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| 型号： | LT3491EDC#TRMPBF |
| 厂商： | Linear Technology |
| 文件页数： | 9/16页 |
| 文件大小： | 0K |
| 描述： | IC LED DRIVER WHITE BCKLGT 6-DFN |
| 标准包装： | 1 |
| 拓扑： | PWM，升压（升压） |
| 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： | 1.8MHz ~ 2.8MHz |
| 电源电压： | 2.5 V ~ 12 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 6-WFDFN 裸露焊盘 |
| 供应商设备封装： | 6-DFN-EP（2x2） |
| 包装： | 标准包装 |
| 工作温度： | -40°C ~ 85°C |
| 产品目录页面： | 1339 (CN2011-ZH PDF) |
| 其它名称： | LT3491EDC#TRMPBFDKR |
LT3491
APPLICATIO S I FOR ATIO
Using a Filtered PWM Signal
A filtered PWM signal can be used to control the bright-
ness of the LED string. The PWM signal is filtered (Figure
5) by a RC network and fed to the CTRL pin.
The corner frequency of R1, C1 should be much lower than
the frequency of the PWM signal. R1 needs to be much
smaller than the internal impedance of the CTRL pin which
is 10M ? (typ).
level Si2302 MOSFET can be used since its source is
connected to ground. The PWM signal is applied to the
CTRL pin of the LT3491 and the gate of the MOSFET. The
PWM signal should traverse between 0V to 2.5V, to ensure
proper turn on and off of the driver and the NMOS
transistor Q1. When the PWM signal goes high, the LEDs
are connected to ground and a current of I LED = 200mV/
R SENSE flows through the LEDs. When the PWM signal
goes low, the LEDs are disconnected and turn off. The
MOSFET ensures that the LEDs quickly turn off without
discharging the output capacitor which in turn allows the
PWM
10kHz TYP
R1
100k
C1
0.1 μ F
LT3491
CTRL
3491 F05
LEDs to turn on faster. Figure 7 shows the PWM dimming
waveforms for the circuit in Figure 6.
V IN
3V TO 5V
Figure 5. Dimming Control Using a Filtered PWM Signal
L1
10 μ H
SW
V IN
CAP
Direct PWM Dimming
Changing the forward current flowing in the LEDs not only
changes the intensity of the LEDs, it also changes the
color. The chromaticity of the LEDs changes with the
C1
1 μ F
GND
LT3491
CTRL
LED
R SENSE
10 ?
C2
1 μ F
change in forward current. Many applications cannot
tolerate any shift in the color of the LEDs. Controlling the
intensity of the LEDs with a direct PWM signal allows
dimming of the LEDs without changing the color. In
2.5V
0V
PWM
FREQ
100k
Q1
Si2302
addition, direct PWM dimming offers a wider dimming
range to the user.
Dimming the LEDs via a PWM signal essentially involves
turning the LEDs on and off at the PWM frequency. The
typical human eye has a limit of ~60 frames per second. By
increasing the PWM frequency to ~80Hz or higher, the eye
will interpret that the pulsed light source is continuously on.
Additionally, by modulating the duty cycle (amount of “on-
time”), the intensity of the LEDs can be controlled. The color
of the LEDs remains unchanged in this scheme since the
LED current value is either zero or a constant value.
Figure 6 shows a Li-Ion powered driver for four white
3491 F06
Figure 6. Li-Ion to Four White LEDs with Direct PWM Dimming
I LED
20mA/DIV
I L
200mA/DIV
PWM
5V/DIV
LEDs. Direct PWM dimming method requires an external
NMOS tied between the cathode of the lowest LED in the
V IN = 3V
4 LEDs
2ms/DIV
3491 F07
string and ground as shown in Figure 6. A simple logic
Figure 7. Direct PWM Dimming Waveforms
3491fa
9
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相关代理商/技术参数 |
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| LT3491ESC8 | 制造商:Linear Technology 功能描述:LED DRVR 6Segment 3.3V/5V/9V 8-Pin SC-70 |
| LT3491ESC8#PBF | 制造商:Linear Technology 功能描述:LED DRVR 6Segment 3.3V/5V/9V 8-Pin SC-70 制造商:Linear Technology 功能描述:LED DRIVER 2.5-12V 2.3MHZ 5 |
| LT3491ESC8#TR | 制造商:Linear Technology 功能描述:LED DRVR 6Segment 3.3V/5V/9V 8-Pin SC-70 T/R |
| LT3491ESC8#TRMPBF | 功能描述:IC LED DRVR WHITE BCKLGT SC-70-8 RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 标准包装:6,000 系列:- 恒定电流:- 恒定电压:- 拓扑:开路漏极，PWM 输出数:4 内部驱动器:是 类型 - 主要:LED 闪烁器 类型 - 次要:- 频率:400kHz 电源电压:2.3 V ~ 5.5 V 输出电压:- 安装类型:表面贴装 封装/外壳:8-VFDFN 裸露焊盘 供应商设备封装:8-HVSON 包装:带卷 (TR) 工作温度:-40°C ~ 85°C 其它名称:935286881118PCA9553TK/02-TPCA9553TK/02-T-ND |
| LT3491ESC8#TRPBF | 功能描述:IC LED DRVR WHITE BCKLGT SC-70-8 RoHS:是 类别:集成电路 (IC) >> PMIC - LED 驱动器 系列:- 标准包装:6,000 系列:- 恒定电流:- 恒定电压:- 拓扑:开路漏极，PWM 输出数:4 内部驱动器:是 类型 - 主要:LED 闪烁器 类型 - 次要:- 频率:400kHz 电源电压:2.3 V ~ 5.5 V 输出电压:- 安装类型:表面贴装 封装/外壳:8-VFDFN 裸露焊盘 供应商设备封装:8-HVSON 包装:带卷 (TR) 工作温度:-40°C ~ 85°C 其它名称:935286881118PCA9553TK/02-TPCA9553TK/02-T-ND |
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