LM4850 Audio Amplifier - Summary

1. Overview:

️· The LM4850 is a power amplifier designed for audio applications.
️· It supports both bridged-tied load (BTL) and single-ended (SE) modes.

2. Key Features & Functionality:

️· Shutdown Function: Reduces power consumption when inactive. A logic high (>= 2.0V) to the SHUTDOWN pin disables the amplifier.
️· Headphone Control (HP-IN): Switches between BTL and SE modes. A logic low activates BTL, a logic high activates SE. Connected via a voltage divider with the headphone plug.
️· Unity-Gain Stability: Allows designers to optimize system performance.
️· Bypass Capacitor Importance: Critical for low noise and high power supply rejection. Close to device.
️· Input Impedance: 20kΩ
️· Bandwidth: 100Hz - 20kHz ± 0.25dB
️· Power Output: Designed for 1W @ 8Ω

3. Design Considerations & Recommendations:

️· Power Supply: Minimum 4.7V. A 5V supply is common.
️· Gain: Keep gain as low as practical for best signal-to-noise and minimal distortion.
️· External Components:
- Input and Output Capacitors: Size based on desired low-frequency response, balancing performance with cost/space constraints.
- Resistors: Recommended values for the differential gain calculation for desired gain and impedance.
️· Power Dissipation: Stay within limits to prevent overheating.

4. Design Example (1W / 8Ω Bridged Amplifier):

️· Parameters:
- Power Output: 1W RMS
- Load Impedance: 8Ω
- Input Level: 1V RMS
- Bandwidth: 100Hz - 20kHz ± 0.25dB
️· Calculations:
- Minimum Supply Voltage: ~4.7V (but 5V is typical)
- Differential Gain: Set to a value of 3.
- Resistor Values: Calculated to achieve desired gain and impedance (R1 = 20k, Rf = 30k)

5. Important Notes:

️· Proper supply bypassing is essential.
️· Refer to the datasheet "Typical Performance Characteristics" graphs for power vs. supply voltage, dropout voltage, and power dissipation information.