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General Description

The MAX8901A/MAX8901B step-up converters drive from

two to six series-connected white LEDs (WLEDs) with

constant current to provide uniform WLED intensity for

LCD backlighting in cell phones, PDAs, and other hand-

held devices. The MAX8901_ operate at a fixed 750kHz

(typ) switching frequency, allowing for tiny external com-

ponents, and are optimized for the highest possible effi-

ciency over the full 1-cell Li+/Li-Poly battery range.

These converters use a single input (ON) to enable the

IC and to control WLED intensity. The MAX8901A

requires a direct PWM input to regulate WLED intensity

with the WLED current proportional to the PWM duty

cycle. The MAX8901B uses single-wire, serial-pulse

dimming that reduces the WLED intensity in 32 linear

steps. Full-scale WLED current for serial-pulse

dimming is 24.75mA (MAX8901B, 0.75mA/step).

The MAX8901_ feature an internal soft-start to eliminate

inrush currents during startup, input overvoltage

protection, WLED overvoltage protection, and a shut-

down mode with 0.01µA (typ) shutdown current. No

WLED current is present in shutdown provided the

WLED forward voltage is greater than the input supply

voltage. Additional features include undervoltage lock-

out (UVLO) and thermal shutdown.

The MAX8901_ are available in tiny 8-pin, 2mm x 2mm

TDFN-EP packages (0.8mm max height).

Applications

Display Backlight (from 2 to 6 WLEDs)

Cellular Phones

PDAs and Smartphones

MP3 and Portable Media Players

Portable Navigation Devices

Digital Cameras

Features

o High Efficiency, Up to 91%

o 2.6V to 5.5V Input Voltage Range

o Fixed-Frequency Operation

o Supplies from 2 to 6 WLEDs with 1.3% LED Current

Accuracy

o Flexible Dimming Control

Direct PWM Dimming (MAX8901A)

32-Step, Single-Wire Serial Dimming

(MAX8901B)

o Input Undervoltage Lockout

o Input Overvoltage Lockout

o WLED Overvoltage Protection (25V typ)

o 0.01µA (typ) Shutdown Current

o No WLED Current in Shutdown

o Internal Soft-Start and Thermal Shutdown

MAX8901A/MAX8901B

Highest Efficiency Supply for 2 to 6

Series WLEDs in a 2mm x 2mm TDFN Package

________________________________________________________________

Maxim Integrated Products

Ordering Information

MAX8901A

COMP

GND

OVP

PGND

OUTPUT

UP TO 25V

INPUT

2.6V TO 5.5V

PWM DIMMING

CONTROL

Typical Operating Circuits

19-0865; Rev 3; 8/10

Note: All devices are specified over the -40°C to +85°C operating

temperature range.

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

EP = Exposed pad.

T = Tape and reel.

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim's website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

PART PIN-PACKAGE TOP MARK

MAX8901AETA+T

8 TDFN-EP*

2mm x 2mm

+ABA

MAX8901BETA+T

8 TDFN-EP*

2mm x 2mm

+ABB

MAX8901B

COMP

GND

OVP

PGND

OUTPUT

UP TO 25V

INPUT

2.6V TO 5.5V

SERIAL-PULSE

DIMMING

CONTROL

Pin Configuration appears at end of data sheet.

Summary of content (14 pages)

PAGE 1
9-0865; Rev 3; 8/10 KIT ATION EVALU E L B AVAILA Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package The MAX8901A/MAX8901B step-up converters drive from two to six series-connected white LEDs (WLEDs) with constant current to provide uniform WLED intensity for LCD backlighting in cell phones, PDAs, and other handheld devices.
PAGE 2
MAX8901A/MAX8901B Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package ABSOLUTE MAXIMUM RATINGS IN to GND .................................................................-0.3V to +7V CS, COMP, ON to GND ...............................-0.3V to (VIN + 0.3V) OVP, LX to GND .....................................................-0.3V to +28V PGND to GND .......................................................-0.3V to +0.3V LX Current ......................................................
PAGE 3
Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package (VIN = VON = VOVP = 3.6V, VPGND = VGND = 0V, COMP, CS, and LX are unconnected, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1) PARAMETER SYMBOL Serial Dimming Full-Scale LED Current Accuracy CONDITIONS ILED = 24.75mA (MAX8901B) PWM Frequency for PWM Dimming Control MIN TA = +25°C MAX UNITS -1.3 +1.
PAGE 4
Typical Operating Characteristics (Circuit of Figure 5, ILED = 24.75mA, VIN = VON = 3.6V, C1 = 1µF, C2 = 1µF, TA = +25°C, unless otherwise noted.) LED EFFICIENCY vs. INPUT VOLTAGE 3 WLEDs 4 WLEDs 80 6 WLEDs 85 75 3 WLEDs 80 6 WLEDs 75 INDUCTOR: TOKO 1069AS-220M DIODE: CENTRAL SEMI CMDSH05-4 INDUCTOR: TOKO 1098AS-100M DIODE: NXP PMEG3005EB 70 70 3 4 5 6 3 4 5 6 INPUT VOLTAGE (V) LED EFFICIENCY vs. LED CURRENT (6 WLEDs) LED EFFICIENCY vs. LED CURRENT (6 WLEDs) 85 80 VIN = 3.
PAGE 5
Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package LED AND BOOST EFFICIENCY vs. INPUT VOLTAGE IN CURRENT (IIN) vs.
PAGE 6
Typical Operating Characteristics (continued) (Circuit of Figure 5, ILED = 24.75mA, VIN = VON = 3.6V, C1 = 1µF, C2 = 1µF, TA = +25°C, unless otherwise noted.) PWM DIMMING RESPONSE (MAX8901A) SERIAL PULSE DIMMING RESPONSE (MAX8901B) MAX8901A/B toc13 MAX8901A/B toc14 2V/div VON D = 90% D = 10% VIN VCS 2V/div 0V VON 0V 50mV/div (AC-COUPLED) VIN 50mV/div (AC-COUPLED) 500mV/div VCS 1V/div 0V 0V VOUT VOUT 20mV/div fON_PWM = 100kHz, DUTY CYCLE CHANGE: 90% TO 10%, C2 = 0.
PAGE 7
Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package PIN NAME 1 OVP FUNCTION WLED Overvoltage Protection Input. OVP monitors voltage at the WLEDs. Connect OVP to the positive terminal of the output capacitor. If an OVP condition is detected, the MAX8901_ latch off. Cycle VIN or toggle VON to restart the IC. Enable and Dimming Control Input. Drive ON high to enable the IC. Drive ON low for greater than 1.33ms (typ) to shutdown the WLED current regulator.
PAGE 8
MAX8901A/MAX8901B Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package MAX8901A GND REF THERMAL SHUTDOWN IC POWER BOOST CONTROL LOGIC INTERNAL 750kHz OSC IN LX SHUTDOWN TIMER PGND OVP CS Gm D*0.5V PWM COMP ON EP Figure 2. MAX8901A Block Diagram Detailed Description The high efficiency and tiny size of the MAX8901A/ MAX8901B WLED step-up converters make them ideally suited for driving LCD backlighting in cell phones, PDAs, and other portable and handheld devices.
PAGE 9
Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package MAX8901A/MAX8901B MAX8901B GND REF THERMAL SHUTDOWN IC POWER BOOST CONTROL LOGIC INTERNAL 750kHz OSC SHUTDOWN TIMER IN LX PGND OVP CS Gm 0.5V PULSE DIMMING COMP ON EP Figure 3. MAX8901B Block Diagram The MAX8901_ feature: • Internal soft-start that gradually illuminates the WLEDs to eliminate inrush current during startup. • Input overvoltage protection (6.5V max) that prevents IC switching when exceeded.
PAGE 10
MAX8901A/MAX8901B Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package Startup and Soft-Start PWM Dimming Control (MAX8901A) The MAX8901_ use a single input (ON) to enable the IC and to control WLED intensity. After ON is driven high, the MAX8901_ enter soft-start and gradually increase the WLED current to full brightness. When the MAX8901_ are first turned on, C COMP is charged to 1.25V with a 60µA current source. When VCOMP rises above 1.
PAGE 11
Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package Current-Sense Resistor (MAX8901A Only) The MAX8901A uses a sense resistor (RCS) connected from CS to GND to program the maximum WLED current for 100% PWM duty cycle. The MAX8901A regulates VCS to 0.5V (typ) for 100% duty cycle. Calculate RCS (in ohms) using the following equation: IDIODE (RMS) = ILED × IPEAK RCS = 500 ILED(MAX) where I LED(MAX) is the maximum WLED current in milliamps.
PAGE 12
MAX8901A/MAX8901B Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package L1 22μH INPUT 2.6V TO 5.5V C1 1μF 3 LX IN 4 C2 0.1μF MAX8901A 7 C3 0.022μF 6 COMP OVP GND PGND PWM DIMMING CONTROL 2 ON EP OUTPUT UP TO 25V D1 CS 1 D2–D7 5 8 R1 (RCS) 20Ω Figure 4. MAX8901A Application Circuit L1 22μH INPUT 2.6V TO 5.5V C1 1μF 3 7 LX IN COMP SERIAL-PULSE DIMMING CONTROL OVP 6 2 PGND GND ON EP OUTPUT UP TO 25V D1 C2 1μF MAX8901B R1 0Ω C3 0.
PAGE 13
Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package Chip Information PROCESS: BiCMOS TOP VIEW CS 8 COMP GND PGND 7 6 5 Package Information MAX8901 *EP + 1 2 3 4 OVP ON IN LX TDFN-EP (2mm × 2mm) For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only.
PAGE 14
MAX8901A/MAX8901B Highest Efficiency Supply for 2 to 6 Series WLEDs in a 2mm x 2mm TDFN Package Revision History REVISION NUMBER REVISION DATE 0 8/07 1 DESCRIPTION PAGES CHANGED Initial release — 5/08 Replaced TOC 16 6 2 6/08 Updated LED current accuracy, input undervoltage lockout threshold, and input overvoltage lockout threshold.