Product Overview
The STMicroelectronics ALED7707 is a high-efficiency, constant-current LED driver designed to power multiple white LEDs arranged in a series configuration. It integrates a current-mode step-up (boost) DC-DC controller optimized for backlighting applications in LCD displays, particularly in automotive, industrial, and general-purpose lighting systems. The device is capable of driving up to 40 white LEDs with high accuracy and flexibility while incorporating robust protection and fault-detection features.
Key Features and Functions
* Step-up (boost) DC-DC controller
* Drives up to 10 strings of LEDs with independent PWM dimming control
* Output voltage up to 36 V
* Precision current control with ±2% LED current matching
* External MOSFET control for flexibility and power efficiency
* I²C interface for configuration and diagnostics
* Fault detection (open LED, shorted LED, overvoltage, overtemperature, etc.)
* Synchronization with external clock
* Spread spectrum modulation for EMI reduction
Electrical Specifications
* Input Voltage Range: 4.5 V to 36 V
* Output Voltage: Up to 36 V, depending on external components and configuration
* Switching Frequency: Adjustable from 100 kHz to 1 MHz
* LED Current Matching Accuracy: ±2% typical across channels
* Feedback Voltage Reference: 200 mV typical
* Quiescent Current: 5 mA (typical, at no switching)
* Shutdown Current: <10 µA (typical)
* Operating Temperature Range: -40°C to +125°C
* MOSFET Drive Capability: Compatible with external N-channel MOSFETs
Architecture and Control
The ALED7707 operates as a current-mode boost controller where an external power MOSFET is driven by the device’s integrated gate driver. A current-sense resistor monitors the inductor current for precise control and peak current-mode regulation. The feedback loop regulates the LED current indirectly by sensing the voltage across dedicated current-sink pins.
LED channels are controlled with individual Pulse Width Modulation (PWM) inputs, allowing separate dimming for each string. The PWM signals can be asynchronous or synchronized using an external clock input, which helps prevent interference patterns and reduce EMI.
I²C Interface and Digital Configuration
The ALED7707 includes a built-in I²C interface enabling real-time configuration and diagnostics. Through this interface, users can:
* Adjust the LED current levels
* Set or override the PWM dimming duty cycle
* Monitor open/short circuit faults
* Access thermal status and fault registers
* Perform calibration or manufacturing test sequences
Dimming Capabilities
* PWM Dimming: Each of the 10 channels has an independent PWM input for dimming control, offering high flexibility in brightness adjustment.
* Analog Dimming via I²C: Current levels can be digitally controlled for each channel for finer brightness modulation.
* Combined Dimming: For applications requiring wide dynamic range dimming, the ALED7707 supports a hybrid approach combining analog and PWM dimming.
Protection and Reliability Features
* Open LED Detection: Automatically detects and isolates open string to prevent malfunction of the entire system.
* Short LED Detection: Identifies shorted LEDs to maintain protection for other strings.
* Overvoltage Protection: Monitors and clamps the output to prevent excessive voltage build-up.
* Overtemperature Protection: Includes internal thermal shutdown circuitry to safeguard the device.
* Soft Start: Prevents inrush currents and overshoots during power-up.
* Current Limiting: Built-in current limit for the external FET to ensure safe operation.
Application Areas
* Automotive LCD backlighting (cluster, infotainment, HUD)
* Industrial panel illumination
* Large-size display backlighting (TVs, monitors)
* General-purpose white LED drivers for multiple-channel lighting systems
* Signage and architectural lighting where individual channel dimming is needed
Package and Mechanical Characteristics
* Package Type: TQFP48 (Thin Quad Flat Package)
* Pin Count: 48
* Thermal Resistance (Junction-to-Ambient): Typically 45 °C/W
* Mounting Type: Surface-mount, suitable for automated PCB assembly
Design Flexibility
The ALED7707 allows high customization through external component selection, such as inductors and FETs, to balance cost, efficiency, and board area. With flexible dimming, robust protections, and a digital control interface, it suits complex systems where high reliability and configurability are crucial.
Summary
STMicroelectronics ALED7707 is a highly versatile and feature-rich LED driver controller ideal for demanding applications requiring multi-channel control, high precision current regulation, and robust protection. It supports automotive-grade performance, fine dimming control, and real-time digital configuration, making it well-suited for both static and dynamic backlight or lighting systems.
