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参数资料
| 型号： | LM3421MHX/NOPB |
| 厂商： | National Semiconductor |
| 文件页数： | 20/67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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V TURN - OFF = 1 . 24V x ¨ ¨
R OV 1
SNVS574E – JULY 2008 – REVISED MAY 2013
Floating
?
§ 0 . 5 x R OV1 + R OV2 ·
?
? 1
(27)
In the ground referenced configuration, the voltage across R OV2 is V O - 1.24V whereas in the floating
configuration it is V O - 620 mV where 620 mV approximates V BE of the PNP.
The over-voltage hysteresis (V HYSO ) is defined:
V HYSO = 23 P A x R OV 2
(28)
LED+
R OV2
LM3421/23
LED-
OVP
R OV1
Figure 27. Floating Output OVP Circuitry
The OVLO feature can cause some interesting results if the OVLO trip-point is set too cose to V O . At turn-on, the
converter has a modest amount of voltage overshoot before the control loop gains control of I LED . If the overshoot
exceeds the OVLO threshold, the controller shuts down, opening the dimming MosFET. This isolates the LED
load from the converter and the output capacitance. The voltage will then discharge very slowly through the HSP
and HSN pins until V O drops below the lower threshold, where the process repeats. This looks like the LEDs are
blinking at around 2 Hz. This mode can be escaped if the input voltage is reduced.
INPUT UNDER-VOLTAGE LOCKOUT (UVLO)
The nDIM pin is a dual-function input that features an accurate 1.24V threshold with programmable hysteresis as
shown in Figure 28 . This pin functions as both the PWM dimming input for the LEDs and as a V IN UVLO. When
the pin voltage rises and exceeds the 1.24V threshold, 23 μA (typical) of current is driven out of the nDIM pin into
the resistor divider providing programmable hysteresis.
V IN
LM3421/23
23 P A
R UV2
R UV1
R UVH
(optional)
nDIM
1.24V
UVLO
Figure 28. UVLO Circuit
When using the nDIM pin for UVLO and PWM dimming concurrently, the UVLO circuit can have an extra series
resistor to set the hysteresis. This allows the standard resistor divider to have smaller resistor values minimizing
PWM delays due to a pull-down MosFET at the nDIM pin (see PWM DIMMING section). In general, at least 3V
of hysteresis is preferable when PWM dimming, if operating near the UVLO threshold.
The turn-on threshold (V TURN-ON ) is defined as follows:
20
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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