Serial LED Driver with Current-Regulated, Step-Up DC/DC Converter# Technical Documentation: FAN5606DMPX
Manufacturer : FAIRCHILD (now part of ON Semiconductor)
Component Type : White LED Driver / Charge Pump
Document Revision : 1.0
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## 1. Application Scenarios
### 1.1 Typical Use Cases
The FAN5606DMPX is a fractional charge pump IC designed primarily for driving white LEDs in portable electronic devices. Its core function is to provide a regulated current source for LED backlighting and indicator applications.
Primary Applications:
- Backlighting for LCD Displays : Powers 2 to 4 series-connected white LEDs commonly found in monochrome or small color LCD panels of feature phones, PDAs, and handheld instruments.
- Keyboard Illumination : Drives LEDs for backlit keypads in mobile devices.
- Status Indicator Lighting : Provides controlled current for single or multiple white LED indicators for power, connectivity, or notification functions.
- Flashlight/Flash LED Drivers : Can be configured to drive a high-current LED for camera flash applications in some implementations, though its primary strength is in low-to-medium current backlighting.
### 1.2 Industry Applications
This component is predominantly deployed in cost-sensitive, space-constrained consumer electronics:
- Mobile Handsets (Feature Phones & Entry-Level Smartphones) : For main and sub-display backlighting.
- Portable Media Players & GPS Devices : For screen illumination.
- Digital Cameras & Camcorders : For LCD panel and control button backlighting.
- Handheld Industrial Terminals & Medical Monitors : Where reliable, efficient LED driving is required in battery-operated equipment.
### 1.3 Practical Advantages and Limitations
Advantages:
* High Efficiency (up to ~92%) : Utilizes a 1.5x fractional charge pump mode, minimizing power loss compared to linear regulators, especially when battery voltage drops below the LED forward voltage requirement.
* Small Solution Footprint : Requires only four small external ceramic capacitors (two flying, one input, one output), minimizing PCB area.
* Excellent Current Matching : Typical 0.5% channel-to-channel matching ensures uniform LED brightness.
* Integrated Digital Interface : Simple 2-wire I²C-compatible interface allows for precise brightness control via 32-step logarithmic dimming and individual LED on/off control.
* Low Noise Operation : Charge pump switching frequency is typically 1 MHz, which is above the audible range and allows for the use of small capacitors.
* Protection Features : Includes built-in over-voltage protection, thermal shutdown, and LED open-circuit detection.
Limitations:
* Limited Output Current : Typically drives up to ~120mA total (e.g., 4 LEDs at 30mA each). Not suitable for high-power flash LED applications requiring >200mA.
* Fixed Charge Pump Ratio : The 1.5x mode is the only boost mode. It cannot achieve higher ratios (e.g., 2x), limiting its headroom when the input voltage is very low relative to the total LED forward voltage.
* LED Configuration : Designed for driving LEDs in a series configuration. Driving LEDs in parallel without external ballast resistors is not recommended due to potential current imbalance.
* Legacy Component : As a part originally from Fairchild, it may be considered for legacy designs or specific cost-driven new designs, with potential newer alternatives available from ON Semiconductor.
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## 2. Design Considerations
### 2.1 Common Design Pitfalls and Solutions
| Pitfall | Consequence | Solution |
| :--- | :--- | :--- |
| Incorrect Capacitor Selection | Reduced efficiency, increased output ripple, instability. | Use X5R or X7R ceramic capacitors with low ESR. Adhere strictly to the
