LED Driver with Adaptive Charge Pump DC/DC Converter# Technical Documentation: FAN5607HMPX
Manufacturer : FAIRCHILD SEMICONDUCTOR (now part of ON Semiconductor)
Component Type : Monolithic, Constant-Current, Step-Up DC/DC Converter for LED Drivers
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## 1. Application Scenarios
### Typical Use Cases
The FAN5607HMPX is a high-efficiency, fixed-frequency, step-up DC/DC converter specifically designed to drive series-connected white or blue LEDs with a constant current. Its primary use cases include:
* Backlighting for Small to Medium LCD Displays : Providing uniform, adjustable brightness for displays in portable electronics. A single device can typically drive 2 to 6 series-connected LEDs from a low-voltage input (e.g., a single Li-Ion cell).
* Keypad and Indicator Lighting : Illuminating buttons, icons, or status indicators in consumer devices where consistent light output and dimming control are required.
* Flashlight/Flash LED Drivers : Used in camera phones or dedicated flashlights where a high, pulsed current is needed for the LED flash, often with a separate, lower current for torch mode.
### Industry Applications
* Mobile Communications : Feature phones, smartphones, and portable communication devices for display and interface lighting.
* Portable Consumer Electronics : Digital cameras, portable media players, GPS units, and handheld gaming consoles.
* Industrial Handhelds : Scanners, meters, and portable test equipment requiring reliable, battery-powered display illumination.
### Practical Advantages and Limitations
Advantages:
* High Efficiency (>80%) : Utilizes a synchronous rectifier architecture (internal switch and synchronous rectifier), minimizing power loss and extending battery life in portable applications.
* Compact Solution : Requires minimal external components (inductor, input/output capacitors, feedback resistors), saving board space.
* Precise Current Regulation : Maintains consistent LED brightness by regulating current, not voltage, which is critical for uniform illumination and LED longevity.
* Integrated Dimming Control : Supports both analog (via `ADJ` pin voltage) and digital PWM (Pulse Width Modulation) dimming, offering flexible brightness control.
* Integrated Protection : Features include under-voltage lockout (UVLO), cycle-by-cycle current limit, and thermal shutdown.
Limitations:
* Limited Output Current/Voltage : Designed for driving a specific number of series LEDs (e.g., up to ~30V output). It is not suitable for high-power LED arrays or very high voltage strings.
* Fixed Switching Frequency : While simplifying EMI filter design, it offers less flexibility to optimize for specific noise-sensitive bands compared to variable-frequency architectures.
* Requires External Inductor : Selection and placement of the power inductor are critical for performance and efficiency.
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## 2. Design Considerations
### Common Design Pitfalls and Solutions
1. Pitfall: LED Flicker or Instability during Dimming.
* Cause: Improper PWM dimming signal characteristics (frequency, rise/fall time) or poor layout causing noise on the feedback (`FB`) or `ADJ` pins.
* Solution: Ensure the PWM signal has fast edges and a frequency above 100 Hz (typically 200 Hz to 25 kHz). Use a dedicated, clean ground for the dimming control circuitry. Place a small capacitor (e.g., 100 pF to 1 nF) close to the `FB` pin to filter high-frequency noise.
2. Pitfall: Poor Efficiency or Excessive Inductor Heating.
* Cause: Incorrect inductor selection (saturation current too low, DCR too high) or operating at excessive duty cycles near the minimum off-time limit.
* Solution: Select an inductor with a saturation current rating significantly
