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| 型号： | LM2795TLX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 11/23页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR WHT BCKLT 14USMD |
| 标准包装： | 3,000 |
| 恒定电流： | 是 |
| 拓扑： | PWM，切换式电容器（充电泵） |
| 输出数： | 4 |
| 内部驱动器： | 是 |
| 类型 - 主要： | 背光 |
| 类型 - 次要： | 白色 LED |
| 频率： | 325kHz ~ 515kHz |
| 电源电压： | 2.7 V ~ 5.5 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 14-WFBGA |
| 供应商设备封装： | 14-TuSMD |
| 包装： | 带卷 (TR) |
| 工作温度： | -30°C ~ 85°C |
| 配用： | LM2795EVAL-ND - BOARD EVALUATION LM2795 |
| 其它名称： | LM2795TLX |
SNVS168L – JANUARY 2002 – REVISED MAY 2013
For most applications, ceramic capacitors with X7R or X5R temperature characteristic are preferred for use with
the LM2794/5. These capacitors have tight capacitance tolerance (as good as ±10%), hold their value over
temperature (X7R: ±15% over ? 55°C to 125°C; X5R: ±15% over ? 55°C to 85°C), and typically have little voltage
coefficient. Capacitors with Y5V or Z5U temperature characteristic are generally not recommended for use with
the LM2794/5. Capacitors with these temperature characteristics typically have wide capacitance tolerance
(+80%, ? 20%), vary significantly over temperature (Y5V: +22%, ? 82% over ? 30°C to +85°C range; Z5U: +22%,
? 56% over +10°C to +85°C range), and have poor voltage coefficients. Under some conditions, a nominal 1μF
Y5V or Z5U capacitor could have a capacitance of only 0.1μF. Such detrimental deviation is likely to cause Y5V
and Z5U capacitors to fail to meet the minimum capacitance requirements of the LM2794/5. Table 1 lists
suggested capacitor suppliers for the typical application circuit.
Table 1. Ceramic Capacitor Manufacturers
Manufacturer
TDK
Murata
Taiyo Yuden
Contact
LED SELECTION
The LM2794/5 is designed to drive LEDs with a forward voltage of about 3.0V to 4.0V. The typical and maximum
diode forward voltage depends highly on the manufacturer and their technology. Table 2 lists two suggested
manufacturers. Forward current matching is assured over the LED process variations due to the constant current
output of the LM2794/5.
Table 2. White LED Selection
Manufacturer
Osram
Nichia
Contact
I SET AND BRGT PINS
An external resistor, R SET , is connected to the I SET pin to set the current to be mirrored in each of the LED
outputs. The internal current mirror sets each LED output current with a 10:1 ratio to the current through R SET .
The current mirror circuitry matches the current through each LED to within 0.5%.
In addition to R SET , a voltage may be applied to the V BRGT pin to vary the LED current. By adjusting current with
the Brightness pin (BRGT), the brightness of the LEDs can be smoothly varied.
Applying a voltage on BRGT between 0 to 3 volts will linearly vary the LED current. Voltages above 3V do not
increase the LED current any further. The voltage on the V BRGT pin is fed into an internal resistor network with a
ratio of 0.385. The resulting voltage is then summed with a measured offset voltage of 0.188V, which comes
from the reference voltage being fed through a resistor network (See Functional Block Diagram ). The brightness
control circuitry then uses the summed voltage to control the voltage across R SET . An equation for approximating
the LED current is:
I LED = ¨
?
¨
? ? * MirrorRati o
§ V OFFSET + V BRGT * 0 . 385
R SET
·
1
I LED = ¨
?
¨
? ? *
1
§ 0 .188 + V BRGT * 0 . 385
R SET
· 10
1
Amps
I LED CURRENT SELECTION PROCEDURES
The following procedures illustrate how to set and adjust output current levels. For constant brightness or analog
brightness control, go to “Brightness control using BRGT”. Otherwise refer to “Brightness control using PWM”.
Brightness Control Using PWM
1. Set the BRGT pin to 0V.
Copyright ? 2002–2013, Texas Instruments Incorporated
Product Folder Links: LM2794 LM2795
11
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| LM27961TL/NOPB | 功能描述:IC LED DRVR WHT BCKLT 18USMD RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 标准包装:1 系列:- 恒定电流:- 恒定电压:- 拓扑:PWM，切换式电容器（充电泵） 输出数:1 内部驱动器:是 类型 - 主要:背光 类型 - 次要:白色 LED 频率:642kHz 电源电压:2.7 V ~ 5.5 V 输出电压:5V 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-VSON 包装:剪切带 (CT) 工作温度:-30°C ~ 85°C 产品目录页面:1371 (CN2011-ZH PDF) 其它名称:BD1603NUV-E2CT |
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