参数资料
型号: SP6683ER-L
厂商: Exar Corporation
文件页数: 11/14页
文件大小: 0K
描述: IC LED DRIVER WHITE 10DFN
标准包装: 121
拓扑: PWM,切换式电容器(充电泵)
输出数: 1
内部驱动器:
类型 - 主要: 背光,闪灯/白光
类型 - 次要: 白色 LED
频率: 700kHz ~ 1.5MHz
电源电压: 2.7 V ~ 5.5 V
安装类型: 表面贴装
封装/外壳: 10-VFDFN 裸露焊盘
供应商设备封装: 10-DFN(3x3)
包装: 散装
工作温度: -40°C ~ 85°C
APPLICATION INFORMATION
Brightness Matching
For white LEDs, the forward voltage drop is a
function of the operating current. However, for
a given current, the forward voltage drop across
each LED does not always match exactly. This
can cause uneven brightness in the white LEDs.
In the figure below, assuming high-precision
bias resistors were used, the operating current
ratio of two different branches can be easily
derived as shown by:
used. This could be done by using a larger
resistor, as shown in the figure below. Rb2 is
used to bias the operating current of the white
LED, Rb1 is use to increase the output voltage.
Better brightness matching was achieved at the
cost of the power wasted on the bias resistor.
Power Efficiency
The efficiency of driving the white LEDs can be
I 1
V OUT - V F1
=
I 2 V OUT - V F2
where I 1 & I 2 are the operating current of the
white LEDs, where V F1 & V F2 are the forward
voltage of the white LEDs.
calculated by
η = V F ? I F =
V i ? I i
Where
V F ? I F
V i ? (n ? I F + I Q )
V F
V i ? n
V i & I i are input voltage and current;
Since the brightness of the white LED is propor-
tional to the operating current, for better bright-
ness matching, a higher output voltage could be
V F & I F are the forward voltage and operating
current of the White LED;
I Q is quiescent current, which is considered
small compared with I F .
V OUT
1
I 1
I 2
D1
VF1
D2
VF2
I n
Dn
VFn
SP6683
Rb1
GND
8
V FB
5
Rb2
Rb
Rb
Rb
Improving brightness matching
Date: 3/31/06 RevG
SP6683 1X/1.5X Charge Pump LED Driver for Flash or Backlight
11
? Copyright 2006 Sipex Corporation
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