CMOS Switched-Capacitor Voltage Converter# ADM660 Technical Documentation
## 1. Application Scenarios (45% of content)
### Typical Use Cases
The ADM660 is a switched-capacitor voltage converter IC primarily used for voltage inversion and voltage doubling applications. Key use cases include:
- Negative Voltage Generation : Converting +5V to -5V for operational amplifier power supplies
- Battery-Powered Systems : Creating dual supply rails from single battery sources
- Signal Conditioning Circuits : Providing negative bias voltages for analog front-ends
- LCD Display Drivers : Generating contrast adjustment voltages
- Data Acquisition Systems : Powering analog sections requiring symmetrical supplies
### Industry Applications
Industrial Automation :
- PLC analog I/O modules requiring ±12V from single 24V supplies
- Sensor signal conditioning circuits
- Process control instrumentation
Consumer Electronics :
- Portable audio equipment (headphone amplifiers)
- Digital cameras (LCD bias generation)
- Mobile devices requiring multiple voltage rails
Medical Devices :
- Portable monitoring equipment
- Diagnostic instrument front-ends
- Patient monitoring systems
Telecommunications :
- Line interface circuits
- Modem power supplies
- Network interface cards
### Practical Advantages and Limitations
Advantages :
- High Efficiency : Typically 85-95% conversion efficiency
- Compact Solution : Requires only external capacitors, no inductors
- Low Quiescent Current : ~120μA typical, ideal for battery operation
- Wide Input Range : 1.5V to 6.0V operation
- Simple Implementation : Minimal external component count
Limitations :
- Limited Output Current : Maximum 50mA output current
- Switching Noise : Generates high-frequency noise requiring careful filtering
- Voltage Drop : Output voltage decreases with increasing load current
- Temperature Sensitivity : Performance varies with operating temperature range
## 2. Design Considerations (35% of content)
### Common Design Pitfalls and Solutions
Pitfall 1: Insufficient Output Current Capability
- Problem : Attempting to draw >50mA causes voltage collapse
- Solution : Use parallel devices or external buffer for higher current requirements
Pitfall 2: Excessive Output Ripple
- Problem : High switching noise affects sensitive analog circuits
- Solution : Implement LC filtering and proper decoupling capacitors
Pitfall 3: Thermal Overstress
- Problem : Operating at maximum current without heat dissipation
- Solution : Include thermal vias and consider derating for high-temperature environments
Pitfall 4: Startup Issues
- Problem : Inrush current causing supply voltage sag
- Solution : Use soft-start circuits or current-limiting resistors
### Compatibility Issues with Other Components
Analog Circuits :
- Op-amps : Ensure adequate power supply rejection ratio (PSRR) at switching frequency
- ADCs : May require additional filtering to prevent switching noise coupling
- Sensors : Sensitive to power supply noise - implement proper isolation
Digital Circuits :
- Microcontrollers : Separate analog and digital grounds
- Communication Interfaces : I²C/SPI devices may require clean supplies
Power Management :
- LDO Regulators : Can help filter output but reduce overall efficiency
- DC-DC Converters : Avoid frequency interference by selecting different switching frequencies
### PCB Layout Recommendations
Power Stage Layout :
- Place flying capacitors (C1, C2) as close as possible to IC pins
- Use short, wide traces for high-current paths
- Implement ground plane for noise reduction
Decoupling Strategy :
- 10μF tantalum capacitor at input within 10mm of V+
- 10μF tantalum capacitor at output within 10mm of Vout
- 100nF ceramic
