參數(shù)資料
型號(hào)： LM3405A
廠商： National Semiconductor Corporation
英文描述： 1.6MHz, 1A Constant Current Buck LED Driver with Internal Compensation in Tiny SOT23 Package
中文描述： 1.6MHz的，第1A恒流降壓型LED在微型SOT23封裝和內(nèi)部補(bǔ)償驅(qū)動(dòng)器
文件頁(yè)數(shù)： 6/20頁(yè)
文件大?。?/td> 396K
代理商： LM3405A
Block Diagram
30015252
FIGURE 1. Simplified Block Diagram
Application Information
THEORY OF OPERATION
The LM3405A is a PWM, current-mode control switching buck
regulator designed to provide a simple, high efficiency solu-
tion for driving LEDs with a preset switching frequency of
1.6MHz. This high frequency allows the LM3405A to operate
with small surface mount capacitors and inductors, resulting
in LED drivers that need only a minimum amount of board
space. The LM3405A is internally compensated, simple to
use, and requires few external components.
The following description of operation of the LM3405A will re-
fer to the Simplified Block Diagram (
Figure 1
) and to the
waveforms in
Figure 2
. The LM3405A supplies a regulated
output current by switching the internal NMOS power switch
at constant frequency and variable duty cycle. A switching
cycle begins at the falling edge of the reset pulse generated
by the internal oscillator. When this pulse goes low, the output
control logic turns on the internal NMOS power switch. During
this on-time, the SW pin voltage (V
SW
) swings up to approxi-
mately V
, and the inductor current (I
) increases with a linear
slope. I
is measured by the current sense amplifier, which
generates an output proportional to the switch current. The
sense signal is summed with the regulator’s corrective ramp
and compared to the error amplifier’s output, which is propor-
tional to the difference between the feedback voltage and
V
. When the PWM comparator output goes high, the in-
ternal power switch turns off until the next switching cycle
begins. During the switch off-time, inductor current dis-
charges through the catch diode D1, which forces the SW pin
to swing below ground by the forward voltage (V
) of the
catch diode. The regulator loop adjusts the duty cycle (D) to
maintain a constant output current (I
F
) through the LED, by
forcing FB pin voltage to be equal to V
REF
(0.205V).
30015207
FIGURE 2. SW Pin Voltage and Inductor Current
Waveforms of LM3405A
BOOST FUNCTION
Capacitor C3 and diode D2 in
Figure 1
are used to generate
a voltage V
. The voltage across C3, V
- V
, is
the gate drive voltage to the internal NMOS power switch. To
properly drive the internal NMOS switch during its on-time,
V
needs to be at least 2.5V greater than V
. Large
value of V
- V
is recommended to achieve better ef-
ficiency by minimizing both the internal switch ON resistance
(R
DS(ON)
), and the switch rise and fall times. However,
V
- V
SW
should not exceed the maximum operating limit
of 5.5V.
www.national.com
6
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參數(shù)描述
LM3405A_08 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:1.6MHz, 1A Constant Current Buck LED Driver with Internal Compensation in Tiny SOT23 and eMSOP Package
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LM3405AEVAL/NOPB 功能描述:LED 照明開(kāi)發(fā)工具 LM3405A EVAL BOARD RoHS:否 制造商:Fairchild Semiconductor 產(chǎn)品:Evaluation Kits 用于:FL7732 核心: 電源電壓:120V 系列: 封裝:
LM3405AXMK 制造商:NSC 制造商全稱(chēng):National Semiconductor 功能描述:1.6MHz, 1A Constant Current Buck LED Driver with Internal Compensation in Tiny SOT23 and eMSOP Package
LM3405AXMK/NOPB 功能描述:LED照明驅(qū)動(dòng)器 RoHS:否 制造商:STMicroelectronics 輸入電壓:11.5 V to 23 V 工作頻率: 最大電源電流:1.7 mA 輸出電流: 最大工作溫度: 安裝風(fēng)格:SMD/SMT 封裝 / 箱體:SO-16N
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