Low Voltage Dual 35mW Audio Power Amplifier Circuits (BTL 300mW)# AN7118 Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The AN7118 is a monolithic integrated circuit designed primarily as a low-voltage audio power amplifier for portable electronic devices. Its typical applications include:
- Portable Audio Players : Provides 1-2W output power for personal listening devices
- Battery-Powered Radios : Operates efficiently at voltages as low as 3V
- Intercom Systems : Suitable for voice communication applications
- Toy Electronics : Cost-effective amplification for simple audio applications
- Educational Kits : Simple implementation for electronics learning projects
### Industry Applications
Consumer Electronics
- Portable cassette players and CD players
- Handheld gaming devices with audio output
- Small tabletop radios and clock radios
Communication Devices
- Cordless telephone base stations
- Simple intercom and paging systems
- Two-way radio accessories
Automotive Accessories
- Aftermarket car audio amplifiers (low-power applications)
- Automotive alarm system sounders
### Practical Advantages and Limitations
Advantages:
- Low Power Consumption : Typical quiescent current of 15mA enables extended battery life
- Minimal External Components : Requires only 5 external components for basic operation
- Wide Operating Voltage : 3.5V to 12V operation accommodates various power sources
- Thermal Protection : Built-in thermal shutdown prevents damage from overheating
- Compact Package : Available in 9-pin SIP package for space-constrained designs
Limitations:
- Limited Output Power : Maximum 2.2W output restricts use to small speakers
- Frequency Response : 40Hz-20kHz range may not suit high-fidelity applications
- Heat Dissipation : Requires proper heatsinking at higher power levels
- Modern Alternatives : Newer Class-D amplifiers offer better efficiency
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Power Supply Issues
- Pitfall : Inadequate power supply decoupling causing oscillation
- Solution : Place 100μF electrolytic and 0.1μF ceramic capacitors close to VCC pin
Thermal Management
- Pitfall : Overheating when driving 4Ω loads at maximum voltage
- Solution : Implement proper heatsinking and limit continuous output power
Input Signal Handling
- Pitfall : Input overdrive causing distortion
- Solution : Include input attenuator for signals exceeding 200mV RMS
### Compatibility Issues with Other Components
Microcontroller Interfaces
- The AN7118 requires DC blocking capacitors when interfacing with microcontroller PWM audio outputs
- Input impedance of 100kΩ may require buffer stages for high-impedance sources
Speaker Compatibility
- Optimal performance with 8Ω speakers
- 4Ω speakers possible but require derated operation to prevent thermal shutdown
Power Supply Requirements
- Compatible with standard linear regulators (78xx series)
- Switching regulators may require additional filtering to suppress noise
### PCB Layout Recommendations
Power Supply Routing
- Use star grounding technique with separate analog and power ground paths
- Route power traces with minimum 1mm width for current handling
Component Placement
- Position decoupling capacitors within 10mm of IC power pins
- Keep input components away from output stage to prevent feedback
Thermal Management
- Provide adequate copper pour for heatsinking (minimum 500mm²)
- Consider thermal vias if using multilayer boards
- Ensure free airflow around the package in enclosed designs
## 3. Technical Specifications
### Key Parameter Explanations
Electrical Characteristics (Typical @ Vcc=6V, RL=8Ω, Ta=25°C unless specified)
| Parameter | Value | Conditions |
|-----------|-------|------------|
| Operating Voltage | 3.5-
