High-Efficiency, Adaptive Charge Pump 5V Boost # Technical Documentation: FAN5665UCX LED Driver
Manufacturer : FAIRCHILD (now part of ON Semiconductor)
Component Type : Switched-Capacitor Voltage Doubler / White LED Driver
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## 1. Application Scenarios
### Typical Use Cases
The FAN5665UCX is a charge-pump based DC/DC converter specifically designed for driving series-connected white LEDs. Its primary function is to provide a regulated current source for LED backlighting applications.
Primary Applications:
- Mobile Device Backlighting : Powers 2-4 series-connected white LEDs in mobile phones, PDAs, and portable media players
- LCD Display Illumination : Provides constant current for monochrome or color LCD displays requiring uniform backlighting
- Keypad Lighting : Illuminates keypads and function buttons in handheld devices
- Indicator Lighting : Drives high-brightness white LEDs for status indicators and decorative lighting
### Industry Applications
- Consumer Electronics : Smartphones, feature phones, digital cameras, portable gaming devices
- Industrial Handhelds : Barcode scanners, portable measurement devices, handheld terminals
- Medical Devices : Portable medical equipment displays, diagnostic tool illumination
- Automotive : Interior lighting, dashboard illumination (secondary applications with proper environmental qualification)
### Practical Advantages
- High Efficiency : Typical efficiency of 85-90% across operating range
- Compact Solution : Requires minimal external components (only 3 capacitors)
- Precision Current Regulation : ±5% typical LED current accuracy
- Low Noise Operation : Constant frequency switching reduces audible noise
- Dimming Capability : Supports PWM dimming for brightness control
- Low Quiescent Current : <1μA in shutdown mode extends battery life
- Integrated Soft-Start : Limits inrush current during startup
### Limitations
- Limited Output Current : Maximum 30mA per LED channel (4 channels total)
- Fixed Topology : 1x/1.5x/2x charge pump modes only - not suitable for wide input voltage ranges
- Thermal Constraints : No integrated thermal protection - requires external thermal management at high ambient temperatures
- LED Configuration : Only supports series-connected LEDs, not parallel configurations
- Frequency Fixed : 1MHz fixed switching frequency may cause EMI issues in sensitive applications
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Inadequate Input/Output Capacitors
- Problem : Excessive output ripple or instability
- Solution : Use low-ESR ceramic capacitors (X5R or X7R dielectric) with values ≥2.2μF for input and ≥1μF for output
Pitfall 2: Improper LED Current Setting
- Problem : LED brightness variation or premature failure
- Solution : Calculate RSET resistor precisely using formula: RSET(Ω) = 17500 / ILED(mA)
Pitfall 3: Thermal Management Issues
- Problem : Component overheating in high ambient temperatures
- Solution : Ensure adequate PCB copper area for heat dissipation, avoid placing near other heat sources
Pitfall 4: EMI/RFI Interference
- Problem : Noise coupling into sensitive analog circuits
- Solution : Implement proper grounding, use shielded inductors if necessary, add ferrite beads on input lines
### Compatibility Issues
Compatible Components:
- Microcontrollers : Compatible with standard GPIO interfaces for enable and PWM dimming control
- Power Sources : Works with Li-ion batteries (2.7V-5.5V), regulated DC supplies
- LEDs : Compatible with most white LEDs with forward voltage 3.0V-3.6V
Potential Incompatibilities:
- High
