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| 型号： | LM3421Q1MHX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 17/67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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And the right half plane zero ( ω Z1 ) is:
SNVS574E – JULY 2008 – REVISED MAY 2013
Z Z 1 =
r D x D c 2
D x L1
(18)
100
80
? Z1
? P1
135
90
GAIN
60
40
20
0
-20
-40
-60
PHASE
0° Phase Margin
45
0
-45
-90
-135
-180
-225
1e-1
1e1
1e3
1e5
1e7
FREQUENCY (Hz)
Figure 22. Uncompensated Loop Gain Frequency Response
Figure 22 shows the uncompensated loop gain in a worst-case scenario when the RHP zero is below the output
pole. This occurs at high duty cycles when the regulator is trying to boost the output voltage significantly. The
RHP zero adds 20dB/decade of gain while loosing 45°/decade of phase which places the crossover frequency
(when the gain is zero dB) extremely high because the gain only starts falling again due to the high frequency
pole (not modeled or shown in figure). The phase will be below -180° at the crossover frequency which means
there is no phase margin (180° + phase at crossover frequency) causing system instability. Even if the output
pole is below the RHP zero, the phase will still reach -180° before the crossover frequency in most cases yielding
instability.
LM3421/23
I LED
R HSP
HSP
High-Side
Sense Amplifier
C FS
V SNS
R SNS
R HSN
HSN
R FS
sets ? P3
sets ? P2
R CSH
C CMP
CSH
COMP
1.24V
Error Amplifier
To PWM
Comparator
R O
Figure 23. Compensation Circuitry
To mitigate this problem, a compensator should be designed to give adequate phase margin (above 45°) at the
crossover frequency. A simple compensator using a single capacitor at the COMP pin (C CMP ) will add a dominant
pole to the system, which will ensure adequate phase margin if placed low enough. At high duty cycles (as
shown in Figure 22 ), the RHP zero places extreme limits on the achievable bandwidth with this type of
compensation. However, because an LED driver is essentially free of output transients (except catastrophic
failures open or short), the dominant pole approach, even with reduced bandwidth, is usually the best approach.
The dominant compensation pole ( ω P2 ) is determined by C CMP and the output resistance (R O ) of the error
amplifier (typically 5 M ? ):
Copyright ? 2008–2013, Texas Instruments Incorporated
17
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 |
|---|---|
| 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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