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參數(shù)資料
| 型號(hào)： | LM3401MM |
| 廠商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分類： | 顯示驅(qū)動(dòng)器 |
| 英文描述： | ProcessorPM Development Kit |
| 中文描述： | LED DISPLAY DRIVER, PDSO8 |
| 封裝： | PLASTIC, MSOP-8 |
| 文件頁數(shù)： | 13/18頁 |
| 文件大?。?/td> | 324K |
| 代理商： | LM3401MM |
Design Example
30021441
FIGURE 11. Example Circuit
The following design example is intended to illustrate the
step-by-step design process described in the previous sec-
tions. The example refers to the circuit in
Figure 11
, and the
results are summaized in
Table 1
. The resulting circuit will
drive a string of 2 Luxeon V Star LEDs at 700 mA from an
input voltage between 18V and 35V.
The example LEDs have a maximum DC current rating of 700
mA, a forward voltage of 5.4V to 8.3V, and a maximum peak
current rating of 1.0A.
First, set the LED DC current with R1:
And the required wattage is:
W
RSNS
= 700 mA
2
x 0.286 = 140 mW
Select a standard value of 290 m
, 1/4W resistor, which will
result in a 690 mA LED DC current.
To keep the peak LED current below I
LED_MAX
, the maximum
hysteresis is determined by:
SNS
HYS_MAX
= (1.0A - .690A) x 0.29
= 90 mV
Which gives a maximum R2 value of:
Next, a preferred switching frequency of 1 MHz is selected for
this example.
Since this is a relatively high switching frequency, a low start-
ing point of 25 mV is selected for the comparator hysteresis
to maintain good line regulation. This will allow a larger in-
ductor at the same operating frequency and is well below the
calculated maximum. Set a preliminary hysteresis value with
R2:
For 1 MHz switching frequency and 25 mV hysteresis, induc-
tance can be calculated. Because frequency varies with input
voltage and LED forward voltage, for this calculation, assume
typical values of 24V and 13.6V respectively, and a PFET
delay time of 15 ns.
Select a value of 33 μH and the hysteresis can be adjusted
downward by re-arranging the same frequency equation:
This gives a new R2 value of 5.6k. This will result in a typical
operating frequency of 1 MHz at 24V
IN
. Next, it must be ver-
ified that the peak LED current is within the maximum allowed.
For now, the design is created without using a ripple reduction
capacitor. Therefore, LED ripple current is equal to inductor
ripple current. Maximum LED ripple current is calculated as:
Note that the maximum input voltage and minimum anode
voltage were used for this worst case calculation.
Now peak LED current can be determined:
13
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| LM3401MM/NOPB | 功能描述:LED照明驅(qū)動(dòng)器 HYSTERETIC PFET CONTROLLER RoHS:否 制造商:STMicroelectronics 輸入電壓:11.5 V to 23 V 工作頻率: 最大電源電流:1.7 mA 輸出電流: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SO-16N |
| LM3401MMX | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:Hysteretic PFET Controller for High Power LED Drive |
| LM3401MMX/NOPB | 功能描述:LED照明驅(qū)動(dòng)器 RoHS:否 制造商:STMicroelectronics 輸入電壓:11.5 V to 23 V 工作頻率: 最大電源電流:1.7 mA 輸出電流: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SO-16N |
| LM3401MMX/S7002590 | 制造商:Rochester Electronics LLC 功能描述: 制造商:Texas Instruments 功能描述: |
| LM3401-MR16DEMO/NOPB | 功能描述:LED 照明開發(fā)工具 LM3401-MR16DEMO RoHS:否 制造商:Fairchild Semiconductor 產(chǎn)品:Evaluation Kits 用于:FL7732 核心: 電源電壓:120V 系列: 封裝: |
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