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参数资料
| 型号： | LM3423MHBKBSTEV/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 22/67页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL BUCK BOOST LM3423 |
| 标准包装： | 1 |
| 系列： | PowerWise® |
| 电流 - 输出 / 通道： | 1A |
| 输出及类型： | 1，非隔离 |
| 输出电压： | 35V |
| 特点： | 可调光 |
| 输入电压： | 4.5 ~ 35 V |
| 已供物品： | 板 |
| 已用 IC / 零件： | LM3423 |
| 其它名称： | LM3423MHBKBSTEV |
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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 |
|---|---|
| LM3423MHBSTEVAL | 制造商:Texas Instruments 功能描述:N-Channel Controllers For Constant Current LED Drivers Evaluation Board |
| LM3423MHBSTEVAL/NOPB | 功能描述:BOARD EVAL BOOST FOR LM3423 RoHS:是 类别:编程器，开发系统 >> 评估板 - LED 驱动器 系列:PowerWise® 标准包装:1 系列:PowerWise® 电流 - 输出 / 通道:20mA 输出及类型:1，非隔离 输出电压:17V 特点:可调光 输入电压:2.7 ~ 5.5 V 已供物品:板 已用 IC / 零件:LM3508 相关产品:LM3508TLX-ND - IC LED DRVR WHT BCKLGT 9USMDLM3508TLDKR-ND - IC LED DRVR WHT BCKLGT 9MICROSMDLM3508TLCT-ND - IC LED DRVR WHT BCKLGT 9MICROSMDLM3508TLTR-ND - IC LED DRVR WHT BCKLGT 9MICROSMD |
| LM3423MHX | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM3423MHX/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 |
| LM3423Q0 | 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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