原标题：ST STCS1A 恒流高亮LED参考设计方案

　　ST公司的STCS1A 是一款可变输入电压源提供精确BiCMOS工艺恒流源。主要用于5V、12V和24V LED驱动器替代分立元件解决方案，具有高精确性、高集成性和高可靠性特点。恒流可通过一个外部电阻进行调节，最大输出电流为1.5A(正负10%精度)，可通过专用引脚执行PWM进行调光控制。可通过外部电容电流上升斜率，以减少EMI影响。本文首先介绍芯片的简介、特性、内部框图及应用领域，并给出相应设计方案的设计原理图、元器件列表及PCB元件布局图。

　　The STCS1A is a BiCMOS constant current source designed to provide a precise constant current starting from a varying input voltage source. The main target is to replace discrete components solution for driving LEDs in low voltage applications such as 5 V, 12 V or 24 V giving benefits in terms of precision, integration and reliability.

　　The current is set with external resistor up to 1.5 A with a ± 10 % precision; a dedicated pin allows implementing PWM dimming. An external capacitor allows setting the slope for the current rise from tens of microseconds to tens of milliseconds allowing reduction of EMI.

　　An open-drain pin output provides information on load disconnection condition.

　　STCS1A主要特性：

　　■ Up to 40 V input voltage

　　■ Less than 0.5 V voltage overhead

　　■ Up to 1.5 A output current

　　■ PWM dimming pin

　　■ Shutdown pin

　　■ LED disconnection diagnostic

　　■ Slope control with external cap

　　STCS1A应用：

　　■ LED constant current supplying for varying input voltages

　　■ Low voltage lighting

　　■ Small appliances LED lighting

　　■ Car LED lights

　　图1. STCS1A内部方框图

　　STCS1A方案介绍：

　　The recent improvements in high power light-emitting diode (LED) technology with 100 lumens per LED chip and efficiency higher than that of incandescent lamps bring solid state lighting close to reality. Light-emitting diodes (LEDs) have become very popular in the area of general lighting as a replacement technology for low voltage lighting. Customers are recognizing the advantages of using LED lighting which include long operating life, no fragile glass, and low voltage DC operated.

　　LEDs are now available in higher and higher wattages per package (1 W, 3 W and 5 W) with currents up to 1.5 A. At these current levels, the traditional means of limiting current with a resistor are not sufficiently accurate nor efficient. It is well known that the brightness of LEDs is proportional to the forward current. The best way to supply LEDs is to control the forward current in order to get a good match of the output light. LED manufacturers specify the characteristics (such as lumens, beam pattern, color) of their devices at a specified forward current (IF) but they do not specify these characteristics at a specific forward voltage (VF). In order to better control the LED current under several application conditions, STMicroelectronics has developed the STCS1, a device which not only guarantees a constant LED current but also provides useful features that make the device suitable for different applications such as advertising signs, automotive interior and exterior lighting, and emergency vehicle warning lights. This document describes how to use the STCS1 evaluation board. It includes a schematic diagram, bill of materials (BOM), and test data.

STCS1A方案原理图：

　　图2. STCS1A方案原理图

　　STCS1A方案材料清单：

　　PCB元件布局图：