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| 型号： | LM3423MHBSTEVAL/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 15/67页 |
| 文件大小： | 0K |
| 描述： | BOARD EVAL BOOST FOR 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： | LM3423MHBSTEVAL |
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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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| 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 |
| LM3423Q0MH | 制造商:NSC 制造商全称:National Semiconductor 功能描述:N-Channel Controllers for Constant Current LED Drivers |
| LM3423Q0MH/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 |
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