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| 型号： | LM3421MHX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 16/67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
OVER-CURRENT PROTECTION
The LM3421/23 devices have a secondary method of over-current protection. Switching action is disabled
whenever the current in the LEDs is more than 30% above the regulation set point. The dimming MosFET switch
driver (DDRV) is not disabled however as this would immediately remove the fault condition and cause oscillatory
behavior.
ZERO CURRENT SHUTDOWN
The LM3421/23 devices implement "zero current" shutdown via the EN and RPD pins. When pulled low, the EN
pin places the devices into near-zero current state, where only the leakage currents will be observed at the pins
(typical 0.1 μA). The applications circuits, frequently have resistor dividers to set UVLO, OVLO, or other similar
functions. The RPD pin is an open drain N-channel MosFET that is enabled only when the device is enabled.
Tying the bottom of all resistor dividers to the RPD pin as shown in Figure 21 allows them to float during
shutdown, thus removing their current paths and providing true application-wide zero current shutdown.
V IN
L1
D1
V O
Enable
LM3421/23
R UV2
EN
V IN
nDIM
OVP
RPD
R OV2
R OV1
R UV1
Figure 21. Zero Current Shutdown Circuit
CONTROL LOOP COMPENSATION
The LM3421/23 control loop is modeled like any current mode controller. Using a first order approximation, the
uncompensated loop can be modeled as a single pole created by the output capacitor and, in the boost and
buck-boost topologies, a right half plane zero created by the inductor, where both have a dependence on the
LED string dynamic resistance. There is also a high frequency pole in the model, however it is near the switching
frequency and plays no part in the compensation design process therefore it will be neglected. Since ceramic
capacitance is recommended for use with LED drivers due to long lifetimes and high ripple current rating, the
ESR of the output capacitor can also be neglected in the loop analysis. Finally, there is a DC gain of the
uncompensated loop which is dependent on internal controller gains and the external sensing network.
A buck-boost regulator will be used as an example case. See the Design Guide section for compensation of all
topologies.
The uncompensated loop gain for a buck-boost regulator is given by the following equation:
¨ 1 -
¨ 1 +
s ·
Z Z 1 ?
s ·
Z P 1 ?
T U = T U 0 x
§
¨
?
§
¨
?
?
1
?
1
(15)
Where the uncompensated DC loop gain of the system is described as:
T U 0 =
D c x 500V x R CSH x R SNS
( 1 + D ) x R HSP x R LIM
=
D c x 620V
( 1 + D ) x I LED x R LIM
(16)
3
Z P 1 =
And the output pole ( ω P1 ) is approximated:
1+ D
r D x C O
(17)
16
Copyright ? 2008–2013, Texas Instruments Incorporated
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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