MAX8790 データシートの表示（PDF） - Maxim Integrated

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MAX8790

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

Maxim Integrated 

MAX8790

EVALUATION KIT AVAILABLE

Six-String White LED Driver with Active

Current Balancing for LCD Panel Applications

General Description

The MAX8790 is a high-efficiency driver for white light-

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

crystal 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 bright-

ness for all LEDs. The MAX8790 has a wide input voltage

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

adjustable 15mA to 25mA full-scale LED current.

The MAX8790 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

signal 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 MAX8790 has multiple features to protect the control-

ler 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 provide

consistent operation and soft-start capability. A thermal-

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 MAX8790 features selectable switching frequen-

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

between external component size and operating efficiency.

The MAX8790 is available in a thermally enhanced,

lead(Pb)-free, 20-pin, 4mm x 4mm, TQFN package.

Applications

●● Notebook, Subnotebook, and Tablet Computer Displays

●● Handy Terminals

Ordering Information

PART

TEMP RANGE

MAX8790ETP+ -40°C to +85°C

PIN-PACKAGE

20 Thin QFN

(4mm x 4mm)

PKG

CODE

T2044-3

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

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

25mA, 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 TQFN Package

Simplified Operating Circuit

VIN

CIN

0.1µF

L1

D1 VOUT

SHDN IN EXT

VCC

FSET

CS

ISET

MAX8790

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.

19-0658; Rev 1; 5/14

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