartphones are increasingly expected to provide not only basic audio, but also high-quality stereo with additional features to maximize the performance of the small speakers as well as improve gaming and video streaming. The Cirrus Logic CS35L41 smart power amplifier targets this growing trend with enriched audio clarity and loudness plus advanced power management (Fig. 1).

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1. The Cirrus Logic CS35L41 smart power amplifier includes high-performance, DSP-enhanced audio, a Class H voltage boost, and a Class D audio amplifier.

This “boosted” Class D audio amplifier with digital signal processing (DSP), and supported by the company’s SoundClear Playback software, provides improved audio quality, increases the apparent loudness of smartphone speaker output, and protects the speaker using a pairing of hardware and software. The CS35L41 comes in a small package claimed to be nearly half the size of other leading DSP smart amps.

Although it’s a mono device, even a stereo pair requires very little PCB real estate, due to its 5.64 mm², 30-ball, wafer-level chip-scale package (WLCSP), which is claimed to be 74% smaller than nearest smart-amplifier competitor (Fig. 2).

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2. A pair of CS35L41 devices, needed for stereo, requires little overall real estate due to its 5.64-mm²WLCS package.

The vendor maintains that this digital input, >5-W output, Class D amplifier has the lowest noise and idle power consumption in its class. Basic audio-output specifications include 11-V boosted output of 5.3 W at 1% THD + noise, reaching 6.0 W at 10% THD + noise. An integrated Class H dc-dc converter boosts the supply voltage and adaptively tracks the audio level, yielding improved efficiency compared to Class G topologies (Fig. 3).

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3. The graph of Class G and Class H supply rail voltage versus time shows the added efficiency that the former approach provides for audio signals with wide dynamic range.

Power consumption is, of course, a major consideration in portable devices, so the CS35L41 integrates an advanced battery-management system along with predictive algorithms. These adapt to changing audio, speaker, and battery conditions to minimize consumption and battery current, but without diminishing audio performance (Fig. 4).

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4. The predictive battery-management algorithm further enhances the power-efficient performance.

The CS35L41 operates from a single 2.5- to 5.5-V rail; idle-channel noise is 9 µV while idle-state power is 6.8 mW. Supported interfaces include industry-standard I²S, TDM, and PDM formats. This Cirrus Logic smart power amplifier is currently shipping in production volumes.