Datasheet

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Simplified Operating Circuit appears at end of data sheet.

General Description

The MAX17127 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. An internal switch current-mode step-up

converter drives the LED array, which can be configured

for up to six strings in parallel and 13 LEDs per string.

Each string is terminated with ballast that achieves ±2%

current-regulation accuracy, ensuring even LED bright-

ness. The MAX17127 has a wide input voltage range

from 5V to 26V, and provides adjustable 10mA to 30mA

full-scale LED current.

The MAX17127 can implement brightness control through

the PWM signal input, and LED current is directly

controlled by the external dimming signal’s frequency and

duty cycle.

The MAX17127 has multiple features to protect the

controller from fault conditions. Once an open/short string

is detected, the fault string is disabled while other strings

can still operate normally. The controller features cycle-

by-cycle current limit to provide constant operation and

soft-start capability. If the MAX17127 is in current-limit

condition, the step-up converter is latched off after an

internal timer expires. A thermal-shutdown circuit pro-

vides another level of protection. When thermal shutdown

happens, the MAX17127 is latched off.

The MAX17127’s step-up controller features an internal

0.12Ω (typ), 48V (max) power MOSFET with local current-

sense amplifier for accurate cycle-by-cycle current limit.

This architecture greatly simplifies the external circuitry

and saves PCB space. Low-feedback voltage at each

LED string helps reduce power loss and improve efficiency.

The MAX17127 features resistor-adjustable switching

frequency from 250kHz to 1MHz, which enables a wide

variety of applications that can trade off component size

for operating frequency.

The MAX17127 is available in a thermally enhanced,

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

Features

● 5V to 26V Input Supply Voltage

● Up to Six Parallel Strings Multiple Series-Connected

LEDs

● 250kHz to 1MHz Adjustable Switching Frequency

● 0.12Ω Internal HV Power MOSFET (48V max)

● Low String Feedback Voltage: 480mV at 20mA LED

Current

● Full-Scale LED Current Adjustable from 10mA to

30mA

● ±2% Current-Regulation Accuracy Between Strings

● 400ns Minimum String On-Time

● 100Hz to 25kHz PWM Input Range

● Open and Short LED Protection

● Output Overvoltage Protection

● Thermal Shutdown

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

Applications

● Notebook, Subnotebook, and Tablet Computer

Displays

● Handy Terminals

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

*EP = Exposed pad.

PART TEMP RANGE PIN-PACKAGE

MAX17127ETP+ -40°C to +85°C 20 TQFN-EP*

MAX17127 Six-String WLED Driver with

Integrated Step-Up Converter

19-5164; Rev 1; 11/14

Ordering Information

EVALUATION KIT AVAILABLE

Summary of content (22 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX17127 Six-String WLED Driver with Integrated Step-Up Converter General Description Features The MAX17127 can implement brightness control through the PWM signal input, and LED current is directly controlled by the external dimming signal’s frequency and duty cycle. ●● ●● ●● ●● ●● ●● The MAX17127 is a high-efficiency driver for white lightemitting diodes (LEDs). It is designed for large liquidcrystal displays (LCDs) that employ an array of LEDs as the light source.
PAGE 2
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Absolute Maximum Ratings VIN to AGND .........................................................-0.3V to +30V FB_, SW to PGND.................................................-0.3V to +52V PGND to AGND.....................................................-0.3V to +0.3V VDDIO, PWM, EN, FPO, I.C. to AGND.....................-0.3V to +6V COMP, ISET, R_FPWM, OVP, FSLCT to AGND............................................... -0.3V to VDDIO + 0.
PAGE 3
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Electrical Characteristics (continued) (Circuit of Figure 1. VIN = 12V, CCOMP = 0.51nF, CCOUT = 4.7µF, RCOMP = 82.5kΩ, RISET = 180kΩ, RFSLCT = 100kΩ, L = 10µH, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN TYP MAX UNITS FPO OUTPUT FPO Off-Leakage Current Fault inactive, TA = +25°C 100 nA FPO On Output-Voltage Low ISINK = 1mA, fault active 0.
PAGE 4
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Electrical Characteristics (Circuit of Figure 1. VIN = 12V, CCOMP = 0.51nF, CCOUT = 4.7µF, RCOMP = 82.5kΩ, RISET = 180kΩ, RFSLCT = 100kΩ, L = 10µH, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS VIN Input Voltage Range VIN Quiescent Current MIN 5 TYP MAX UNITS 26 V MAX17127 is enabled, VEN = 3.3V, VIN = 26V 3.
PAGE 5
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Electrical Characteristics (continued) (Circuit of Figure 1. VIN = 12V, CCOMP = 0.51nF, CCOUT = 4.7µF, RCOMP = 82.5kΩ, RISET = 180kΩ, RFSLCT = 100kΩ, L = 10µH, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER CONDITIONS MIN IFB_ = 30mA TYP MAX 400 UNITS 770 Minimum FB_ Regulation Voltage IFB_= 20mA 670 mV IFB_= 10mA 630 FB_ On-Resistance VFB_= 50mV (includes 10W sense resistor) 28.
PAGE 6
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Typical Operating Characteristics (continued) (Circuit of Figure 1. VIN = 12V, TA = +25°C, unless otherwise noted.) 15 20.15 20.10 10 20.05 5 0 20.20 MAX17127 toc04 MAX17127 toc03 fPWM = 200Hz LED CURRENT (ILED = 20mA AT 100% BRIGHTNESS) vs. INPUT VOLTAGE (VS) LED CURRENT (mA) LED CURRENT (mA) 20 LED CURRENT vs. BRIGHTNESS SETTING 20 0 40 60 80 100 20.
PAGE 7
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Typical Operating Characteristics (continued) (Circuit of Figure 1. VIN = 12V, TA = +25°C, unless otherwise noted.
PAGE 8
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Typical Operating Characteristics (continued) (Circuit of Figure 1. VIN = 12V, TA = +25°C, unless otherwise noted.
PAGE 9
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter OVP R_FPWM FB1 FB2 TOP VIEW PGND Pin Configuration 15 14 13 12 11 SW 16 10 FB3 I.C. 17 9 AGND 8 FB4 7 FB5 6 FB6 MAX17127 COMP 18 VIN 19 3 4 ISET 5 FPO 2 FSLCT VDDIO 1 EN PWM 20 EP + THIN QFN (4mm × 4mm) Pin Description PIN NAME 1 VDDIO 2 EN 3 FSLCT FUNCTION 5V Linear Regulator Output. VDDIO provides power to the MAX17127. Bypass VDDIO to AGND with a ceramic capacitor of 1µF or greater.
PAGE 10
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Pin Description (continued) PIN NAME 7 FB5 LED String 5 Cathode Connection. FB5 is the open-drain output of an internal regulator, which controls current through FB5. FB5 can sink up to 30mA. If unused, connect FB5 to AGND. 8 FB4 LED String 4 Cathode Connection. FB4 is the open-drain output of an internal regulator, which controls current through FB4. FB4 can sink up to 30mA. If unused, connect FB4 to AGND.
PAGE 11
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Typical Operating Circuit The MAX17127 typical operating circuit is shown as Figure 1. Table 1 lists some recommended components, L1 10µH VS 5V TO 26V and Table 2 lists the contact information for component suppliers. D1 COUT 4.7µF CIN 4.7µF VIN VIN 0.1µF R1 2.21MΩ SW VDDIO PGND 1µ F OVP COMP ISET RISET 180kΩ AGND FSLCT RFSLCT 100kΩ RCOMP 82.5kΩ CCOMP 510pF R2 71.5kΩ MAX17127 I.C. EN FB1 PWM FB2 R_FPWM FB3 3.
PAGE 12
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Table 2. Component Suppliers SUPPLIER PHONE WEBSITE Murata Electronics North America, Inc. 770-436-1300 www.murata.com Nichia Corp. 248-352-6575 www.nichia.com Sumida Corp. 847-545-6700 www.sumida.com Toshiba America Electronic Components, Inc. 949-455-2000 www.toshiba.com/taec Vishay 203-268-6261 www.vishay.com EN VIN 1.
PAGE 13
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Detailed Description Fixed-Frequency Step-Up Controller The MAX17127 is a high-efficiency driver for arrays of white LEDs. It contains a fixed-frequency currentmode PWM step-up controller, a 5V linear regulator, a dimming control circuit, an internal power MOSFET, and six regulated current sources. Figure 2 shows the MAX17127 functional diagram.
PAGE 14
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Shutdown The MAX17127 can be placed into shutdown by pulling the EN pin low. When a critical failure is detected, the IC also enters shutdown mode. In shutdown mode, all functions of the IC are turned off, including the 5V linear regulator. Only a crude linear regulator remains on, providing a 3.3V (typ) output voltage to VDDIO with 1µA current-sourcing capability.
PAGE 15
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Overvoltage Protection To protect the step-up regulator when the load is open, or if the output voltage becomes excessive for any reason, the MAX17127 features a dedicated overvoltagefeedback input (OVP). The OVP pin is connected to the center tap of a resistive voltage-divider from the highvoltage output. When the OVP pin voltage (VOVP) exceeds 1.25V (typ), a comparator turns off the internal power MOSFET.
PAGE 16
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Full-Scale and Low-Level LED Current The full-scale LED current is set by: ILED_MAX = 20mA × 180kΩ R ISET The acceptable resistance range for ISET is 120kΩ < RISET < 360kΩ, which corresponds to full-scale LED current of 30mA > ILED_MAX > 10mA. The MAX17127 includes a thermal-protection circuit. When the local IC temperature exceeds +150°C (typ), the controller and current sources shut down.
PAGE 17
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter The maximum output current in DCM is governed by the following equation: I OUT_DCM(MAX) = L × ILIM 2 × f SW × η × (VOUT + VDIODE ) 2 × VOUT × (VOUT + VDIODE − VIN ) Inductor Selection The inductance, peak current rating, series resistance, and physical size should all be considered when selecting an inductor.
PAGE 18
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Calculate the ripple current at that operating point and the peak current required for the inductor: IRIPPLE = ( VIN(MIN) × VOUT(MAX) − VIN(MIN) The peak inductor current at minimum input voltage is calculated as follows: ) L × VOUT(MAX) × f SW 7V × (32V − 7V ) 120mA × 32V + = IPEAK = 0.95A 7V × 0.85 2 × 10µH × 32V × 0.
PAGE 19
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter The voltage rating and temperature characteristics of the output capacitor must also be considered. Rectifier Diode Selection The MAX17127’s high switching frequency demands a high-speed rectifier. Schottky diodes are recommended for most applications because of their fast recovery time and low forward voltage. The diode should be rated to handle the output voltage and the peak switch current.
PAGE 20
MAX17127 FB Pin Maximum Voltage The current through each FB_ pin is controlled only during the step-up converter’s on-time. During the converter offtime, the current sources are turned off. The output voltage does not discharge and stays high. The MAX17127 disables the FB_ current source, which the string is shorted. In this case, the step-up converter’s output voltage is always applied to the disabled FB_ pin. The FB_ pin can withstand 45V.
PAGE 21
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Simplified Operating Circuit (Direct-PWM Mode) VIN VDDIO SW PGND ISET OVP COMP FSLCT AGND MAX17127 I.C. EN FB1 PWM FB2 R_FPWM FB3 3.3V FB4 FB5 FPO FB6 EP Chip Information PROCESS: BiCMOS www.maximintegrated.com Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only.
PAGE 22
MAX17127 Six-String WLED Driver with Integrated Step-Up Converter Revision History REVISION NUMBER REVISION DATE 0 3/10 Initial release — 11/14 No /V OPN in Ordering Information; deleted automotive reference from Applications section 1 1 PAGES CHANGED DESCRIPTION For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.