Switched-Capacitor Voltage Inverter with Shutdown# ADM8828ART Technical Documentation
## 1. Application Scenarios
### Typical Use Cases
The ADM8828ART is a switched capacitor voltage inverter primarily employed in portable electronic systems requiring negative voltage rails from positive supplies. Key applications include:
- LCD Bias Generation : Generating negative bias voltages (-5V to -15V) for LCD displays in handheld devices
- Op-Amp Power Supplies : Providing dual supply voltages (±2.5V to ±5V) for operational amplifiers in single-supply systems
- Data Acquisition Systems : Creating negative reference voltages for ADCs and signal conditioning circuits
- Portable Instruments : Powering analog circuits in battery-operated measurement equipment
### Industry Applications
- Consumer Electronics : Smartphones, tablets, digital cameras for display and audio circuitry
- Medical Devices : Portable monitoring equipment requiring dual power supplies
- Industrial Controls : Sensor interfaces and measurement systems
- Communications Equipment : RF circuits and interface electronics
### Practical Advantages
Strengths:
- High Efficiency (85% typical) : Superior to resistive dividers for voltage inversion
- Compact Solution : Requires only 4 external capacitors (no inductors)
- Low Quiescent Current (150µA typical) : Ideal for battery-powered applications
- Wide Input Range (1.5V to 5.5V) : Compatible with various battery technologies
- Small Package (SOT-23-6) : Minimal board space requirements
Limitations:
- Limited Output Current (25mA maximum) : Not suitable for high-power applications
- Output Voltage Drop : Approximately 50mV at 10mA load
- Switching Noise : Requires careful filtering in noise-sensitive applications
- Temperature Dependency : Performance varies across operating temperature range
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Insufficient Decoupling
- Problem : Output ripple exceeding specifications
- Solution : Use low-ESR ceramic capacitors (1µF recommended) at both input and output
Pitfall 2: Layout-Induced Noise
- Problem : Switching noise coupling into sensitive analog circuits
- Solution : Implement proper grounding and keep switching nodes away from analog traces
Pitfall 3: Overcurrent Conditions
- Problem : Device shutdown or damage under excessive load
- Solution : Ensure load current remains below 25mA maximum rating
### Compatibility Issues
Positive Aspects:
- Direct Interface : Compatible with most CMOS/TTL logic levels
- Battery Systems : Works well with Li-ion, NiMH, and alkaline batteries
- Microcontrollers : Easily controlled by GPIO pins of common MCUs
Potential Conflicts:
- Noise-Sensitive Circuits : May interfere with high-precision analog systems
- Low-Voltage Systems : Minimum 1.5V input requirement limits ultra-low-voltage applications
- High-Frequency Systems : Switching frequency (50kHz typical) may create beat frequencies
### PCB Layout Recommendations
Critical Layout Guidelines:
1. Component Placement :
- Place charge pump capacitors (C1, C2) within 5mm of IC pins
- Position input/output capacitors adjacent to respective pins
2. Routing Priorities :
- Keep switching node traces (C1+, C1-, C2+, C2-) short and direct
- Use ground plane for improved noise immunity
- Route sensitive analog signals away from charge pump circuitry
3. Thermal Management :
- Provide adequate copper area for heat dissipation
- Avoid placing heat-sensitive components nearby
4. Power Distribution :
- Use separate traces for analog and digital ground returns
- Implement star-point grounding for mixed-signal systems
## 3.
