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General Description

The MAX1698 and MAX1698A are efficient drivers for

white or color LEDs. They are ideal for large LED backlit

displays in PDAs and laptop computers. Numerous

benefits include greater simplicity, lower cost, higher

efficiency, longer bulb life, and greater reliability when

compared to fluorescent (CCFL) and electrolumines-

cent (EL) lamps.

The MAX1698/MAX1698A are switch-mode boost con-

trollers in which LED current, rather than output voltage,

is regulated The devices drive series-connected LEDs

with a controlled current that is measured with a typical-

ly 15Ω sense resistor, not an expensive fractional-ohm

value. LED current control and dimming are accom-

plished with an adjust input (ADJ). For larger light out-

put, multiple LED banks can be connected in parallel

with up to 5W total output power.

The MAX1698A has a higher, and more accurately

specified, CS current limit than the MAX1698 for higher-

power applications of 5W or more. Both devices are

supplied in a space-saving 10-pin µMAX package that

occupies half the space of an 8-pin SO. An evaluation

kit (MAX1698EVKIT) is available to speed designs.

Applications

Battery-Powered Backlight Applications

Backlight for LCD Panels

Notebook PCs

Handy Terminals

PDAs

Features

♦ Over 90% Efficiency

♦ Lossless, Adjustable LED Brightness

♦ Space-Saving 10-Pin µMAX Package

♦ Simpler, Lower Cost, More Reliable Compared

to CCFL or EL Backlights

♦ Up to 5W Output Power

MAX1698/MAX1698A

High-Efficiency Step-Up

Current Regulator for LEDs

________________________________________________________________ Maxim Integrated Products 1

EXT

PGND

GNDADJ

REF

MAX1698

MAX1698A

µMAX

TOP VIEW

FBGND

SHDN

OUT

SHDN

GND

ADJ

REF

OFF

PGND

EXT

BATT

LED

MAX1698

MAX1698A

Typical Operating Circuit

19-1621; Rev 2; 2/07

Pin Configuration

Ordering Information

PART T EM P RA N G E

PIN -

PA C K A G E

PKG

CODE

MAX1698EUB -40°C to +85°C

10µMAX

U10-2

MAX1698AEUB -40°C to +85°C

10µMAX

U10-2

Summary of content (8 pages)

PAGE 1
9-1621; Rev 2; 2/07 High-Efficiency Step-Up Current Regulator for LEDs Features The MAX1698 and MAX1698A are efficient drivers for white or color LEDs. They are ideal for large LED backlit displays in PDAs and laptop computers. Numerous benefits include greater simplicity, lower cost, higher efficiency, longer bulb life, and greater reliability when compared to fluorescent (CCFL) and electroluminescent (EL) lamps.
PAGE 2
MAX1698/MAX1698A High-Efficiency Step-Up Current Regulator for LEDs ABSOLUTE MAXIMUM RATINGS VCC, SHDN to GND ..................................................-0.3V to +6V EXT, FB, CS, ADJ, REF to GND..................-0.3V to (VCC + 0.3V) GND to PGND.....................................................................±0.3V Continuous Power Dissipation (TA = +70°C) 10-Pin µMAX (derate 5.6mW/°C above +70°C) ............444mW Operating Temperature Range ...........................
PAGE 3
High-Efficiency Step-Up Current Regulator for LEDs MAX1698/MAX1698A ELECTRICAL CHARACTERISTICS (VCC = +3.3V, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL Supply Voltage VCC Quiescent Supply Current ICC Undervoltage Lockout FB Regulation Voltage VFB CS Trip Current CONDITIONS MIN 2.7 VFB = 0.3V MAX UNITS 5.5 V 500 µA V Rising edge 2.20 2.65 ADJ = REF 280 320 VADJ = 100mV 13 35 MAX1698A 2.0 3.0 MAX1698 0.8 3.0 0.6 1.
PAGE 4
Typical Operating Characteristics (Circuit of Figure 2, VCC = VBATT = 3.3V, VADJ = VREF, TA = +25°C, unless otherwise noted.) NORMALIZED OUTPUT CURRENT vs. ADJ VOLTAGE vs. VCC 15 10 5 22.0 1.0 OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) 20 1.2 MXA1698-02 vs. VBATT NORMALIZED OUTPUT CURRENT MXA1698-01 25 OUTPUT CURRENT vs. INPUT VOLTAGE 0.8 0.6 0.4 MXA1698-03 OUTPUT CURRENT vs. VBATT AND VCC 21.5 21.0 20.5 0.2 1 CHAIN OF 4 LEDs 1 CHAIN OF 4 LEDs 0 0 2 3 4 5 6 7 8 9 10 0 0.
PAGE 5
High-Efficiency Step-Up Current Regulator for LEDs PIN NAME FUNCTION 1 VCC 2 SHDN 3 REF 1.25V Reference Output. Capable of sourcing 150µA for external loads. This pin is internally compensated. Do not connect any bypass capacitors at REF. 4 ADJ Adjust Input. Allows dynamic adjustment of the output current. FB regulates to 300mV when ADJ = REF. 5, 7 GND Ground 6 FB 8 PGND 9 CS FET Current-Sense Input 10 EXT Gate Driver Output IC Supply Voltage Input. Power for internal circuitry.
PAGE 6
MAX1698/MAX1698A High-Efficiency Step-Up Current Regulator for LEDs 10µH VBATT = 3.3V MBR0540 10µF 1µF VCC = 3.3V EXT VCC 1µF MAX1698 MAX1698A SHDN CS REF LEDs OPTIONAL DZ ADJ FB GND PGND RFB 15Ω 15Ω 15Ω 15Ω Figure 2. Typical Operating Circuit Detailed Description The MAX1698/MAX1698As' high efficiency and small size make them ideally suited to drive LEDs. They operate as a boost DC-DC converter that controls output current rather than voltage.
PAGE 7
High-Efficiency Step-Up Current Regulator for LEDs REF MAX1698 MAX1698A 500k ADJ GND Catch Diode (D1) Selection Figure 3. Adjusting LED Current shows the standard method of setting the ADJ voltage. Use the following equation to determine ILED: VADJ I LED = 4.16 ⋅ RFB where VADJ is the voltage at ADJ. Note that ADJ voltages below 50mV turn the LEDs off. Inductor Selection Choose an inductor with low DC resistance (in the neighborhood of 100mΩ) to minimize losses.
PAGE 8
Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information go to www.maxim-ic.com/packages.) e 10LUMAX.EPS MAX1698/MAX1698A High-Efficiency Step-Up Current Regulator for LEDs 4X S 10 10 INCHES H Ø0.50±0.1 0.6±0.1 1 1 0.6±0.1 BOTTOM VIEW TOP VIEW D2 MILLIMETERS MAX DIM MIN 0.043 A 0.006 A1 0.002 A2 0.030 0.037 0.120 D1 0.116 0.118 0.114 D2 0.116 0.120 E1 0.118 E2 0.114 0.199 H 0.187 L 0.0157 0.