Maxim introduces the MAX97200 dual-mode Class H headphone amplifier designed for battery-powered portable devices. The amplifier uses Maxim's proprietary DirectDrive II technology to build an extremely efficient Class H architecture. The MAX97200 is nearly twice as efficient as a Class AB amplifier, extending audio playback time. In addition, the device's interference-free switching architecture and flawless/humming performance provide end users with a richer audio experience. The IC is only 2mm2 in size and is the smallest stereo headphone amplifier on the market. The MAX97200 is ideal for cellular phones, portable media players (PMPs), notebooks, and other battery-powered audio applications.
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The challenge: improving amplifier efficiency
Today's portable consumer electronics support a variety of multimedia features, but it also affects battery life. This problem is becoming more prominent in every new design today, as designers are constantly integrating camera modules, HD video, web browsing and many other features into next-generation devices as needed. In order to maintain this "functional expansion" capability, system designers must find new ways to extend battery life.
Choosing the right amplifier is critical to saving power. For example, Class AB amplifiers are known for their low efficiency and are powered by the largest supply voltage regardless of the level of the audio signal. This approach results in an efficiency of only 13% to 15% at normal listening levels (providing 2mW to 5mW power to a 16Ω load).
In contrast, Class H amplifiers (referred to as Class G in Europe) are capable of switching between multiple internally generated sources based on the magnitude of the output signal. By quickly selecting the supply voltage, Class H amplifiers can increase the efficiency of the output stage while minimizing the dynamic distortion of the output stage. Compared to Class AB amplifiers, the MAX97200 is 97% more efficient. The MAX97200 achieves efficiencies ranging from 20% to 29% over the 2mW to 5mW output power range.
DirectDrive II technology builds the lowest power H-class architecture
Maxim's DirectDrive II technology uses an internal dual-mode charge pump to generate ±PVIN and ±PVIN/2 supplies from an external 1.8V regulated source. The MAX97200 operates from a ±PVIN/2 supply with a low output signal amplitude and switches to a ±1.8V supply only when the load requires a large output. Due to the low amplitude of most audio signals, the power consumption of the MAX97200 is comparable to that of a traditional ±0.9V DirectDrive amplifier. To further save power, the device consumes less than 1μA in shutdown mode and only 1.15mA (typ) in normal operation.
Interference-free audio performance
One of the challenges of the Class H architecture is that it is necessary to switch the power supply before the output signal changes to a larger value, otherwise the audio output will have a significant clipping effect and produce dynamic distortion. Maxim's Class H technology has a unique tracking function that predicts the level change of the audio signal for seamless power regulation. This approach ensures signal continuity without the interference signals common to competing amplifiers.
The MAX97200 delivers industry-leading click-and-pop performance when entering and exiting shutdown mode due to the device's extremely low output offset voltage. Because the DirectDrive II architecture produces a ground-referenced output from a single supply, eliminating the large DC-blocking capacitors typically required between the amplifier output and the headphone load. This feature ensures that no annoying hum and hum is produced, providing a better listening experience for end users.
In addition, the MAX97200 has a high signal-to-noise ratio (SNR = 105dB) to ensure high-fidelity sound in the system. The output noise of the device is only 5.6μV, which improves the overall audio noise floor and does not produce a click when there is no signal.
Optimized for small package sizes
The MAX97200 is the smallest and most efficient headphone amplifier on the market, available in a tiny (1.27mm x 1.65mm), 12-bump wafer-level package (WLP), which is 25% smaller than the nearest competitor. Because the MAX97200 does not require an inductor, its overall solution size is 30% lower than competing devices.
The MAX97200 operates from a single 1.8V supply and delivers 34mW of output power for a 32Ω load. The device operates over the -40°C to +85°C extended temperature range.
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