LM380N - Power Audio Amplifier

Overview

The LM380N is a power audio amplifier designed for consumer applications, offering a cost-effective solution with fixed internal gain and ground-referenced inputs. Its self-centering output and wide supply voltage range make it suitable for various audio amplification needs. The device is engineered to deliver reliable performance while minimizing system costs, making it ideal for mass-produced audio products.

Features

• Fixed Internal Gain: 34 dB (50x voltage gain) eliminates the need for external gain-setting components.
• Wide Supply Voltage Range: Operates from 10V to 22V, accommodating various power supply configurations.
• Ground-Referenced Inputs: Unique input stage allows inputs to be referenced to ground, simplifying circuit design.
• Self-Centering Output: Automatically biases the output to half the supply voltage, reducing DC offset issues.
• High Peak Current Capability: Supports up to 1.3A output current for driving low-impedance loads.
• Low Distortion: Designed for minimal harmonic distortion in audio applications.
• Thermal Protection: Built-in thermal shutdown prevents damage from overheating.
• Short-Circuit Protection: Robust design protects against output short circuits.

Applications

The LM380N is widely used in consumer audio applications where cost-effectiveness and reliability are critical. Typical use cases include:

• Intercom systems
• Television audio amplifiers
• Portable audio devices
• Alarm systems
• AM/FM radio amplifiers
• Low-power PA (Public Address) systems
• Game consoles
• Toys with audio output

Electrical Characteristics

The following specifications are typical at 25°C with Vcc = 18V unless otherwise noted:

DC Characteristics

• Supply Voltage Range: 10V to 22V
• Quiescent Current: 7 mA (typical)
• Output Voltage Swing: 12V peak-to-peak (min) with RL = 8Ω, Vcc = 18V
• Input Bias Current: 100 nA (typical)
• Input Resistance: 150 kΩ (typical)

AC Characteristics

• Voltage Gain: 34 dB (fixed)
• Bandwidth: 100 kHz (typical)
• Total Harmonic Distortion: 0.2% (typical) at 1W, 1kHz
• Power Output: 2.5W (typical) into 8Ω at 18V
• Slew Rate: 0.3 V/μs (typical)

Protection Features

• Thermal Shutdown: Activates at approximately 150°C
• Short-Circuit Current: Limited to 1.3A (typical)

Package Information

The LM380N is available in a standard 14-pin dual in-line package (DIP) with the following mechanical specifications:

14-Pin DIP Package Dimensions

• Package Type: PDIP-14
• Length: 19.3 mm (max)
• Width: 6.35 mm (max)
• Height: 4.57 mm (max)
• Lead Pitch: 2.54 mm
• Lead Width: 0.51 mm (min)
• Lead Length: 3.3 mm (min)
• Operating Temperature Range: 0°C to +70°C
• Storage Temperature Range: -65°C to +150°C

Pin Configuration

The pinout for the 14-pin DIP package is as follows:

• Pin 1: Gain (Bypass)
• Pin 2: Non-Inverting Input
• Pin 3: Inverting Input
• Pin 4: Ground
• Pin 5: Ground
• Pin 6: Ground
• Pin 7: Output
• Pin 8: Vcc (Supply Voltage)
• Pin 9: Compensation
• Pins 10-14: No Connection

Design Considerations

When implementing the LM380N in a circuit design, several factors should be considered to ensure optimal performance:

Power Supply Decoupling

Proper power supply decoupling is essential for stable operation. A 100μF electrolytic capacitor should be placed close to the Vcc pin (Pin 8) to ground, with a 0.1μF ceramic capacitor in parallel for high-frequency noise suppression.

Heat Dissipation

While the LM380N is relatively robust, proper heat sinking may be required for continuous operation at higher power levels. The package can dissipate approximately 1W without a heat sink in free air at 25°C ambient temperature.

Input Configuration

The input stage is designed for ground-referenced operation. For single-ended input, the non-inverting input (Pin 2) should be used with the inverting input (Pin 3) grounded through a small resistor (typically 10Ω) to maintain stability.

Output Load Considerations

The amplifier is designed to drive loads as low as 4Ω, though 8Ω is more typical for most applications. When driving reactive loads (such as speakers), a Zobel network (series RC) may be required across the output to prevent high-frequency oscillations.

Typical Application Circuit

A basic application circuit for the LM380N includes:

• Input coupling capacitor (typically 1μF)
• Power supply decoupling capacitors (100μF electrolytic and 0.1μF ceramic)
• Optional output Zobel network (0.1μF capacitor in series with 10Ω resistor)
• Bypass capacitor (10μF) from Pin 1 to ground for noise reduction

Conclusion

The LM380N provides a simple, cost-effective solution for low to medium power audio amplification needs. Its fixed gain architecture eliminates the need for external components typically required for gain setting, while its robust protection features ensure reliable operation in consumer applications. The wide supply voltage range and self-centering output make it particularly versatile for various audio system designs.