收藏本站
LT3491
APPLICATIO S I FOR ATIO
The time it takes for the LED current to reach its pro-
grammed value sets the achievable dimming range for a
given PWM frequency. For example, the settling time of
the LED current in Figure 7 is approximately 30 μ s for a 3V
input voltage. The achievable dimming range for this
application and 100Hz PWM frequency can be determined
using the following method.
Example:
? = 100 Hz , t SETTLE = 30 μs
down to 100mV. The use of both techniques together
allows the average LED current for the four LED applica-
tion to be varied from 20mA down to less than 20 μ A.
Figure 9 shows the application for dimming using both
analog dimming and PWM dimming. A potentiometer
must be added to ensure that the gate of the NMOS
receives a logic-level signal, while the CTRL signal can be
adjusted to lower amplitudes.
= = 0 . 01 s
t PERIOD =
1 1
? 100
1kHz
100Hz
D im Range = = = 300 : 1
t SETTLE
t PERIOD 0 . 01 s
30 μs
10kHz
Min Duty Cycle =
t SETTLE
t PERIOD
? 100 =
30 μs
0 . 01 s
? 1000 = 0 . 3 %
1
10
100
1000
Duty Cycle Range = 100 % → 0 . 3 % at 100 Hz
PWM DIMMING RANGE
3491 F08
The calculations show that for a 100Hz signal the dimming
range is 300 to 1. In addition, the minimum PWM duty
cycle of 0.3% ensures that the LED current has enough
V IN
Figure 8. Dimming Range Comparison
of Three PWM Frequencies
time to settle to its final value. Figure 8 shows the dimming
range achievable for three different frequencies with a
settling time of 30 μ s.
The dimming range can be further extended by changing
3V TO 5V
L1
10 μ H
C1
1 μ F
SW
V IN
LT3491
CAP
R SENSE
10 ?
the amplitude of the PWM signal. The height of the PWM
GND
LED
signal sets the commanded sense voltage across the
sense resistor through the CTRL pin. In this manner both
analog dimming and direct PWM dimming extend the
CTRL
2.5V
PWM
FREQ
C2
1 μ F
dimming range for a given application. The color of the
LEDs no longer remains constant because the forward
current of the LED changes with the height of the CTRL
signal. For the four LED application described above, the
LEDs can be dimmed first, modulating the duty cycle of the
PWM signal. Once the minimum duty cycle is reached, the
height of the PWM signal can be decreased below 1.5V
0V
Q1
Si2302
100k
3491 F09
Figure 9. Li-Ion to Four White LEDs with Both
PWM Dimming and Analog Dimming
3491fa
10
发布紧急采购，3分钟左右您将得到回复。

采购需求

(若只采购一条型号，填写一行即可)

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

发布成功！您可以继续发布采购。也可以进入我的后台，查看报价

*型号 *数量 厂商 批号 封装
添加更多采购

我的联系方式

*
*
*
相关PDF资料
LT3492IFE#TRPBF IC LED DVR HP CONST CURR 28TSSOP
LT3496IUFD#PBF IC LED DRVR WHT/RGB BCKLT 28-QFN
LT3497EDDB#TRMPBF IC LED DRIVR WHITE BCKLGT 10-DFN
LT3498EDDB#TRPBF IC LED DRVR WT/OLED BCKLGT 12DFN
LT3517HUF#PBF IC LED DRIVER AUTOMOTIVE 16-QFN
LT3519EMS-2#PBF IC LED DRVR HP CONST CURR 16MSOP
LT3590ESC8#TRMPBF IC LED DRVR WHITE BCKLGT SC-70-8
LT3591EDDB#TRMPBF IC LED DRIVER WHITE BCKLGT 8-DFN
相关代理商/技术参数
LT3491EDC#TRPBF 功能描述:IC LED DRIVER WHITE BCKLGT 6-DFN 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 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
LT3492 制造商:LINER 制造商全称:Linear Technology 功能描述:60V Triple Step-Down LED Driver Programmable Temperature Protection
LT3492EFE 制造商:LINER 制造商全称:Linear Technology 功能描述:Triple Output LED Driver with 3000:1 PWM Dimming