LM3421 datasheet(11/72 Pages) TI1

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AGND

PWM

Start new on time

nDIM

COMP

REFERENCE

CURRENT

LIMIT

CSH

HSN

LOGIC

HSP

OVP

HYSTERESIS

LED CURRENT LOW

UVLO

DDRV

GATE

PGND

OVP

LRDY

RPD

LatchOff

TIMR

OVLO

FLT

LED CURRENT HIGH

Regulator

Thermal

Limit

TLIM

OVLO

PGND

LatchOff

Standby

Dimming

Reset

Dominant

RCT

800 mV

820k

500k

LEB

In the LM3421, TIMR is internally shorted to AGND.

1.235V

6.9V LDO

(4.1V)

DPOL

Grey pins are available in the LM 3423 only.

LEB

9 = 150 ns

VIN/25

VIN UVLO

HYSTERESIS

1.24V

VCC

1.235V

VCC

1.24V

0.245V

1.0V

1.6V

VCC UVLO

VCC

VCC UVLO

VIN

23 2A

11.5 2A

LM3421, LM3421-Q1, LM3423, LM3423-Q1

www.ti.com

SNVS574F – JULY 2008 – REVISED JULY 2015

7 Detailed Description

7.1 Overview

The LM34xx-Q1 are N-channel MOSFET (NFET) controllers for buck, boost and buck-boost current regulators

which are ideal for driving LED loads. The controller has wide input voltage range allowing for regulation of a

variety of LED loads. The high-side differential current sense, with low adjustable threshold voltage, provides an

excellent method for regulating output current while maintaining high system efficiency. The LM34xx-Q1 uses a

Predictive Off-time (PRO) control architecture that allows the regulator to be operated using minimal external

control loop compensation, while providing an inherent cycle-by-cycle current limit. The adjustable current sense

threshold provides the capability to amplitude (analog) dim the LED current and the output enable/disable

function with external dimming FET driver allows for fast PWM dimming of the LED load. When designing, the

maximum attainable LED current is not internally limited because the LM34xx-Q1 is a controller. Instead it is a

function of the system operating point, component choices, and switching frequency allowing the LM34xx-Q1 to

easily provide constant currents up to 5A. This controller contains all the features necessary to implement a high-

efficiency versatile LED driver.

7.2 Functional Block Diagram

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Product Folder Links: LM3421 LM3421-Q1 LM3423 LM3423-Q1

LM3421 Datasheet(PDF) 11 Page - Texas Instruments

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