Innovative Audio Amplification with LM4906
The widely recognized LM386 stands as a popular choice for compact audio power amplifiers, offering a single-chip solution for 1-watt audio needs. However, the LM386 demands several external components, including electrolytic capacitors, increasing both circuit size and cost. National Semiconductor has recently introduced its Boomer® audio integrated circuits, focusing on delivering high-quality audio with minimal external components (available in surface mount packaging only). Among these, the LM4906 shines, capable of delivering 1 watt of continuous average power to an 8-ohm load with less than 1% distortion (THD+N) from a +5 V power supply. Remarkably, the LM4906 efficiently operates with a minimal external PSRR (Power Supply Rejection Ratio) bypass capacitor of just 1 μF. What sets it apart is the absence of output coupling capacitors or bootstrap capacitors, making it an ideal choice for low voltage portable applications, especially in cellphones.
Enhanced Safety with Internal Thermal Shutdown
The LM4906 goes the extra mile in ensuring safety by incorporating an internal thermal shutdown mechanism. This built-in feature acts as a safeguard, preventing overheating and potential damage. Additionally, the LM4906 offers flexibility in amplification with its internal selectable gain, allowing users to choose between 6 dB or 12 dB amplification levels based on their specific requirements.
Advantages of Bridge Amplifier Design
Choosing a bridge amplifier design like the LM4906 offers distinct advantages over single-ended configurations. One significant benefit lies in its ability to provide differential drive to the load, effectively doubling the output swing for a given supply voltage. This translates to four times the output power compared to a single-ended amplifier operating under similar conditions, especially in scenarios with low supply voltages (ranging from 5 to 6 volts). However, it’s essential to address potential heating issues due to increased power demands. To counter this, additional copper foil can be strategically added, reducing thermal resistance and enabling higher power output without triggering the thermal shutdown protection circuitry.
Efficiency and Space Optimization in Portable Designs
In portable applications, space and cost considerations are paramount. The LM4906’s bridge configuration eliminates the need for an output coupling capacitor, a requirement in single-ended amplifier setups. This is especially advantageous in portable designs, where large input capacitors can be expensive and take up significant space. By accurately sizing the input capacitor based on necessary low-frequency response, the system’s performance can be optimized without unnecessary expenses or wasted space. Furthermore, this approach minimizes turn-on pops, enhancing the overall user experience.