收藏本站
LT3498
APPLICATIONS INFORMATION — LED DRIVER
Direct PWM Dimming
Changing the forward current ?owing in the LEDs not only
changes the intensity of the LEDs, it also changes the color.
The chromaticity of the LEDs changes with the 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 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 con-
tinuously 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
signal should traverse between 0V to 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 SENSE1 ?ows
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 LEDs to turn on
faster. Figure 6 shows the PWM dimming waveforms for
the circuit in Figure 5.
I LED
20mA/DIV
I L
200mA/DIV
PWM
5V/DIV
this scheme since the LED current value is either zero or
a constant value.
V IN = 3V
4 LEDs
2ms/DIV
3498 F06
Figure 5 shows a Li-Ion powered driver for four white
LEDs. Direct PWM dimming method requires an external
NMOS tied between the cathode of the lowest LED in the
string and ground as shown in Figure 5. A simple logic
level Si2304 MOSFET can be used since its source is con-
nected to ground. The PWM signal is applied to the CTRL1
Figure 6. Direct PWM Dimming Waveforms
pin of the LT3498 and the gate of the MOSFET. The PWM
V IN 3V TO 5V
80
75
V IN = 3.6V
4 LEDs
100Hz = PWM
C OUT1
1μF
R SENSE1
10Ω
CAP1 SW1
LED1
L1
15μH
C IN
1μH
V IN SW2 CAP2 V OUT2
LT3498
70
65
60
55
Q1
Si2304BDS
100k
CTRL1 GND1
5V
GND2
CTRL2
FB2
50
0
2
4
6 8 10 12 14 16 18 20
LED CURRENT (mA)
3498 F07
PWM
0V
3498 F05
Figure 7. PWM Dimming Ef?ciency
FREQ
Figure 5. Li-Ion to Four White LEDs
with Direct PWM Dimming
3498fa
12
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
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
LT3593ES6#TRMPBF IC LED DRIVR WHITE BCKLGT TSOT-6
LT3595AEUHH#TRPBF IC LED DRIVR WHITE BCKLGT 56-QFN
LT3595EUHH#TRPBF IC LED DRIVR WHITE BCKLGT 56-QFN
LT3596EUHG#PBF IC LED DVR 300MA ADJ 52-VQFN
相关代理商/技术参数
LT34-SC 制造商:THOMAS & BETTS 功能描述:
LT3500 制造商:World Products 功能描述:
LT3500EDD#PBF 功能描述:IC REG DL BUCK/LINEAR 12-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*
LT3500EDD#TRPBF 功能描述:IC REG DL BUCK/LINEAR 12-DFN RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*
LT3500EDD-PBF 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller
LT3500EDD-TRPBF 制造商:LINER 制造商全称:Linear Technology 功能描述:Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller
LT3500EMSE#PBF 功能描述:IC REG DL BUCK/LINEAR 16-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*
LT3500EMSE#TRPBF 功能描述:IC REG DL BUCK/LINEAR 16-MSOP RoHS:是 类别:集成电路 (IC) >> PMIC - 稳压器 - 线性 + 切换式 系列:- 标准包装:2,500 系列:- 拓扑:降压（降压）同步（3），线性（LDO）（2） 功能:任何功能 输出数:5 频率 - 开关:300kHz 电压/电流 - 输出 1:控制器 电压/电流 - 输出 2:控制器 电压/电流 - 输出 3:控制器 带 LED 驱动器:无 带监控器:无 带序列发生器:是 电源电压:5.6 V ~ 24 V 工作温度:-40°C ~ 85°C 安装类型:* 封装/外壳:* 供应商设备封装:* 包装:*