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MAX8790A

Six-String White LED Driver with Active Current Balancing for LCD Panel Applications

Maxim Integrated 

MAX8790A

EVALUATION KIT AVAILABLE

Six-String White LED Driver with Active

Current Balancing for LCD Panel Applications

General Description

The MAX8790A is a high-efficiency driver for white light-

emitting diodes (LEDs). It is designed for large liquidcrys-

tal displays (LCDs) that employ an array of LEDs as the

light source. A current-mode step-up controller drives up

to six parallel strings of multiple series-connected LEDs.

Each string is terminated with ballast that achieves ±1.5%

current regulation accuracy, ensuring even brightness for

all LEDs. The MAX8790A has a wide input-voltage range

from 4.5V to 26V, and provides a fixed 20mA or adjustable

15mA to 27mA full-scale LED current.

The MAX8790A has two dimming control modes to enable

a wide variety of applications. In direct DPWM mode, the

LED current is directly turned on and off by a PWM signal.

In analog dimming mode, an internal phase-locked loop

(PLL) circuit translates the PWM signal into an analog sig-

nal and linearly controls the LED current down to 12.5%.

Below 12.5%, digital dimming is added to allow lower

average LED current down to 1%. Both control methods

provide 100:1 dimming range.

The MAX8790A has multiple features to protect the con-

troller from fault conditions. Separate feedback loops limit

the output voltage if one or more LEDs fail open or short.

The controller features cycle-by-cycle current limit to pro-

vide consistent operation and soft-start capability. A ther-

mal-shutdown circuit provides another level of protection.

The step-up controller uses an external MOSFET, which

provides good efficiency and allows for scalable output

power and maximum operating voltage. Low feedback

voltage at each LED string (450mV) helps reduce power

loss. The MAX8790A features selectable switching fre-

quency (500kHz, 750kHz, or 1MHz), which allows trade-offs

between external component size and ope-rating efficiency.

The MAX8790A is available in a thermally enhanced,

lead-free, 20-pin, 4mm x 4mm, thin QFN package.

Applications

●● Notebook, Subnotebook, and Tablet Computer

Displays

●● Handy Terminals

Ordering Information

PART

MAX8790AETP+

TEMP RANGE

-40°C to +85°C

PIN-PACKAGE

20 TQFN-EP*

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

Features

●● Drives Six Parallel Strings with Multiple Series-

Connected LEDs per String

●● ±1.5% Current Regulation Accuracy Between Strings

●● Low 450mV Feedback Voltage at Full Current

Improves Efficiency

●● Step-Up Controller Regulates the Output Just Above

the Highest LED String Voltage

●● Full-Scale LED Current Adjustable from 15mA to

27mA, or Preset 20mA

●● Wide 100:1 Dimming Range

●● Programmable Dimming Control: Direct DPWM or

Analog Dimming

●● Built-In PLL for Synchronized Dimming Control

●● Open and Short LED Protections

●● Output Overvoltage Protection

●● Wide Input Voltage Range from 4.5V to 26V

●● External MOSFET Allows a Large Number of LEDs

per String

●● 500kHz/750kHz/1MHz Switching Frequency

●● Small, 20-Pin, 4mm x 4mm Thin QFN Package

Simplified Operating Circuit

VIN

CIN

0.1µF

L1

D1 VOUT

SHDN IN EXT

VCC

FSET

CS

ISET

MAX8790A

GND

BRT

N.C. OSC

OV

N.C. CPLL

CCV

FB1

FB2

ENA

FB3

FB4

EP

FB5

FB6

N1

RS

R1

R2

Pin Configuration appears at end of data sheet.

19-0989; Rev 1; 10/14

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