BOOT

VCC

VIN

SW

CS

DIM

RON

GND

VIN

SENSE

7V BIAS

REGULATOR

BYPASS

SWITCH

VCC

UVLO

THERMAL

SHUTDOWN

ON TIMER

Complete

Start

+

-

300 ns MIN

OFF TIMER

Complete

Start

LOGIC

+

-

+

-

+

-

CURRENT

LIMIT OFF

TIMER

BUCK

SWITCH

CURRENT

SENSE

LEVEL

SHIFT

GATE DRIVE

UVLO

VIN

+

-

0.735A

0.7V

0.2V

0.3V

1.5V

5V

75 PA

SD

LM3402, LM3402HV

SNVS450F – SEPTEMBER 2006 – REVISED OCTOBER 2015

www.ti.com

7 Detailed Description

7.1 Overview

The LM3402 and LM3402HV are buck regulators with a wide input voltage range, low voltage reference, and a

fast output enable/disable function. These features combine to make them ideal for use as a constant current

source for LEDs with forward currents as high as 500 mA. The controlled ON-time (COT) architecture is a

combination of hysteretic mode control and a one-shot ON-timer that varies inversely with input voltage.

Hysteretic operation eliminates the need for small-signal control loop compensation. When the converter runs in

continuous conduction mode (CCM) the controlled ON-time maintains a constant switching frequency over the

range of input voltage. Fast transient response, PWM dimming, a low power shutdown mode, and simple output

overvoltage protection round out the functions of the LM3402/HV.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Controlled ON-time Overview

Figure 17 shows the feedback system used to control the current through an array of LEDs. A voltage signal,

(1)

10

Submit Documentation Feedback

Copyright © 2006–2015, Texas Instruments Incorporated

Product Folder Links: LM3402 LM3402HV