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參數(shù)資料
| 型號(hào)： | LM3407 |
| 廠商： | National Semiconductor Corporation |
| 英文描述： | 350 mA, Constant Current Output Floating Buck Switching Converter for High Power LEDs |
| 中文描述： | 350毫安，恒流輸出浮點(diǎn)高功率LED的降壓開(kāi)關(guān)轉(zhuǎn)換器 |
| 文件頁(yè)數(shù)： | 10/16頁(yè) |
| 文件大小： | 321K |
| 代理商： | LM3407 |
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FIGURE 4. Implementation of the PWM Switching Signal
30046624
FIGURE 5. Waveforms of V
ISNS
and V
RP
Under Closed Loop Operation
INTERNAL VCC REGULATOR
The LM3407 has an internal 4.5V linear regulator. This regu-
lated voltage is used for powering the internal circuitry only
and any external loading at the VCC pin is not recommended.
The supply input (V
IN
) can be connected directly to an input
voltage up to 30V. The VCC pin provides voltage regulated at
4.5V for V
≤
6V. For 4.5V
≤
V
≤
6V, VIN pin will be con-
nected to VCC pin directly by an internal bypassing switch.
For stability reason, an external capacitor C
with at least
680 nF (1 μF recommended) must be connected to the VCC
pin.
CLOCK GENERATOR
The LM3407 features an integrated clock generator to control
the switching frequency of the converter, f
. An external re-
sistor R
, connected to the FS pin and ground, determines
the switching frequency. The oscillator frequency can be set
in the range of 300 kHz to 1 MHz. The relationship between
the frequency setting resistance and the oscillator frequency
is described in the Application Information Section.
PWM DIMMING OF LED STRING
Dimming of LED brightness is achieved by Pulse Width Mod-
ulation (PWM) control of the LED current. Pulse Width Mod-
ulation control allows LED brightness to be adjusted while still
maintaining accurate LED color temperature. The LM3407
accepts an external PWM dimming signal at the DIM pin. The
signal is buffered before being applied to the internal switch
control block responsible for controlling the ON/OFF of the
power switch, Q1. The DIM pin is internally pulled low by a
resistor and no LED current will be available when the DIM
pin is floating or shorted to ground. Functionally, the DIM pin
can also be used as an external device disable control. Device
switching will be disabled if the DIM pin is not connected or
tied to ground.
LOW POWER SHUTDOWN MODE
The LM3407 comes with a dedicated device enable pin, EN,
for low power shutdown of the device. By putting the device
in shutdown mode, most of the internal circuits will be disabled
and the input current will reduced to below typically 50μA. The
EN pin is internally pulled high by a 5μA current source. Con-
necting the EN pin to ground will force the device to enter low
power shutdown mode. To resume normal operation, leave
the EN pin open or drive with a logic high voltage.
INPUT UNDER-VOLTAGE LOCK-OUT (UVLO)
The LM3407 incorporates an input Under-Voltage Lock-Out
(UVLO) circuit with hysteresis to keep the device disabled
when the input voltage (V
IN
) falls below the Lock-Out Low
threshold, 3.4V typical. During the device power-up, internal
circuits are held inactive and the UVLO comparator monitors
the voltage level at the VIN pin continuously. When the VIN
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| LM3407_09 | 制造商:NSC 制造商全稱:National Semiconductor 功能描述:350 mA, Constant Current Output Floating Buck Switching Converter for High Power LEDs |
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| LM3407MY | 制造商:Texas Instruments 功能描述:Conv DC-DC Single Step Down 4.5V to 30V 8-Pin MSOP EP T/R 制造商:Texas Instruments 功能描述:BUCK SW CONVERTER, 350MA, POWERWISE |
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