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| 型号： | LM3421Q1MH/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 22/67页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR HP CONS CURR 16TSSOP |
| 标准包装： | 92 |
| 系列： | PowerWise® |
| 恒定电流： | 是 |
| 拓扑： | PWM，SEPIC，降压（降压），升压（升压） |
| 输出数： | 1 |
| 内部驱动器： | 无 |
| 类型 - 主要： | 车载 |
| 类型 - 次要： | 高亮度 LED（HBLED） |
| 频率： | 2MHz |
| 电源电压： | 4.5 V ~ 75 V |
| 输出电压： | 3 V ~ 72 V |
| 安装类型： | 表面贴装 |
| 封装/外壳： | 16-TSSOP（0.173"，4.40mm）裸露焊盘 |
| 供应商设备封装： | 16-TSSOP-EP |
| 包装： | 管件 |
| 工作温度： | -40°C ~ 125°C |
| 产品目录页面： | 1284 (CN2011-ZH PDF) |
| 其它名称： | LM3421Q1MH |
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SNVS574E – JULY 2008 – REVISED MAY 2013
The series dimFET will open the LED load, when nDIM is low, effectively speeding up the rise and fall times of
the LED current. Without any dimFET, the rise and fall times are limited by the inductor slew rate and dimming
frequencies above 1 kHz are impractical. Using the series dimFET, dimming frequencies up to 30 kHz are
achievable. With a parallel dimFET (buck topology), even higher dimming frequencies are achievable.
When using the PWM functionality in a boost regulator, the PWM signal can drive a ground referenced FET.
However, with buck-boost and buck topologies, level shifting circuitry is necessary to translate the PWM dim
signal to the floating dimFET as shown in Figure 30 and Figure 31 . If high side dimming is necessary in a boost
regulator using the LM3423, level shifting can be added providing the polarity inverting DPOL pin is pulled low
When using a series dimFET to PWM dim the LED current, more output capacitance is always better. A general
rule of thumb is to use a minimum of 40 μF when PWM dimming. For most applications, this will provide
adequate energy storage at the output when the dimFET turns off and opens the LED load. Then when the
dimFET is turned back on, the capacitance helps source current into the load, improving the LED current rise
time.
A minimum on-time must be maintained in order for PWM dimming to operate in the linear region of its transfer
function. Because the controller is disabled during dimming, the PWM pulse must be long enough such that the
energy intercepted from the input is greater than or equal to the energy being put into the LEDs. For boost and
buck-boost regulators, the minimum dimming pulse length in seconds (t PULSE ) is:
2 x I LED x V O X L1
t PULSE =
V IN 2
(32)
Even maintaining a dimming pulse greater than t PULSE , preserving linearity at low dimming duty cycles is difficult.
The second helpful modification is to remove the C FS capacitor and R FS resistor, eliminating the high frequency
compensation pole. This should not affect stability, but it will speed up the response of the CSH pin, specifically
at the rising edge of the LED current when PWM dimming, thus improving the achievable linearity at low dimming
duty cycles.
LED+
LM3421/23
10 :
5 k :
Q7
100 nF
Q2
V CC
Q6
Q4
R SNS
10V
500 :
100 pF
V IN
DDRV
Figure 30. Buck-boost Level-Shifted PWM Circuit
22
Copyright ? 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM3421Q1MHX | 制造商:NSC 制造商全称:National Semiconductor 功能描述:N-Channel Controllers for Constant Current LED Drivers |
| LM3421Q1MHX/NOPB | 功能描述:板上安装温度传感器 RoHS:否 制造商:Omron Electronics 输出类型:Digital 配置: 准确性:+/- 1.5 C, +/- 3 C 温度阈值: 数字输出 - 总线接口:2-Wire, I2C, SMBus 电源电压-最大:5.5 V 电源电压-最小:4.5 V 最大工作温度:+ 50 C 最小工作温度:0 C 关闭: 安装风格: 封装 / 箱体: 设备功能:Temperature and Humidity Sensor |
| LM3421-SEPICEV/NOPB | 功能描述:电源管理IC开发工具 LM3421-SEPIC EVAL BOARD RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| LM3423 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:N-Channel Controllers for Constant Current LED Drivers |
| LM3423_11 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:LM3423 Buck-Boost 2 Layer Evaluation Board evaluation board showcases most features |
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