CXLE8856 a set-up DC-DC converter that delivers a regulated output current. The device switches at a 1.0MHz constant frequency, allowing for the use of small value external inductor and ceramic

目录34B嘉泰姆

1.产品概述                       2.产品特点
3.应用范围                       4.下载产品资料PDF文档 
5.产品封装图</span>                     6.电路原理图</span>                   
7.功能概述                        8.相关产品34B嘉泰姆

一,产品概述(General Description)    34B嘉泰姆

   The CXLE8856 is a set-up DC-DC converter that delivers a regulated output current. The device switches at a 1.0MHz constant frequency, allowing for the
use of small value external inductor and ceramic capacitors.The CXLE8856 is targeted to be used for driving loads up to 1A from a two-cell alkaline battery.
    The LED current can be auto adjusted by internal smart module and programmed by the external current sense resistor, Rs,connected between the feedback pin (FB) and ground. A low 95mV(TYP.) feedback voltage reduces the power
loss in the Rs for better efficiency. With its internal 2A,100mΩ NMOS switch, the device can provide high efficiency even at heavy load. During the shutdown
mode, the feedback resistor Rs and the load are completely disconnected and the current consumption is reduced to 1uA.The CXLE8856 is available in the 6-lead
SOT-23-6L package.
二.产品特点(Features)34B嘉泰姆

LED Power Efficiency: up to 90%
Current Accuracy: 5%(Vin =3.6V to 1.8V
@Vf =3.7V)
Low Start-Up Voltage: 0.9V
Low Hold Voltage:0.75V
1MHz Switching Frequency
Uses small, Low Profile External Components
Low RDS(ON) : 100mΩ (TYP.)
Over Temperature Protection
Low Profile SOT-23-6L Package
三,应用范围 (Applications)34B嘉泰姆

White LED Torch (Flashlight)
White LED Camera Flash
DSC(Digital Still Camera)Flash
Cellular Camera Phone Flash
PDA Camera Flash
Camcorder Torch(Flashlight) Lamp
四.下载产品资料PDF文档 34B嘉泰姆

需要详细的PDF规格书请扫一扫微信联系我们，还可以获得免费样品以及技术支持</span>！</span>34B嘉泰姆

五</span>,产品封装图 (Package)34B嘉泰姆

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六.电路原理图</span>34B嘉泰姆

七,功能概述34B嘉泰姆

Inductor Selection
The CXLE8856 can use small value inductors due to its switching frequency of 1MHz. The value of inductor will focus in the range of 2.2uH to 4.7uH for most CXLE8856 applications. In typical high current white LED applications,it is recommended to use a 4.7uH inductor. The inductor should have low DCR (DC resistance) to minimize the IR power loss, and it requires a current rating of 2A to handle the peak inductor current without saturating. 
Capacitor Selection
An input capacitor is required to reduce the input ripple and noise for proper operation of the CXLE8856. For good input decoupling,  Low  ESR(equivalent  series  resistance) capacitors should be used at the input. At least 2.2uF input capacitor  is  recommended  for  most  applications. A minimum output capacitor value of 6.8uF is recommended under normal operating conditions, while a 10uF-22uF capacitor may be required for higher power LED current. A reasonable value of the output capacitor depends on the LED current. The ESR of the output capacitor is the important parameter to determine the output voltage ripple of the converter, so low ESR capacitors should be used at the output to reduce the output voltage ripple. The small size of ceramic capacitors is an excellent choice for CXLE8856 applications. The X5R and X7R types are preferred because they maintain capacitance over wide voltage and temperature ranges.
Diode Selection
It's indispensable to use a Schottky diode rated at 2A with the CXLE8856. Using a Schottky diode with a lower forward voltage drop is better to improve the power LED efficiency, and its voltage rating should be greater than the output voltage. In application, the ON Semiconductor MBRA210LT3G is recommended. 
LED Current Setting
The LED current is set by the single external Rs resistor connected to the FB pin as shown in the typical application circuit on page 1. The typical FB reference is internally regulated to 95mV(TYP.). The LED current is 95mV/Rs. It's recommended to use a 1% or better precision resistor for the better LED current accuracy.
The formula and table 1 for Rs selection are shown as follows:
Rs=95mV/ILED
PCB Layout Guidelines
For best performance of the CXLE8856, the following guidelines must be strictly followed. Input and Output capacitors should be placed close to the IC and connected to ground plane to reduce noise coupling.Keep the main current traces as possible as short and wide.SW node of DC-DC converter is with high frequency voltage swing. It should be kept at a small area.Place the feedback components as close as possible to the IC and keep away from the noisy devices.
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