MAX98425A: 22V Stereo Class‑D Amplifier with High Efficiency & Ultra‑Low IQ
The MAX98425A is a high-efficiency, stereo Class-D speaker amplifier with industry-leading quiescent power featuring Envelope Tracking control, Brownout Prevention Engine (BPE), Dynamic Headroom Tracking (DHT), and RMS Limiter.
The MAX98425A supports sample rates up to 192kHz and a higher passband (for fS > 50kHz) to enable high-resolution audio and ultrasound use cases. A separate bypass path is available for inputs, such as an ultrasound signal, so that it is not attenuated by audio processing. SSM and edge-rate control minimize EMI and eliminate the need for output filtering found in traditional Class-D devices.
The Envelope Tracking algorithm on the device monitors the incoming audio signal and generates a PWM signal to control an external DC-DC converter to keep the amplifier supply close to the peak output audio signal, thereby improving system efficiency, idle quiescent power consumption, and thermal efficiency.
For battery-powered applications, the BPE helps avoid a system brownout by reducing the device’s current consumption. This is achieved by either attenuating or limiting the amplifier output when the device supply drops below a set of programmable thresholds. In addition, as the amplifier supply varies due to sudden transients and declining battery life, DHT automatically optimizes the headroom available to the amplifier to maintain a consistent distortion level.
The device provides a PCM interface for audio data and a standard I2C interface for control data communication.
Thermal foldback, when enabled, automatically reduces the output power when the temperature exceeds a user-specified threshold. This allows for uninterrupted music playback even at high ambient temperatures. Traditional thermal protection is also available in addition to robust overcurrent protection.
Key Features and Benefits
- Wide Input Supply Range (3V to 22V)
- Ultra-Low Quiescent Power
- 89mW at VPVDD = 14V, MAX98425A
- Ultra-Low 28.5μVRMS Output Noise
- Low Distortion
- -81.1dB THD+N at 2W into 8Ω, f = 1kHz
- MAX98425A Output Power at 1% THD+N:
- 28W Stereo into 8Ω, VPVDD = 22V
- 20.5W into 4Ω, VPVDD = 14V
- MAX98425A Speaker Amplifier Efficiency:
- 87.5% at 1W per ch. into 8Ω, VPVDD = 22V
- 88% at 1W per ch. into 4Ω, VPVDD = 14V
- Class-D EMI Reduction Enables Filterless Operation
- SSM and Switching Edge Rate Control
- Integrated Speaker Current and Voltage Feedback, Do Not Require External Components (MAX98415A only)
- Flexible Brownout Prevention Engine
- I2S/16-Channel TDM and I2C Digital Interfaces
- Playback and IV Paths Support Sample Rates up to 192kHz
- No MCLK Required
- Dynamic Headroom Tracking (DHT)
- Envelope Tracking Output to Maximize System Efficiency
- Extensive Click-and-Pop Suppression
- 40-Bump WLP (0.4mm Pitch)
Applications
- Soundbars
- Mobile Speakers and Smart Speakers
- Tablets, Laptops, and Desktop Computers
- Smart IoT Devices
Evaluation Board
The MAX98425A can be evaluated with the MAX98425AEVSYS
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