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| 型号： | LM3421Q1MHX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 15/67页 |
| 文件大小： | 0K |
| 描述： | IC LED DRVR HP CONS CURR 16TSSOP |
| 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： | LM3421Q1MHX |
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SNVS574E – JULY 2008 – REVISED MAY 2013
Method 2 provides a complete dimming range and better noise performance, though it is more complex. It
consists of a PNP current mirror and a bias network consisting of an NPN, 2 resistors and a potentiometer
(R ADJ ), where R ADJ controls the amount of current sourced into the CSH pin. A higher resistance value will source
more current into the CSH pin causing less regulated signal current through R HSP , effectively dimming the LEDs.
V REF should be a precise external voltage reference, while Q7 and Q8 should be a dual pair PNP for best
matching and performance. The additional current (I ADD ) sourced into the CSH pin can be calculated:
§ R ADJ x V REF ·
¨ R
I ADD =
? - V BE-Q6
? ADJ + R MAX 1
R BIAS
(12)
The corresponding I LED for a specific I ADD is:
§ R HSP ·
I LED = (I CSH - I ADD ) x ¨ ?
? R SNS 1
(13)
CURRENT SENSE/CURRENT LIMIT
The LM3421/23 achieves peak current mode control using a comparator that monitors the main MosFET (Q1)
transistor current, comparing it with the COMP pin voltage as shown in Figure 20 . Further, it incorporates a
cycle-by-cycle over-current protection function. Current limit is accomplished by a redundant internal current
sense comparator. If the voltage at the current sense comparator input (IS) exceeds 245 mV (typical), the on
cycle is immediately terminated. The IS input pin has an internal N-channel MosFET which pulls it down at the
conclusion of every cycle. The discharge device remains on an additional 210 ns (typical) after the beginning of a
new cycle to blank the leading edge spike on the current sense signal. The leading edge blanking (LEB)
determines the minimum achievable on-time (t ON-MIN ).
R DS-ON
Sensing
LM3421/23
I T
Q1
R LIM
Sensing
R LIM
GATE
IS
0.8V
COMP
0.245V
PWM
LEB
PGND
Figure 20. Current Sense / Current Limit Circuitry
There are two possible methods to sense the transistor current. The R DS-ON of the main power MosFET can be
used as the current sense resistance because the IS pin was designed to withstand the high voltages present on
the drain when the MosFET is in the off state. Alternatively, a sense resistor located in the source of the MosFET
may be used for current sensing, however a low inductance (ESL) type is suggested. The cycle-by-cycle current
limit (I LIM ) can be calculated using either method as the limiting resistance (R LIM ):
I LIM =
245 mV
R LIM
(14)
Copyright ? 2008–2013, Texas Instruments Incorporated
15
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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|---|---|
| LM3421-SEPICEV/NOPB | 功能描述:电源管理IC开发工具 LM3421-SEPIC EVAL BOARD RoHS:否 制造商:Maxim Integrated 产品:Evaluation Kits 类型:Battery Management 工具用于评估:MAX17710GB 输入电压: 输出电压:1.8 V |
| LM3423 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:N-Channel Controllers for Constant Current LED Drivers |
| LM3423_11 | 制造商:NSC 制造商全称:National Semiconductor 功能描述:LM3423 Buck-Boost 2 Layer Evaluation Board evaluation board showcases most features |
| LM3423BBLSCSEV/NOPB | 功能描述:LED 照明开发工具 LM3423BBLSCS EVAL BOARD RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装: |
| LM3423BS2LYEV/NOPB | 功能描述:LED 照明开发工具 LM3423BS2LY EVAL BOARD RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装: |
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