Datasheet > LM3405_08

LM3405_08

更新时间： 2024-09-27 11:34:55

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Powering and Dimming High-Brightness LEDs with the LM3405 Constant-Current Buck Regulator

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LM3405_08 数据手册

National Semiconductor

Application Note 1644

Vinit Jayaraj

Powering and Dimming

High-Brightness LEDs with

the LM3405 Constant-

Current Buck Regulator

January 17, 2008

The LM3405 is a 1A, constant-current buck regulator de-

signed to provide a simple, highly-efficient solution for pow-

ering LEDs with the highest power density. The low-feedback

reference voltage of 205 mV (typical) allows the use of LEDs

with large forward voltages. The LM3405 LED driver comes

with an integrated 1A high-side power switch, internal current

limit, over-voltage protection and thermal shutdown. The

LM3405 driver utilizes current mode control with internal com-

pensation offering ease-of-use and predictable, high-perfor-

mance regulation over a wide range of operating conditions.

This article describes a few of the many application solutions

for the LM3405 LED driver. The LM3405 device is offered in

a 6-pin Thin-SOT (TSOT) package and operates at an internal

switching frequency of 1.6 MHz, allowing the use of small-

value inductors, thereby saving board space.

Typical Application Circuit

Figure 1 shows the typical application circuit using the

LM3405 regulator driving a single LED. The boost voltage can

be derived from V_INor V_OUT. The BOOST to SW voltage

(VBOOST-VSW) should never exceed the operating limit of

5.5V, and must be greater than 2.5V for optimum efficiency.

30022901

FIGURE 1. Typical Application Circuit

In the above circuit, the maximum V_INis 5V and therefore the

boost voltage is derived from V_IN. The LM3405 data sheet

provides a detailed description of various circuits for boost-

voltage generation. The LM3405 driver tightly regulates the

FB-pin voltage to 205 mV (typical) and this allows the LED

current (I_F) to be set by the following equation:

off the internal power switch on a cycle-by-cycle basis. In case

of an over voltage (sensed at the FB pin), the internal power

switch is turned off. The LM3405 regulator also has a built-in

thermal shutdown (with hysteresis) which also turns off the

internal power switch if the die temperature exceeds a typical

value of 165°C.

PWM Dimming Using the EN/DIM Pin

The LEDs can be dimmed by applying a PWM-logic signal to

the EN/DIM pin of the LM3405 driver as shown in Figure 2.

R1 (min) is 200 mΩ such that I_F(max) is limited to 1A. In case

of an over current, the internal current limit will trigger and turn

300229

www.national.com

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LM34058ABRG	LIGHTKEY	获取价格	3.40 inch 5x8 Dual Color Dot Matrix LED Display
LM34058ARG	LIGHTKEY	获取价格	3.40 inch 5x8 Dual Color Dot Matrix LED Display
LM34058AURUG	LIGHTKEY	获取价格	3.40 inch 5x8 Dual Color Dot Matrix LED Display
LM34058BRG	LIGHTKEY	获取价格	3.40 inch 5x8 Dual Color Dot Matrix LED Display
LM34058BURUG	LIGHTKEY	获取价格	3.40 inch 5x8 Dual Color Dot Matrix LED Display
LM3405A	NSC	获取价格	1.6MHz, 1A Constant Current Buck LED Driver with Internal Compensation in Tiny SOT23 Packa
LM3405A	TI	获取价格	LM3405A 1.6MHz, 1A Constant Current Buck LED Driver with Internal ensation in Tiny SOT and
LM3405A_08	NSC	获取价格	1.6MHz, 1A Constant Current Buck LED Driver with Internal Compensation in Tiny SOT23 and e
LM3405AXMK	NSC	获取价格	1.6MHz, 1A Constant Current Buck LED Driver with Internal Compensation in Tiny SOT23 Packa
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