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| 型号： | LM3421MHX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 25/67页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR HP CONS CURR 16TSSOP |
| 产品培训模块： | LED Design Solutions |
| 标准包装： | 2,500 |
| 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： | 带卷 (TR) |
| 工作温度： | -40°C ~ 125°C |
| 其它名称： | LM3421MHX |
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SNVS574E – JULY 2008 – REVISED MAY 2013
In general, Δ i LED-PP is recommended by manufacturers to be less than 40% of the average LED current (I LED ).
Therefore, for the buck regulator with no output capacitance, Δ i L-PP should also be less than 40% of I LED . For the
boost and buck-boost topologies, Δ i L-PP can be much higher depending on the output capacitance value.
However, Δ i L-PP is suggested to be less than 100% of the average inductor current (I L ) to limit the RMS inductor
current.
L1 is also suggested to have an RMS current rating at least 25% higher than the calculated minimum allowable
RMS inductor current (I L-RMS ).
LED DYNAMIC RESISTANCE
When the load is a string of LEDs, the output load resistance is the LED string dynamic resistance plus R SNS .
LEDs are PN junction diodes, and their dynamic resistance shifts as their forward current changes. Dividing the
forward voltage of a single LED (V LED ) by the forward current (I LED ) leads to an incorrect calculation of the
dynamic resistance of a single LED (r LED ). The result can be 5 to 10 times higher than the true r LED value.
Figure 34. Dynamic Resistance
Obtaining r LED is accomplished by refering to the manufacturer's LED I-V characteristic. It can be calculated as
the slope at the nominal operating point as shown in Figure 34 . For any application with more than 2 series
LEDs, R SNS can be neglected allowing r D to be approximated as the number of LEDs multiplied by r LED .
OUTPUT CAPACITOR
For boost and buck-boost regulators, the output capacitor (C O ) provides energy to the load when the recirculating
diode (D1) is reverse biased during the first switching subinterval. An output capacitor in a buck topology will
simply reduce the LED current ripple ( Δ i LED-PP ) below the inductor current ripple ( Δ i L-PP ). In all cases, C O is sized
to provide a desired Δ i LED-PP . As mentioned in the INDUCTOR section, Δ i LED-PP is recommended by
manufacturers to be less than 40% of the average LED current (I LED-PP ).
C O should be carefully chosen to account for derating due to temperature and operating voltage. It must also
have the necessary RMS current rating. Ceramic capacitors are the best choice due to their high ripple current
rating, long lifetime, and good temperature performance. An X7R dieletric rating is suggested.
INPUT CAPACITORS
The input capacitance (C IN ) provides energy during the discontinuous portions of the switching period. For buck
and buck-boost regulators, C IN provides energy during t ON and during t OFF , the input voltage source charges up
C IN with the average input current (I IN ). For boost regulators, C IN only needs to provide the ripple current due to
the direct connection to the inductor. C IN is selected given the maximum input voltage ripple ( Δ v IN-PP ) which can
be tolerated. Δ v IN-PP is suggested to be less than 10% of the input voltage (V IN ).
An input capacitance at least 100% greater than the calculated C IN value is recommended to account for derating
due to temperature and operating voltage. When PWM dimming, even more capacitance can be helpful to
minimize the large current draw from the input voltage source during the rising transistion of the LED current
waveform.
Copyright ? 2008–2013, Texas Instruments Incorporated
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Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1
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相关代理商/技术参数 |
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|---|---|
| LM3421Q0 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:N-Channel Controllers for Constant Current LED Drivers |
| LM3421Q0MH | 制造商:NSC 制造商全称:National Semiconductor 功能描述:N-Channel Controllers for Constant Current LED Drivers |
| LM3421Q0MH/NOPB | 功能描述:LED照明驱动器 RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N |
| LM3421Q0MHNOPB | 制造商:National Semiconductor 功能描述:LED DRVR 5V/9V/12V/15V/18V/24V 16-Pin TSSOP EP Tube |
| LM3421Q0MHX | 制造商:NSC 制造商全称:National Semiconductor 功能描述:N-Channel Controllers for Constant Current LED Drivers |
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