350mA驱动7W LED芯片介绍

当驱动LED电源小于6V，输出最大350 mA给LED时，设备输出1W。通过使用buck稳压器而不是线性稳压器架构，设备可达最大94%的效率。Catalyst使用高性能高压CMOS技术制造器件，取保器件能够经受瞬间40V输入。简单的管脚提供变暗和控制功能。

　　设计者依靠电路中电感，而不是电阻电容比确定芯片转换频率。器件允许电感中没有电流，所以器件通常工作在间断模式。由于器件再次工作前电流近似为0，所以电路峰值为平均电流的两倍。这个特性允许电阻设置峰值电流，进而确定平均电流。使用电感值较小的电感比大电感，使得工作电流上升和下降的更快，导致对给定输入电压更快的工作频率。使用这个方法，可以设置转换频率范围为50kHz到1MHz。实际上，33μH的电感在很宽的输入电压范围内提供350mA驱动电流。“器件检测到电感电流为0A时，器件处于连续或间断工作的临界状态”，Catalyst公司功率管理产品主管Anthony Russ

ell说：“频率由电感值和供电电压确定”。CAT4201有ROHS（有害成分限制）TSOT-23-5封装和价格为72 cents（10,000片）。可提供开发板。

　　英文原文：

　　7W LED-driver IC provides 350 mA

　　By Paul Rako, Technical Editor -- EDN, 10/11/2007

　　Targeting use in tunnel-lighting, automotive-lighting, and similar applications, the new Catalyst Semiconductor CAT4201 buck-regulator driver can deliver 7W of Power to a string of white LEDs operating from a 24V rail. The device delivers 1W when driving an LED off a 6V rail and delivers as much as 350 mA to the LED. By using a buck-regulator architecture rather than linear-regulator architecture, the device achieves efficiency as high as 94%. Catalyst manufactures the device using a high-performance, high-voltage CMOS process so that it can withstand 40V transients on the input. A single pin provides dimming and control.

A designer establishes the chip’s switching frequency, which depends on the value of the inductor in the circuit rather than the resistor-to-capacitor ratio. The device allows the inductor to run out of current, so it always operates just into the discontinuous mode. The peak current is twice the average current because the current goes to exactly 0A before the part turns on again. This feature allows a resistor that sets the peak current to also establish the average current. Using low-value inductors causes the operating current to rise and fall faster than it would with high-value inductors, resulting in a faster operating frequency for a given input voltage. Using this method, you can set the switching frequency at 50 kHz to 1 MHz. In practice, an inductor value of 33 μH provides a 350-mA drive current across a wide range of input voltages. “The part detects when the inductor current goes to 0A and therefore can operate at the crossover point between continuous and discontinuous operation,” says Anthony Russell, Catalyst’s director of Power-management products. “The frequency depends on the inductor value and the supply voltage.” The CAT4201 is available in a RO

HS (reduction-of-hazardous-substances) TSOT-23-5 package and sells for 72 cents (10,000). A demo board is available.

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