LM4871M - Bridge-Connected Audio Power Amplifier

Overview

The LM4871M is a high-performance, bridge-connected audio power amplifier designed to deliver high-quality audio output with minimal external components. This IC is capable of providing 1.1W of continuous average power to an 8Ω load with low distortion (0.5% THD) when operating from a 5V power supply. The device is optimized for portable audio applications where space and power efficiency are critical considerations.

With its integrated thermal shutdown protection and externally controlled low-power consumption shutdown mode, the LM4871M offers both reliability and power management capabilities. The amplifier's bridge-tied load (BTL) configuration eliminates the need for output coupling capacitors, making it ideal for space-constrained designs.

Features

• Bridge-tied load (BTL) configuration eliminates output coupling capacitors
• 1.1W continuous average output power into 8Ω at 5V supply (0.5% THD)
• Low quiescent current: 4mA typical
• External shutdown control for power management
• Internal thermal shutdown protection
• Improved power supply rejection ratio (PSRR): 60dB at 217Hz
• Unity-gain stable
• No output "pop" during power-up or shutdown
• Surface-mount SOIC package for compact designs
• Wide supply voltage range: 2.7V to 5.5V

Applications

The LM4871M is particularly suited for portable and space-constrained audio applications, including:

• Mobile phones and smartphones
• Portable media players
• Tablet computers
• Notebook and laptop computers
• Personal digital assistants (PDAs)
• Portable gaming devices
• USB-powered speakers
• Battery-powered audio devices
• Multimedia docking stations

Electrical Characteristics

All specifications are given for VDD = 5V, TA = 25°C, RL = 8Ω unless otherwise noted.

Absolute Maximum Ratings

• Supply Voltage (VDD): 6V
• Input Voltage (VIN): -0.3V to VDD + 0.3V
• Storage Temperature Range: -65°C to +150°C
• Junction Temperature: 150°C
• Lead Temperature (soldering, 10 sec): 260°C

Operating Characteristics

• Supply Voltage Range: 2.7V to 5.5V
• Quiescent Current: 4mA typical (VDD = 5V, no load)
• Shutdown Current: 0.1μA typical (SHUTDOWN = GND)
• Output Power: 1.1W typical (8Ω, 5V, 0.5% THD)
• Total Harmonic Distortion + Noise (THD+N): 0.5% typical (1W, 8Ω, 5V)
• Power Supply Rejection Ratio (PSRR): 60dB typical (217Hz)
• Input Resistance: 60kΩ typical
• Shutdown Turn-On Time: 10ms typical
• Shutdown Turn-Off Time: 1ms typical

Package Information

The LM4871M is available in an 8-pin SOIC (Small Outline Integrated Circuit) package with the following dimensions:

• Package Type: SOIC-8
• Package Code: M
• Body Width: 3.9mm
• Body Length: 4.9mm
• Height: 1.75mm max
• Lead Pitch: 1.27mm
• Operating Temperature Range: -40°C to +85°C

Pin Configuration

• Pin 1: SHUTDOWN - Active high shutdown control input
• Pin 2: VIN - Audio signal input
• Pin 3: GND - Ground reference
• Pin 4: GND - Ground reference
• Pin 5: VOUT- - Negative amplifier output
• Pin 6: VDD - Positive power supply
• Pin 7: VOUT+ - Positive amplifier output
• Pin 8: BYPASS - Bypass capacitor connection

Design Considerations

Power Supply Decoupling

Proper power supply decoupling is critical for optimal performance. A 0.1μF ceramic capacitor should be placed as close as possible to the VDD pin (Pin 6) and ground. For best performance in noisy environments, an additional 4.7μF to 10μF electrolytic capacitor may be used in parallel.

Thermal Management

While the LM4871M includes internal thermal shutdown protection, proper PCB layout can help maximize performance. Ensure adequate copper area is available for heat dissipation, especially when operating at maximum output power for extended periods.

Input Configuration

The amplifier is unity-gain stable and requires minimal external components. A DC blocking capacitor may be needed if the input signal has a DC component. The input impedance is typically 60kΩ, which should be considered when designing the input network.

Performance Characteristics

The LM4871M delivers excellent audio performance across its operating range:

• Frequency Response: 20Hz to 20kHz (±0.5dB typical)
• Signal-to-Noise Ratio: >90dB (A-weighted)
• Output Voltage Swing: 3.6Vpp typical (VDD = 5V, RL = 8Ω)
• Channel Separation: >60dB (1kHz)

Conclusion

The LM4871M bridge-connected audio power amplifier offers an excellent combination of performance, efficiency, and compact size for portable audio applications. With its 1.1W output capability, low power consumption, and integrated protection features, it provides a robust solution for designers needing high-quality audio amplification in space-constrained applications. The device's simple external component requirements and surface-mount package make it particularly suitable for modern portable electronics where board space is at a premium.