AN2129 is an application note about L6902D based DC/DC converter, which introduces the dimming method for LED light.
The document explains two basic principles for controlling LED light output: analog current control and average current control by Pulse Width Modulation (PWM). It details how to implement these methods using the L6902D switching regulator.
An application board design is presented, featuring a single dimming input connector usable for both analog (0-3.3V) and PWM (3.3V or 5V) control. The note includes schematic diagrams, PCB layout details, a bill of materials, resistor calculation equations, and efficiency measurement results.
The converter provides up to 1A output current with an accuracy of 5%.
When the dimming pin is grounded, the maximum output current provided is 350mA.
The current is switched with a frequency higher than 100Hz to avoid flickering.