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| 型号： | LM3421MHX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 19/67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
START-UP REGULATOR
The LM3421/23 includes a high voltage, low dropout bias regulator. When power is applied, the regulator is
enabled and sources current into an external capacitor (C BYP ) connected to the V CC pin. The recommended
bypass capacitance for the V CC regulator is 2.2 μF to 3.3 μF. The output of the V CC regulator is monitored by an
internal UVLO circuit that protects the device from attempting to operate with insufficient supply voltage and the
supply is also internally current limited. Figure 25 shows the typical start-up waveforms for the LM3421/23.
First, C BYP is charged to be above V CC UVLO threshold (~4.2V). The C VCC charging time (t VCC ) can be estimated
as:
t VCC =
4 . 2 V
25 mA
x C BYP = 168 : x C BYP
(22)
C CMP is then charged to 0.9V over the charging time (t CMP ) which can be estimated as:
t CMP =
0.9V
25 P A
x C CMP = 36 k : x C CMP
(23)
Once C CMP = 0.9V, the part starts switching to charge C O until the LED current is in regulation. The C O charging
time (t CO ) can be roughly estimated as:
t CO = C O x
V O
I LED
(24)
The system start-up time (t SU ) is defined as:
t SU = t VCC + t CMP + t CO
(25)
In some configurations, the start-up waveform will overshoot the steady state COMP pin voltage. In this case, the
LED current and output voltage will overshoot also, which can trip the over-voltage or protection, causing a race
condition. The easiest way to prevent this is to use a larger compensation capacitor (C CMP ), thereby slowing
down the control loop.
OVER-VOLTAGE LOCKOUT (OVLO)
V O
LM3421/23
23 P A
R OV2
OVP
1.24V
OVLO
R OV1
Figure 26. Over-Voltage Protection Circuitry
The LM3421/23 can be configured to detect an output (or input) over-voltage condition via the OVP pin. The pin
features a precision 1.24V threshold with 23 μA (typical) of hysteresis current as shown in Figure 26 . When the
OVLO threshold is exceeded, the GATE pin is immediately pulled low and a 23 μA current source provides
hysteresis to the lower threshold of the OVLO hysteretic band.
If the LEDs are referenced to a potential other than ground (floating), as in the buck-boost and buck
configuration, the output voltage (V O ) should be sensed and translated to ground by using a single PNP as
The over-voltage turn-off threshold (V TURN-OFF ) is defined:
Ground Referenced
V TURN - OFF = 1 . 24V x ¨ ¨ OV 1
§ R + R OV 2 ·
?
? R OV 1 1
?
(26)
Copyright ? 2008–2013, Texas Instruments Incorporated
19
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 |
|---|---|
| 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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