- 您现在的位置：买卖IC网 > PDF目录20782 > LM3421MHX/NOPB (National Semiconductor)IC LED DRVR HP CONS CURR 16TSSOP PDF资料下载
参数资料
| 型号： | LM3421MHX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 26/67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 |
第1页第2页第3页第4页第5页第6页第7页第8页第9页第10页第11页第12页第13页第14页第15页第16页第17页第18页第19页第20页第21页第22页第23页第24页第25页当前第26页第27页第28页第29页第30页第31页第32页第33页第34页第35页第36页第37页第38页第39页第40页第41页第42页第43页第44页第45页第46页第47页第48页第49页第50页第51页第52页第53页第54页第55页第56页第57页第58页第59页第60页第61页第62页第63页第64页第65页第66页第67页
SNVS574E – JULY 2008 – REVISED MAY 2013
The chosen input capacitors must also have the necessary RMS current rating. Ceramic capacitors are again the
best choice due to their high ripple current rating, long lifetime, and good temperature performance. An X7R
dieletric rating is suggested.
For most applications, it is recommended to bypass the V IN pin with an 0.1 μF ceramic capacitor placed as close
as possible to the pin. In situations where the bulk input capacitance may be far from the LM3421/23 device, a
10 ? series resistor can be placed between the bulk input capacitance and the bypass capacitor, creating a
150 kHz filter to eliminate undesired high frequency noise.
MAIN MosFET / DIMMING MosFET
The LM3421/23 requires an external NFET (Q1) as the main power MosFET for the switching regulator. Q1 is
recommended to have a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe
operation during the ringing of the switch node. In practice, all switching regulators have some ringing at the
switch node due to the diode parasitic capacitance and the lead inductance. The current rating is recommended
to be at least 10% higher than the average transistor current. The power rating is then verified by calculating the
power loss given the RMS transistor current and the NFET on-resistance (R DS-ON ).
When PWM dimming, the LM3421/23 requires another MosFET (Q2) placed in series (or parallel for a buck
regulator) with the LED load. This MosFET should have a voltage rating equal to the output voltage (V O ) and a
current rating at least 10% higher than the nominal LED current (I LED ) . The power rating is simply V O multiplied
by I LED , assuming 100% dimming duty cycle (continuous operation) will occur.
In general, the NFETs should be chosen to minimize total gate charge (Q g ) when f SW is high and minimize R DS-ON
otherwise. This will minimize the dominant power losses in the system. Frequently, higher current NFETs in
larger packages are chosen for better thermal performance.
RE-CIRCULATING DIODE
A re-circulating diode (D1) is required to carry the inductor current during t OFF . The most efficient choice for D1 is
a Schottky diode due to low forward voltage drop and near-zero reverse recovery time. Similar to Q1, D1 is
recommended to have a voltage rating at least 15% higher than the maximum transistor voltage to ensure safe
operation during the ringing of the switch node and a current rating at least 10% higher than the average diode
current. The power rating is verified by calculating the power loss through the diode. This is accomplished by
checking the typical diode forward voltage from the I-V curve on the product datasheet and multiplying by the
average diode current. In general, higher current diodes have a lower forward voltage and come in better
performing packages minimizing both power losses and temperature rise.
BOOST INRUSH CURRENT
When configured as a boost converter, there is a “phantom” power path comprised of the inductor, the output
diode, and the output capacitor. This path will cause two things to happen when power is applied. First, there will
be a very large inrush of current to charge the output capacitor. Second, the energy stored in the inductor during
this inrush will end up in the output capacitor, charging it to a higher potential than the input voltage.
Depending on the state of the EN pin, the output capacitor would be discharged by:
1. EN < 1.3V: no discharge path (leakage only).
2. EN > 1.3V, the OVP divider resistor path, if present, and 10μA into each of the HSP & HSN pins.
In applications using the OVP divider and with EN > 1.3V, the output capacitor voltage can charge higher than
V TURN-OFF . In this situation, the FLT pin (LM3423 only) is open and the PWM dimming MosFET is turned off. This
condition (the system appearing disabled) can persist for an undesirably long time. Possible solutions to this
condition are:
?
?
?
?
Add an NTC thermistor in series with the input to prevent the inrush from overcharging the output capacitor
too high.
Use a current limited source supply.
Raise the OVP threshold.
26
Copyright ? 2008–2013, Texas Instruments Incorporated
Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1
相关PDF资料 |
PDF描述 |
|---|---|
| ECC07DRYN | CONN EDGECARD 14POS DIP .100 SLD |
| RS3-4809D | CONV DC/DC 3W 36-72VIN +/-09VOUT |
| GEM10DRSN-S288 | CONN EDGECARD 20POS .156 EXTEND |
| EVW020A0A41-HZ | CONVERTER DC/DC 5.0V 20A OUTPUT |
| RS3-4805D | CONV DC/DC 3W 36-72VIN +/-05VOUT |
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 |
发布紧急采购，3分钟左右您将得到回复。