EVL6562A-LED STMicroelectronics

AN2983 Application note Constant current inverse buck LED driver using L6562A Introduction Whenever a lighting application, such as street lighting for example, requires an elevated number of LEDs, there are basically two solutions: the first is to connect all the diodes in series in a singlestrin the second is to place several strings in parallel with fewer elements in each one. The first solution, even if simpler, poses stringent safety requirements due to the high supply voltage. The latter needs a lower input voltage but the current through each string has to be independently controlled. Since, from a system point of view, the second solution seems more viable, we have developed an application to investigate the possibility of employing an L6562A to implement such a constant current controller. This document describes the EVL6562A-LED demonstration board and summarizes the relevant results obtained. Figure 1. EVL6562A-LED: L6562A constant current inverse buck driver module - V December 2009 Doc ID 15679 Rev 1 1/32 www.st.com Contents AN2983 Contents 1 Main characteristics . 4 1.1 System configuration . 4 1.2 Requirements . 4 1.3 Interface . 5 2 Circuit description . 6 2.1 Power section . 6 2.2 L6562A controller 8 2.3 FOT (fixed off time) delay circuit . 9 2.4 Current setting . 11 2.5 LED number compensation . 15 2.6 Shutdown/dimming 18 2.7 Auxiliary power . 21 2.8 Open-/short-circuit protection 22 3 Measurements . 24 3.1 LED voltage dependency . 24 3.2 Input voltage dependency 26 4 Electrical schematic and bill of materials . 27 5 References 30 6 Revision history . 31 2/32 Doc ID 15679 Rev 1