CMOS Switched-Capacitor Voltage Converters# ADM660AN Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The ADM660AN is a switched-capacitor voltage converter IC primarily used for voltage inversion and voltage doubling applications. Common implementations include:
- Negative Voltage Generation : Converting +5V to -5V for operational amplifier power supplies
- Voltage Doubling : Generating +10V from +5V input for higher voltage requirements
- Battery-Powered Systems : Creating dual supply rails from single battery sources
- Signal Conditioning Circuits : Providing negative bias voltages for analog circuits
### Industry Applications
Industrial Automation :
- PLC analog I/O modules requiring ±12V supplies
- Sensor signal conditioning circuits
- 4-20mA current loop transmitters
Telecommunications :
- RS-232 interface level shifting
- Line driver/receiver power supplies
- Modem analog front ends
Medical Equipment :
- Portable medical monitoring devices
- Biomedical sensor interfaces
- Patient isolation circuitry
Consumer Electronics :
- Audio amplifier bias supplies
- LCD display contrast controls
- Portable instrumentation
### Practical Advantages and Limitations
Advantages :
- High Efficiency : Typically 95-98% conversion efficiency
- Minimal External Components : Requires only 4 external capacitors
- Wide Operating Range : 1.5V to 6.0V input voltage
- Low Quiescent Current : 120μA typical (ADM660AN)
- Compact Solution : SOIC-8 package saves board space
Limitations :
- Limited Output Current : Maximum 50mA output current
- Switching Noise : Generates high-frequency noise (20kHz typical)
- Voltage Drop : Output voltage decreases with increasing load current
- Temperature Sensitivity : Performance degrades at temperature extremes
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Insufficient Output Current Capability
- Problem : Attempting to draw >50mA causes voltage collapse
- Solution : Use external buffer amplifier for higher current requirements
Pitfall 2: Excessive Output Ripple
- Problem : High ripple voltage affecting sensitive analog circuits
- Solution : Implement LC filtering with 10μH inductor and 10μF capacitor
Pitfall 3: Startup Issues
- Problem : Failure to start under heavy capacitive loads
- Solution : Add soft-start circuit or limit output capacitance to <100μF
### Compatibility Issues
Digital Circuit Interference :
- The 20kHz switching frequency can interfere with sensitive analog measurements
- Mitigation : Physical separation from analog sections and proper grounding
Mixed-Signal Systems :
- Switching noise may couple into high-impedance analog nodes
- Solution : Use separate ground planes and star grounding techniques
Microcontroller Integration :
- Ensure power sequencing compatibility with microcontroller reset circuits
- Add power-on reset delay if necessary
### PCB Layout Recommendations
Power Supply Routing :
- Use wide traces (≥20 mil) for all power connections
- Place input and output capacitors as close as possible to IC pins
- Implement separate ground pours for analog and digital sections
Component Placement :
```
Recommended Layout:
+-----------------+
| C1 ADM660AN C3 |
| (SOIC-8) |
| C2 C4 |
+-----------------+
```
- C1, C2: Flying capacitors (0.22μF ceramic)
- C3: Input bypass capacitor (10μF tantalum)
- C4: Output filter capacitor (10μF tantalum)
Thermal Management :
- Provide adequate copper area for heat dissipation
- Maximum junction temperature: 125°C
- Derate output current at
