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19-5164; Rev 0; 3/10
TION KIT EVALUA BLE AVAILA
Six-String WLED Driver with Integrated Step-Up Converter
General Description Features
S 5V to 26V Input Supply Voltage S Up to Six Parallel Strings Multiple SeriesS S S S
MAX17127
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. 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 Q2% current-regulation accuracy, ensuring even LED brightness. 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 cycleby-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 provides another level of protection. When thermal shutdown happens, the MAX17127 is latched off. The MAX17127's step-up controller features an internal 0.12I (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 resistoradjustable 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.
Connected LEDs 250kHz to 1MHz Adjustable Switching Frequency 0.12I Internal HV Power MOSFET (48V max) Low String Feedback Voltage: 480mV at 20mA LED Current Full-Scale LED Current Adjustable from 10mA to 30mA Strings 400ns Minimum String On-Time 100Hz to 25kHz PWM Input Range Open and Short LED Protection Output Overvoltage Protection Thermal Shutdown
S Q2% Current-Regulation Accuracy Between S S S S S
S Small 20-Pin, 4mm x 4mm Thin QFN Package
Ordering Information
PART MAX17127ETP+ TEMP RANGE -40C to +85C PIN-PACKAGE 20 TQFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad.
Applications
Notebook, Subnotebook, and Tablet Computer Displays Automotive Systems Handy Terminals
Simplified Operating Circuit appears at end of data sheet.
_______________________________________________________________ Maxim Integrated Products 1
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.
Six-String WLED Driver with Integrated Step-Up Converter MAX17127
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 + 0.3V SW Switch Maximum Continuous RMS Current ...................1.6A Continuous Power Dissipation (TA = +70NC) TQFN (derate 16.9mW/NC above +70NC) ..................1349mW Operating Temperature Range .......................... -40NC to +85NC Junction Temperature .....................................................+150NC Storage Temperature Range............................ -60NC to +150NC ESD HBM ................................................................................... 2kV MM ...................................................................................200V Lead Temperature (soldering, 10s) ................................+300NC Soldering Temperature (reflow) ......................................+260NC
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1. VIN = 12V, CCOMP = 0.51nF, CCOUT = 4.7F, RCOMP = 82.5k, RISET = 180k, RFSLCT = 100k, L = 10H, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER VIN Input Voltage Range VIN Quiescent Current MAX17127 is enabled, VEN = 3.3V, VIN = 26V MAX17127 is disabled, EN = AGND MAX17127 is enabled, VEN = 3.3V, 5.4V < VIN < 26V, 0A < IVDDIO < 10mA VDDIO Output Voltage MAX17127 is enabled, VEN = 3.3V, VIN = 5V, IVDDIO = 10mA, dropout condition MAX17127 is disabled, EN = AGND, 0A < IVDDIO < 50FA VDDIO Current Limit VDDIO UVLO Threshold VIN UVLO Threshold BOOST CONVERTER SW On-Resistance SW Leakage Current Operating Frequency RFSLCT Range Maximum Duty Cycle Minimum On-Time SW Current Limit CONTROL INPUT PWM, EN Logic-Input High Level PWM, EN Logic-Input Low Level EN Pulldown Resistor 120 200 2.1 0.8 280 V V kI 20mA from SW to PGND 40V on SW, TA = +25NC RFSLCT = 100kI RFSLCT = 400kI Operating range At fSW = 1MHz (Note 1) Duty cycle = 75% 3.12 0.95 0.225 90 91 95 50 3.9 80 4.7 1.0 0.25 0.12 0.25 1 1.05 0.275 500 I FA MHz kI % ns A VDDIO is forced to 4.2V Rising edge, typical hysteresis = 250mV Falling edge Rising edge 4.85 4.6 3.1 25 3.90 4.3 4.55 CONDITIONS MIN 5 2.7 5 5 4.75 3.7 45 4.00 4.5 4.75 4.1 70 4.10 4.7 4.95 V mA V V TYP MAX 26 3.2 10 5.15 V UNITS V mA FA
2
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Six-String WLED Driver with Integrated Step-Up Converter
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1. VIN = 12V, CCOMP = 0.51nF, CCOUT = 4.7F, RCOMP = 82.5k, RISET = 180k, RFSLCT = 100k, L = 10H, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER FPO OUTPUT FPO Off-Leakage Current FPO On Output-Voltage Low INPUT LEAKAGE PWM Leakage Current OVP Leakage Current LED CURRENT RISET = 120kI Full-Scale FB_ Output Current RISET = 180kI RISET = 360kI VISET < 0.7V RISET Range Current Regulation Between Strings Minimum FB_ Regulation Voltage FB_ On-Resistance FB_ Bias Current FB_ Minimum On-Time FAULT PROTECTION OVP Threshold Voltage FB_ Overvoltage Threshold FB_ Enable Threshold Voltage FB_ Open Threshold Voltage FB_ Check LED Source Current FB_ Check LED Time Thermal-Shutdown Threshold Overcurrent Fault Timer PWM CONTROL PWM Input On-Time PWM Input Frequency Range 400 0.1 25 ns kHz (Note 1) Latch-off timer 130 0.4 0.7 1.0 +150 128 Rising edge, typical hysteresis = 90mV 1.23 7 1.25 8 1.2 280 1.3 1.3 1.27 9 V V V mV mA ms NC Fs Operating range Accuracy = 3% 10mA < IFB_< 30mA IFB_ = 30mA IFB_ = 20mA IFB_ = 10mA VFB_ = 50mV (includes 10I sense resistor) VFB_ = 40V, TA = +25NC 400 29.1 19.6 9.7 0.2 100 120 -2.0 400 555 460 350 17.5 0.1 580 30 20 10 0.3 30.9 20.4 10.3 0.4 400 360 +2.0 770 670 630 28.4 1 700 I FA ns mV kI % mA TA = +25NC, VPWM = 0V, VPWM = 5V TA = +25NC, VOVP = 0V, VOVP = 5V -1 -0.1 +1 +0.1 FA FA Fault inactive, TA = +25NC ISINK = 1mA, fault active 100 0.4 nA V CONDITIONS MIN TYP MAX UNITS
MAX17127
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Six-String WLED Driver with Integrated Step-Up Converter MAX17127
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1. VIN = 12V, CCOMP = 0.51nF, CCOUT = 4.7F, RCOMP = 82.5k, RISET = 180k, RFSLCT = 100k, L = 10H, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER VIN Input Voltage Range VIN Quiescent Current MAX17127 is enabled, VEN = 3.3V, VIN = 26V MAX17127 is disabled, EN = AGND MAX17127 is enabled, VEN = 3.3V, 5.4V < VIN < 26V, 0A < IVDDIO < 10mA VDDIO Output Voltage MAX17127 is enabled , VEN = 3.3V, VIN = 5V, IVDDIO = 10mA, dropout condition EN = AGND, 0A < IVDDIO < 50FA VDDIO Current Limit VDDIO UVLO Threshold VIN UVLO Threshold BOOST CONVERTER SW On-Resistance SW Leakage Current Operating Frequency RFSLCT Operative Range Maximum Duty Cycle Boost Output Voltage Minimum On-Time CONTROL INPUT PWM, EN Logic-Input High Level PWM, EN Logic-Input Low Level EN Pulldown Resistor FPO OUTPUT FPO On Output-Voltage Low LED CURRENT RISET = 120kI Full-Scale FB_ Output Current RISET = 180kI RISET = 360kI VISET < 0.7V RISET Range Current Regulation Between Strings Operating range Accuracy = 3% 10mA < IFB_< 30mA IFB_ = 30mA Minimum FB_ Regulation Voltage IFB_= 20mA IFB_= 10mA FB_ On-Resistance FB_ Bias Current 4 VFB_= 50mV (includes 10I sense resistor) VFB_ = 40V, TA = +25NC 29.1 19.4 9.7 0.2 100 120 -2.0 400 30.9 20.6 10.3 0.4 400 360 +2.0 770 670 630 28.4 1 A mV k % mA ISINK = 1mA, fault active 0.4 V 110 2.1 0.8 290 V V k At fSW = 1MHz With suitable OVP network (Note 1) 20mA from SW to PGND 40V on SW, TA = +25NC RFSLCT = 100kI RFSLCT = 400kI 0.95 0.225 90 92 45 80 0.25 1 1.05 0.28 500 A MHz k % V ns VDDIO is forced to 4.2V Rising edge, typical hysteresis = 250mV Falling edge Rising edge 4.85 4.6 3.1 25 3.90 4.3 4.55 4.1 70 4.10 4.7 4.95 mA V V CONDITIONS MIN 5 TYP MAX 26 3.2 15 5.15 V UNITS V mA A
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Six-String WLED Driver with Integrated Step-Up Converter
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1. VIN = 12V, CCOMP = 0.51nF, CCOUT = 4.7F, RCOMP = 82.5k, RISET = 180k, RFSLCT = 100k, L = 10H, TA = -40C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER FB_ Minimum On-Time FAULT PROTECTION OVP Threshold Voltage FB_ Overvoltage Threshold FB_ Open Threshold Voltage FB_ Check LED Source Current FB_ Check LED Time Overcurrent Fault Timer PWM CONTROL PWM Input On-Time PWM Input Frequency Range Note 1: Specifications are guaranteed by design, not production tested. 400 0.1 25 ns kHz Latch-off timer Rising edge, typical hysteresis = 90mV 1.23 7 130 0.4 0.7 88 1.27 9 280 1.3 1.3 168 V V mV mA ms s CONDITIONS MIN 400 TYP MAX 700 UNITS ns
MAX17127
Typical Operating Characteristics
(Circuit of Figure 1. VIN = 12V, TA = +25NC, unless otherwise noted.)
BOOST CONVERTER EFFICIENCY vs. INPUT VOLTAGE (VS) (VOUT = 32V, IOUT = 120mA, BRIGHTNESS = 100%)
MAX17127 toc01
BOOST CONVERTER EFFICIENCY vs. BRIGHTNESS (VS = 2V, VOUT = 32V, IOUT = 120mA AT 100%)
MAX17127 toc02
92 90 88 EFFICIENCY (%) 86 84 82 80 78 5 8 11 14 17 20 23
90
80 EFFICIENCY (%)
70
60
50 26 0 20 40 60 80 100 INPUT VOLTAGE (V) BRIGHTNESS (%)
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Six-String WLED Driver with Integrated Step-Up Converter MAX17127
Typical Operating Characteristics (continued)
(Circuit of Figure 1. VIN = 12V, TA = +25NC, unless otherwise noted.)
LED CURRENT (ILED = 20mA AT 100% BRIGHTNESS) vs. INPUT VOLTAGE (VS)
MAX17127 toc04
LED CURRENT vs. BRIGHTNESS SETTING
fPWM = 200Hz
MAX17127 toc03
20
20.20
15 LED CURRENT (mA)
20.15 LED CURRENT (mA)
10
20.10
5
20.05
0 0 20 40 60 80 100 PWM DUTY CYCLE (%)
20.00 5 8 11 14 17 20 23 26 INPUT VOLTAGE (V)
LED CURRENT (ILED = 20mA AT 10% BRIGHTNESS) vs. INPUT VOLTAGE (VS)
MAX17127 toc05
IN QUIESCENT CURRENT vs. IN VOLTAGE
MAX17127 toc06
2.04
6 5 QUIESCENT CURRENT (mA) 4 3 2 1
2.02 LED CURRENT (mA)
100% BRIGHTNESS
2.00
1.98
200Hz/1% BRIGHTNESS
1.96 5 8 11 14 17 20 23 26 INPUT VOLTAGE (V)
0 5 7 11 14 17 20 23 26 IN VOLTAGE (V)
IN SHUTDOWN CURRENT vs. IN VOLTAGE
MAX17127 toc07
SWITCHING WAVEFORMS (VS = 5V, BRIGHTNESS = 100%)
VOUT = 32V, IOUT = 120mA
10 8 6 4 2 0 5
MAX17127 toc08
EN = LOW
SHUTDOWN CURRENT (A)
VLX 20V/div 0V
INDUCTOR CURRENT 500mA/div 0mA 8 11 14 17 20 23 26 1s/div
IN VOLTAGE (V)
6
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Six-String WLED Driver with Integrated Step-Up Converter
Typical Operating Characteristics (continued)
(Circuit of Figure 1. VIN = 12V, TA = +25NC, unless otherwise noted.)
SWITCHING WAVEFORMS (VS = 26V, BRIGHTNESS = 100%)
VOUT = 32V, IOUT = 120mA
VLX 20V/div 0V INDUCTOR CURRENT 200mA/div 0mA 12V 1s/div 1ms/div
MAX17127
STARTUP WAVEFORMS (BRIGHTNESS = 100%)
MAX17127 toc10
MAX17127 toc09
VEN 5V/div 0V INDUCTOR CURRENT 500mA/div 0A VLX 20V/div 0V VOUT 20V/div 0V
STARTUP WAVEFORMS (BRIGHTNESS = 20%)
MAX17127 toc11
LED CURRENT WAVEFORMS (BRIGHTNESS = 50%)
VEN 5V/div 0V INDUCTOR CURRENT 500mA/div 0A VLX 20V/div 0V VOUT 20V/div
MAX17127 toc12
VFB1 10V/div 0V ILED 20mA/div 0mA INDUCTOR CURRENT 500mA/div 0mA 1ms/div
12V 2ms/div
0V
LED CURRENT WAVEFORMS (BRIGHTNESS = 1%)
MAX17127 toc13
LED-OPEN FAULT PROTECTION (BRIGHTNESS = 100%, LED OPEN ON FB1)
MAX17127 toc14
VFB1 10V/div 0V IFB1 20mA/div 0mA INDUCTOR CURRENT 500mA/div 0mA 1ms/div
VFB1 1V/div 0V VFB2 10V/div 0V VOUT 10V/div 10V IFB2 10mA/div
0mA 20mA 200ms/div
32V
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Six-String WLED Driver with Integrated Step-Up Converter MAX17127
Typical Operating Characteristics (continued)
(Circuit of Figure 1. VIN = 12V, TA = +25NC, unless otherwise noted.)
LED-SHORT FAULT PROTECTION (BRIGHTNESS = 100%, 3 LEDs SHORT ON FB1)
MAX17127 toc15
LINE-TRANSIENT RESPONSE (VS = 9V 21V, BRIGHTNESS = 100%)
MAX17127 toc16
VFB1 10V/div 0V
9V 21V
VOUT (AC-COUPLED) 2V/div 0V VS 10V/div 0V
IFB1 50mA/div 0mA
20mA
10s/div
0A INDUCTOR CURRENT 1A/div IFB1 10mA/div 0mA 200s/div
LINE-TRANSIENT RESPONSE (VS = 21V 9V, BRIGHTNESS = 100%)
MAX17127 toc17
MAXIMUM UNBALANCE RATE BETWEEN STRING vs. BRIGHTNESS (VS = 12V, ILED = 20mA)
0V VOUT (AC-COUPLED) 1V/div VS 10V/div 0V 0A INDUCTOR CURRENT 1A/div IFB1 10mA/div 0mA
MAX17127 toc18
1.0 MAXIMUM UNBALANCE RATE (%) 0.8 0.6 0.4 0.2 0 10
9V 21V
20mA 200s/div
MAXIMUM = IFB_ - IFB(AVG) MAX % UNBALANCE RATE (%) IFB(AVG) 20 30 40 50 60 70 80 90 100 BRIGHTNESS (%)
MAXIMUM UNBALANCE RATE BETWEEN STRINGS (ILED = 20mA) vs. INPUT VOLTAGE (VS)
MAX17127 toc19
0.8
MAXIMUM UNBALANCE RATE (%)
0.7 0.6 0.5 0.4 0.3 0.2 5 MAXIMUM = IFB_ - IFB(AVG) MAX % UNBALANCE RATE (%) IFB(AVG) 8 11 14 17 20 23
26
INPUT VOLTAGE (V)
8
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Six-String WLED Driver with Integrated Step-Up Converter
Pin Configuration
PGND
MAX17127
OVP
FB1 12
15 SW 16 I.C. 17 COMP 18 VIN 19 PWM 20
14
13
FB2 11 10 9 FB3 AGND FB4 FB5 FB6
TOP VIEW
MAX17127
R_FPWM
8 7
+
1 VDDIO 2 EN 3 FSLCT 4 ISET
EP
6 5 FPO
THIN QFN (4mm x 4mm)
Pin Description
PIN 1 2 NAME VDDIO EN FUNCTION 5V Linear Regulator Output. VDDIO provides power to the MAX17127. Bypass VDDIO to AGND with a ceramic capacitor of 1FF or greater. Enable Pin. EN = high enables the MAX17127. An internal 200kI (typ) pulldown resistor keeps the MAX17127 in disabled mode if the EN pin is high impedance. Oscillator Frequency-Adjustment Pin. The resistance from FSLCT to AGND sets the step-up converter's oscillator frequency: fSW = 1MHz O 100kI/RFSLCT The acceptable resistance range is 100kI < RFSLCT < 400kI, which corresponds to the switching frequency of 1MHz > fSW > 250kHz. Full-Scale LED Current-Adjustment Pin. The resistance from ISET to AGND controls the full-scale current in each LED string: ILEDMAX = 20mA O 180kI/RISET 4 ISET The acceptable resistance range is 120kI < RISET < 360kI, which corresponds to a full-scale LED current of 30mA > ILEDMAX > 10mA. Connecting ISET to AGND sets the test mode for 0.3mA (typ) full-scale LED current. 5 6 FPO FB6 Fault-Diagnostic Output. Open drain, active low. The FPO output is asserted low when the following faults occur: overcurrent fault, thermal fault, output-voltage short condition, or output overvoltage. LED String 6 Cathode Connection. FB6 is the open-drain output of an internal regulator, which controls current through FB6. FB6 can sink up to 30mA. If unused, connect FB6 to AGND.
3
FSLCT
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Six-String WLED Driver with Integrated Step-Up Converter MAX17127
Pin Description (continued)
PIN 7 8 9 10 11 12 13 14 15 16 17 18 19 20 -- NAME FB5 FB4 AGND FB3 FB2 FB1 R_FPWM OVP PGND SW I.C. COMP VIN PWM EP FUNCTION 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. 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. Analog Ground LED String 3 Cathode Connection. FB3 is the open-drain output of an internal regulator, which controls current through FB3. FB3 can sink up to 30mA. If unused, connect FB3 to AGND. LED String 2 Cathode Connection. FB2 is the open-drain output of an internal regulator, which controls current through FB2. FB2 can sink up to 30mA. If unused, connect FB2 to AGND. LED String 1 Cathode Connection. FB1 is the open-drain output of an internal regulator, which controls current through FB1. FB1 can sink up to 30mA. If unused, connect FB1 to AGND. Connect R_FPWM to AGND Overvoltage Sense. Connect OVP to the boost converter output through a resistor: VOVP = 1.25V O (1 + R1/R2 ) Boost Regulator Power Ground Boost Regulator Power Switch Node Internal Connection. Not connected externally. Step-Up Converter Compensation Pin. Connect a ceramic capacitor in series with a resistor from COMP to AGND. Supply Input. VIN biases the internal 5V linear regulator that powers the device. Bypass VIN to AGND directly at the pin with a 0.1FF or greater ceramic capacitor. PWM Signal Input. This signal is used for brightness control. The brightness is proportional to the PWM duty cycle, and the PWM signal directly controls the LED turning on/off. Exposed Backside Pad. Solder to the circuit board ground plane with sufficient copper connection to ensure low thermal resistance. See the PCB Layout Guidelines section.
10
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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 10H CIN 4.7F VIN VIN 0.1F 1F OVP ISET RISET 180kI FSLCT RFSLCT 100kI COMP AGND RCOMP 82.5kI CCOMP 510pF R2 71.5kI VDDIO SW PGND
MAX17127
and Table 2 lists the contact information for component suppliers.
VS 5V TO 26V
D1 COUT 4.7F R1 2.21MI
MAX17127 I.C. EN PWM R_FPWM FB1 FB2 FB3 FB4 FB5 FPO EP FB6
3.3V 10kI FAULT INDICATOR
Figure 1. Typical Operating Circuit
Table 1. Component List
DESIGNATION CIN DESCRIPTION 4.7FF Q10%, 25V X5R ceramic capacitor (1206) Murata GRM319R61E475KA12D 2.2FF Q20%, 50V X7R ceramic capacitors (1206) Murata GRM31CR71H225K 2A, 40V Schottky diode (M-flat) Toshiba CMS11 DESIGNATION L1 DESCRIPTION 10FH, 1.2A power inductor Sumida CR6D09HPNP-100MC TDK VLP6810T-100M1R2 3.2V (typ), 3.5V (max) at 20mA Nichia NSSW008C
C1, C2
White LED
D1
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Six-String WLED Driver with Integrated Step-Up Converter MAX17127
Table 2. Component Suppliers
SUPPLIER Murata Electronics North America, Inc. Nichia Corp. Sumida Corp. Toshiba America Electronic Components, Inc. Vishay PHONE 770-436-1300 248-352-6575 847-545-6700 949-455-2000 203-268-6261 WEBSITE www.murata.com www.nichia.com www.sumida.com www.toshiba.com/taec www.vishay.com
EN
FAULT CONTROL
1.25V OVP SW N
VIN VDDIO
5V LINEAR REGULATOR
ERROR COMPARATOR
CONTROL AND DRIVER LOGIC CURRENT SENSE 8V
VDDIO FSLCT OSCILLATOR SLOPE COMPENSATION
PGND
TO FAULT CONTROL ERROR AMPLIFIER COMP
Gm
OVERVOLTAGE COMPARATOR OVP 1.25V CLAMP ERROR AMPLIFIER
Gm
HVC S&H LVC
FB6 FB5 FB4 FB3 FB2
VSAT
FB1 ISET ISET
EN
N
EN
MAX17127 PWM CONTROL AGND
PWM R_FPWM I.C. FPO
VDDIO
CURRENT SOURCE CURRENT SOURCE FAULT CONTROL CURRENT SOURCE CURRENT SOURCE CURRENT SOURCE
FB2 FB3 FB4 FB5 FB6
Figure 2. Functional Diagram 12 _____________________________________________________________________________________
Six-String WLED Driver with Integrated Step-Up Converter
Detailed Description
The MAX17127 is a high-efficiency driver for arrays of white LEDs. It contains a fixed-frequency current-mode 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. When enabled, the step-up controller boosts the output voltage to provide sufficient headroom for the current sources to regulate their respective string currents. The MAX17127 features resistor-adjustable switching frequency (250kHz to 1MHz), which allows trade-offs between external component size and operating efficiency. The MAX17127 can implement brightness control through the PWM signal input. The 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. Separate feedback loops limit the output voltage in all circumstances. The MAX17127 checks each FB_ voltage during operation. If one or more strings are open, the corresponding FB_ voltages are pulled below 180mV (max), and an opencircuit fault is detected. As a result, the respective current sources are disabled. When one or more LEDs are shorted and the related FB_ voltage exceeds 8V, short fault is detected and the respective current source is disabled if at least one FB_ voltage is lower than the minimum FB_ regulation voltage +460mV (typ). When in LED open or short conditions, the fault string is disabled while other strings can still operate normally. The MAX17127 also includes other kinds of fault protections, which are overcurrent, thermal shutdown, and output overvoltage. The MAX17127 features cycle-bycycle current limit to provide consistent operation and soft-start protection. In an overcurrent condition, the IC latches off if the fault still exists after a 128Fs overcurrent fault timer expires. The output overvoltage is a nonlatched operation, and the step-up converter stops switching during the fault. A thermal-shutdown circuit provides another level of protection. The MAX17127 is latched off once thermal shutdown occurs. The MAX17127 includes a 5V linear regulator that provides the internal bias and gate driver for the step-up controller. The MAX17127's fixed-frequency, current-mode, stepup controller automatically chooses the lowest active FB_ voltage to regulate the feedback voltage. Specifically, the difference between the lowest FB_ voltage and the current source control signal plus an offset is integrated at the COMP output. The resulting error signal is compared to the internal switch current plus slope compensation to determine the switch on-time. As the load changes, the error amplifier sources or sinks current to the COMP output to deliver the required peak inductor current. The slope-compensation signal is added to the current-sense signal in order to improve stability at high duty cycles. The MAX17127 includes an internal low-dropout linear regulator (VDDIO). When VIN is higher than 5.0V, this linear regulator generates a 5V supply to power the internal PWM controller, control logic, and MOSFET driver. The VDDIO voltage drops to 3.3V in shutdown. If 5V < VIN < 5.5V, VDDIO and VIN can be connected together and powered from an external 5V supply. There is a body diode from VDDIO to VIN, so VIN must be greater than VDDIO (see Figure 2). The MAX17127 is disabled until VDDIO exceeds the UVLO threshold. The hysteresis on UVLO is approximately 250mV. In standby mode, the internal LDO is in low-power mode with 10FA (max) input current and approximately regulated at 3.3V (typ). When EN = high, the internal LDO is enabled and regulated accurately at 5V (typ). The VDDIO pin should be bypassed to AGND with a minimum 1FF ceramic capacitor. At startup, the MAX17127 performs a diagnostic test of the LED array. In the test phase, all FB_ pins are pulled up by a given current source (0.4mA min) during 1ms (typ). If some FB_ voltage is lower than 1.2V (max), the string is considered to be unused. Therefore, when a string is not in use, it should be connected to AGND. All other strings with FB_ higher than 1.2V (max) are detected as in use. After the LED string diagnostic phases are finished, the boost converter starts. An additional 1ms after boost soft-start end is used as minimum FB_ control. The total startup time is less than 10ms, including 2ms (typ) soft-start. Figure 3 shows the sequence.
Fixed-Frequency Step-Up Controller
MAX17127
Internal 5V Linear Regulator and UVLO
Startup
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Six-String WLED Driver with Integrated Step-Up Converter MAX17127
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 1FA current-sourcing capability.
Shutdown
The boost converter switching frequency can be adjusted by the external resistor on the FSLCT pin. The switching frequency adjustable range is 250kHz to 1MHz. High-frequency (1MHz) operation optimizes the regulator for the smallest component size at the expense of efficiency due to increased switching losses. Lowfrequency (250kHz) operation offers the best overall efficiency, but requires larger components and PCB area.
Frequency Selection
VIN
0V VOUT
ILED 0V
VEN 0V VDDIO 0V CHECK LED STEP-UP REGULATOR SOFT-START MIN FB_ CONTROL (1ms)
Figure 3. Startup Sequence
14
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Six-String WLED Driver with Integrated Step-Up Converter
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 high-voltage output. When the OVP pin voltage, VOVP, exceeds 1.25V (typ), a comparator turns off the internal power MOSFET. This step-up regulator switch is reenabled after the VOVP drops 90mV (typ hysteresis) below the protection threshold. This overvoltage-protection feature ensures the step-up regulator fail-safe operation when the LED strings are disconnected from the output. Maintaining uniform LED brightness and dimming capability is critical for backlight applications. The MAX17127 is equipped with a bank of six matched current sources. These specialized current sources are accurate within P 3% and match each other within 2%. They can be switched on and off at PWM frequencies of up to 25kHz. LED full-scale current is set through the ISET pin (10mA < ILED < 30mA). The minimum voltage drop across each current source is 480mV (typ) when the LED current is 20mA. The lowvoltage drop helps reduce dissipation while maintaining sufficient compliance to control the LED current within the required tolerances. The LED current sources can be disabled by connecting the respective FB_ pin to AGND at startup. When the IC is enabled, the controller scans settings for all FB_ pins. If an FB_ pin is not connected to AGND, an internal circuit pulls this pin high, and the controller enables the corresponding current source to regulate the string current. If the FB_ pin is connected to AGND, the controller disables the corresponding current regulator. The current regulator cannot be disabled by connecting the respective FB_ pin to AGND after the IC is enabled. All FB_ pins in use are combined to extract a lowest FB_ voltage (LVC) (see Figure 2). LVC is fed into the step-up regulator's error amplifier and is used to set the output voltage.
Overvoltage Protection
LED fault open/short is detected after startup. When one or more strings fail after startup, the corresponding current source is disabled. The remaining LED strings are still operated normally. The LED open/short detection is not executed when LED on-time is less than 2Fs.
Current-Source Fault Protection
MAX17127
LED Current Sources
The MAX17127 can tolerate a slight mismatch between LED strings. When severe mismatches or WLED shorts occur, the FB_ voltages are uneven because of mismatched voltage drops across strings. At each LED turn-on, the FB_ voltage is brought down to the regulation voltage quickly. When FB_ voltage is higher than 8V (typ) after LED turn-on, an LED short is detected if at least one FB_ voltage is lower than the minimum FB_ regulation voltage +460mV (typ). The remaining LED strings can still operate normally. The LED short protection is disabled during the soft-start phase of the step-up regulator. Open Current-Source Protection The MAX17127 step-up regulator output voltage is regulated according to the minimum FB_ voltages on all the strings in use. If one or more strings are open, the respective FB_ pins are pulled to ground. For any FB_ lower than 180mV, the corresponding current source is disabled. The remaining LED strings can still operate normally. If all strings in use are open, the MAX17127 shuts the step-up regulator down. The fault conditions trigger FPO function and pull the FPO pin low. Table 3 shows the state of the FPO pin with different fault conditions. The MAX17127 performs brightness control with a PWM input signal. Dimming duty cycle and frequency of current sources follow the signal at the PWM pin directly.
FPO Function
Dimming Control
Table 3. FPO Function Table
FAULT CONDITION THERMAL FAULT LATCHED FPO PIN STATE Yes Low OUTPUT OVERVOLTAGE No (stop switching) Low INPUT OVERCURRENT Yes (after time expires) Low
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Six-String WLED Driver with Integrated Step-Up Converter MAX17127
Full-Scale and Low-Level LED Current The full-scale LED current is set by:
ILED_MAX = 20mA x 180k RISET
The controller can also operate in discontinuous conduction mode (DCM). In this mode, the inductor value can be lower, but the peak inductor current is higher than in CCM. In DCM, the maximum inductor value is calculated with the following equation: VIN(MIN) L DCM(MAX) = 1 - VOUT(MAX) + VDIODE x VIN(MIN) 2 x 2 x fSW(MAX) x VOUT(MAX) x IOUT(MAX)
The acceptable resistance range for ISET is 120kI < RISET < 360kI, 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 +150NC (typ), the controller and current sources shut down. When the thermal shutdown happens, the FPO output pin is asserted low. The controller and current sources do not restart until the next enable signal is sent or input supply is recycled.
Thermal Shutdown
where the LDCM(MAX) is the maximum inductor value for DCM, E is the nominal regulator efficiency (85%), and IOUT(MAX) is the maximum output current. The output current capability of the step-up regulator is a function of current limit, input voltage, operating frequency, and inductor value. Because the slope compensation is used to stabilize the feedback loop, the inductor current limit depends on the duty cycle, and is determined with the following equation:
SF ILIM = R x 0.97, when D < 30% S SF I = x (1.27-D), when D > 30% LIM RS
Design Procedure
All MAX17127 designs should be prototyped and tested prior to production. External component value choice is primarily dictated by the output voltage and the maximum load current, as well as maximum and minimum input voltages. Begin by selecting an inductor value. Once the inductor is known, choose the diode and capacitors. To ensure the stable operation, the MAX17127 includes slope compensation, which sets the minimum inductor value. In continuous conduction mode (CCM), the minimum inductor value is calculated with the following equation: L CCM(MIN) = where: SF = 72mV, when VIN < 12.5V 72mV , when VIN > 12.5V SF = VIN - 12.5V 1+ 10.6V SF is a scale factor from the slope compensation depending on input voltage (this allows a higher current capability), the LCCM(MIN) is the minimum inductor value for stable operation in CCM, and RS = 15mI (typ) is the equivalent sensing scale factor from the controller's internal current-sense circuit.
Step-Up Converter Current Calculation
where SF is the scale factor from the slope compensation, 2.5A is the current limit specified at 75% duty cycle, and D is the duty cycle. The output current capability depends on the currentlimit value and operating mode. The maximum output current in CCM is governed by the following equation: 0.5 x D x VIN VIN I OUT_CCM(MAX) = ILIM - x x fSW x L VOUT where ILIM is the current limit calculated above, E is the nominal regulator efficiency (85%), and D is the duty cycle. The corresponding duty cycle for this current is: D= VOUT - VIN + VDIODE VOUT - ILIM x R ON + VDIODE
(VOUT(MAX) + VDIODE - 2 x VIN(MIN) ) x R S
2 x SF x fSW(MIN)
where VDIODE is the forward voltage of the rectifier diode and RON is the internal MOSFET's on-resistance (0.2I typ).
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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 x ILIM 2 x fSW x x (VOUT + VDIODE ) 2 x VOUT x (VOUT + VDIODE - VIN ) of inductor resistance to other power-path resistances, the best LIR can shift up or down. If the inductor resistance is relatively high, more ripples can be accepted to reduce the number of required turns and increase the wire diameter. If the inductor resistance is relatively low, increasing inductance to lower the peak current can reduce losses throughout the power path. If extremely thin high-resistance inductors are used, as is common for LCD panel applications, LIR higher than 2.0 can be chosen for DCM operating mode. Once a physical inductor is chosen, higher and lower values of the inductor should be evaluated for efficiency improvements in typical operating regions. The detailed design procedure for CCM can be described as follows. Calculate the approximate inductor value using the typical input voltage (VIN), the maximum output current (IOUT(MAX)), the expected efficiency (ETYP) taken from an appropriate curve in the Typical Operating Characteristics, and an estimate of LIR based on the above discussion: VIN(MIN) L= V OUT
2
MAX17127
The inductance, peak current rating, series resistance, and physical size should all be considered when selecting an inductor. These factors affect the converter's operating mode, efficiency, maximum output load capability, transient response time, output voltage ripple, and cost. The maximum output current, input voltage, output voltage, and switching frequency determine the inductor value. Very high inductance minimizes the current ripple, and therefore reduces the peak current, which decreases core losses in the inductor and I2R losses in the entire power path. However, large inductor values also require more energy storage and more turns of wire, which increase physical size and I2R copper losses. Low inductor values decrease the physical size but increase the current ripple and peak current. Finding the best inductor involves compromises among circuit efficiency, inductor size, and cost. In choosing an inductor, the first step is to determine the operating mode: continuous conduction mode (CCM) or discontinuous conduction mode (DCM). The MAX17127 has a fixed internal slope compensation, which requires a minimum inductor value. When CCM mode is chosen, the ripple current and the peak current of the inductor can be minimized. If a small-size inductor is required, DCM mode can be chosen. In DCM mode, the inductor value and size can be minimized, but the inductor ripple current and peak current are higher than those in CCM. The controller can be stable, independent of the internal slopecompensation mode, but there is a maximum inductor value requirement to ensure the DCM operating mode. The equations used here include a constant LIR, which is the ratio of the inductor peak-to-peak ripple current to the average DC inductor current at the full-load current. The controller operates in DCM mode when LIR is higher than 2.0, and it works in CCM mode when LIR is lower than 2.0. The best trade-off between inductor size and converter efficiency for step-up regulators generally has an LIR between 0.3 and 0.5. However, depending on the AC characteristics of the inductor core material and ratio
Inductor Selection
VOUT - VIN(MIN) TYP I OUT(MAX) x fSW LIR
The MAX17127 has a minimum inductor value limitation for stable operation in CCM mode at low-input voltage because of the internal fixed-slope compensation. The minimum inductor value for stability is calculated with the following equation: L CCM(MIN) =
(VOUT(MAX) + VDIODE - 2 x VIN(MIN) ) x R S
2 x SF x fSW(MIN)
where SF is a scale factor from slope compensation, and RS is the equivalent current-sensing scale factor (15mI typ). Choose an available inductor value from an appropriate inductor family. Calculate the maximum DC input current at the minimum input voltage VIN(MIN), using conservation of energy and the expected efficiency at that operating point (EMIN) taken from an appropriate curve in the Typical Operating Characteristics: IIN(DC,MAX) = I OUT(MAX) x VOUT VIN(MIN) x MIN
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17
Six-String WLED Driver with Integrated Step-Up Converter MAX17127
Calculate the ripple current at that operating point and the peak current required for the inductor: VIN(MIN) x VOUT(MAX) - VIN(MIN) IRIPPLE = L x VOUT(MAX) x fSW I IPEAK = IIN(DC,MAX) + RIPPLE 2 When DCM operating mode is chosen to minimize the inductor value, the calculations are different from those above in CCM mode. The maximum inductor value for DCM mode is calculated with the following equation: VIN(MIN) L DCM(MAX) = 1 - VOUT(MAX) + VDIODE x VIN(MIN) 2 x 2 x fSW(MAX) x VOUT(MAX) x IOUT(MAX) A 10FH inductor is chosen, which is higher than the minimum L that guarantees stability in CCM. The peak inductor current at minimum input voltage is calculated as follows:
IPEAK = 7V x (32V - 7V) 120mA x 32V + = 0.95A 7V x 0.85 2 x 10H x 32V x 0.9MHz
(
)
Alternatively, choose a DCM operating mode by using lower inductance and estimating efficiency of 85% at this operating point. Since DCM has higher peak inductor current at lower input, it causes current limit when the parameters are not chosen properly. Considering the case with six 10-LED strings and 20mA LED full-scale current to prevent excessive switch current from causing current limit: 7V L DCM(MAX) = 1 - 32V + 0.4V x (7V) 2 x 0.85 = 3.9H 2 x 1.1MHz x 32V x 120mA
The peak inductor current in DCM is calculated with the following equation:
I OUT(MAX) x 2 x VOUT(MAX) IPEAK = x VOUT(MAX) + VDIODE - VIN(MIN)
A 3.3FH inductor is chosen. The peak inductor current at minimum input voltage is calculated as follows:
IPEAK = 120mA x 2 x 32V x (32V + 0.4V - 7V) 3.3H x 1.1MHz x 0.85 x (32V + 0.4V) = 1.40A
(
L x fSW(MIN) x x VOUT(MAX) + VDIODE
(
)
)
The inductor's saturation current rating should exceed IPEAK, and the inductor's DC current rating should exceed IIN(DC,MAX). For good efficiency, choose an inductor with less than 0.1I series resistance. Considering the circuit with six 10-LED strings and 20mA LED full-scale current, the maximum load current (IOUT(MAX)) is 120mA with a 32V output and a minimal input voltage of 7V. Choosing a CCM operating mode with LIR = 0.7 at 1MHz and estimating efficiency of 85% at this operating point: 7V 32V - 7V 0.85 L= = 12.1H 32V 120mA x 1MHz 0.7 In CCM, the inductor has to be higher than LCCM(MIN): L CCM(MIN) =
2
The total output voltage ripple has two components: the capacitive ripple caused by the charging and discharging on the output capacitor, and the ohmic ripple due to the capacitor's equivalent series resistance (ESR): VRIPPLE = VRIPPLE(C) + VRIPPLE(ESR) VRIPPLE(C) and: VRIPPLE(ESR) IPEAKR ESR(COUT) where IPEAK is the peak inductor current (see the Inductor Selection section). The output voltage ripple should be low enough for the FB_ current-source regulation. The ripple voltage should be less than 200mVP-P. For ceramic capacitors, the output voltage ripple is typically dominated by VRIPPLE(C). I OUT(MAX) VOUT(MAX) - VIN(MIN) C OUT VOUT(MAX) x fSW
Output Capacitor Selection
(32V + 0.4V - 2 x 7V) x 13.7m = 5.5H
2 x 25.5mV x 0.9MHz
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Six-String WLED Driver with Integrated Step-Up Converter
The voltage rating and temperature characteristics of the output capacitor must also be considered. 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. Make sure that the diode's peak current rating is at least IPEAK calculated in the Inductor Selection section and that its breakdown voltage exceeds the output voltage. The overvoltage-protection circuit ensures the circuit safe operation; therefore, the controller should limit the output voltage within the ratings of all MOSFET, diode, and output capacitor components, while providing sufficient output voltage for LED current regulation. The OVP pin is connected to the center tap of a resistive voltage-divider (R1 and R2 in Figure 1) from the highvoltage output. When the controller detects the OVP pin voltage reaching the threshold VOVP_TH, typically 1.25V, overvoltage protection is activated. Hence, the step-up converter output overvoltage-protection point is: R1 VOUT(OVP) = VOVP_TH x (1 + ) R2 VOUT(OVP) depends on how many LEDs are used for each string and VOUT(OVP) = 1.25V x VOUT, generally and where VOUT is the LED's operating voltage for each string. In Figure 1, the output OVP voltage is set to: VOUT(OVP) = 1.25V x (1 + 2.21M ) = 39.71V 71.5k tion can be tolerated on CIN if IN is decoupled from CIN using an RC lowpass filter. The series/parallel configuration of the LED load and the full-scale bias current have a significant effect on regulator performance. LED characteristics vary significantly from manufacturer to manufacturer. Consult the respective LED data sheets to determine the range of output voltages for a given brightness and LED current. In general, brightness increases as a function of bias current. This suggests that the number of LEDs could be decreased if higher bias current is chosen; however, high current increases LED temperature and reduces operating life. Improvements in LED technology are resulting in devices with lower forward voltage while increasing the bias current and light output. LED manufacturers specify LED color at a given LED current. With lower LED current, the color of the emitted light tends to shift toward the blue range of the spectrum. A blue bias is often acceptable for business applications, but not for high-image-quality applications such as DVD players. Direct-DPWM dimming is a viable solution for reducing power dissipation while maintaining LED color integrity. Careful attention should be paid to switching noise to avoid other display-quality problems. Using fewer LEDs in a string improves step-up converter efficiency, and lowers breakdown voltage requirements of the external MOSFET and diode. The minimum number of LEDs in series should always be greater than maximum input voltage. If the diode voltage drop is lower than maximum input voltage, the voltage drop across the current-sense inputs (FB_) increases and causes excess heating in the IC. Between 8 and 12 LEDs in series are ideal for input voltages up to 20V.
MAX17127
Rectifier Diode Selection
LED Selection and Bias
Overvoltage-Protection Determination
The input capacitor (CIN) filters the current peaks drawn from the input supply and reduces noise injection into the IC. A 4.7FF ceramic capacitor is used in the typical operating circuit (Figure 1) because of the high source impedance seen in typical lab setups. Actual applications usually have much lower source impedance since the step-up regulator often runs directly from the output of another regulated supply. In some applications, CIN can be reduced below the values used in the typical operating circuit. Ensure a low-noise supply at IN by using adequate CIN. Alternatively, greater voltage varia-
Input Capacitor Selection
Applications Information
LED VFB_Variation The forward voltage of each white LED may vary up to 25% from part to part and the accumulated voltage difference in each string equates to additional power loss within the IC. For the best efficiency, the voltage difference between strings should be minimized. The difference between lowest voltage string and highest voltage string should be less than 8V (typ). Otherwise, the internal LED short-protection circuit disables the high FB_ voltage string.
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19
Six-String WLED Driver with Integrated Step-Up Converter MAX17127
The current through each FB_ pin is controlled only during the step-up converter's on-time. During the converter off-time, 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. Careful PCB layout is important for proper operation. Use the following guidelines for good PCB layout:
FB Pin Maximum Voltage
PCB Layout Guidelines
1) Minimize the area of high-current switching loop of rectifier diode, internal MOSFET, and output capacitor to avoid excessive switching noise. 2) Connect high-current input and output components with short and wide connections. The high-current input loop goes from the positive terminal of the input capacitor to the inductor, to the internal MOSFET, and then to the input capacitor's negative terminal. The high-current output loop is from the positive terminal of the input capacitor to the inductor, to the rectifier diode, and to the positive terminal of the output capacitors, reconnecting between the output capacitor and input capacitor ground terminals. Avoid using vias in the high-current paths. If vias are unavoidable, use multiple vias in parallel to reduce resistance and inductance.
3) Create a ground island (PGND) consisting of the input and output capacitor ground. Connect all these together with short, wide traces or a small ground plane. Maximizing the width of the power ground traces improves efficiency and reduces output voltage ripple and noise spikes. Create an analog ground island (AGND) consisting of the overvoltage detection divider (R1 and R2) ground connection; the ISET, FSLCT, COMP resistor connections; and the device's exposed backside pad. Connect the AGND and PGND islands by connecting the AGND pins directly to the exposed backside pad. Make no other connections between these separate ground planes. 4) Place the overvoltage-detection divider resistors as close to the OVP pin as possible. The divider's center trace should be kept short. Placing the resistors far away causes the sensing trace to become antennae that can pick up switching noise. Avoid running the sensing traces near SW. 5) Place the VIN pin and VDDIO pin bypass capacitors as close to the device as possible. The ground connection of the bypass capacitors should be connected directly to AGND pins with a wide trace. 6) Minimize the size of the SW node while keeping it wide and short. Keep the SW node away from the feedback node and ground. If possible, avoid running the SW node from one side of the PCB to the other. Use DC traces as a shield if necessary. Refer to the MAX17127 Evaluation Kit data sheet for an example of proper board layout.
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Six-String WLED Driver with Integrated Step-Up Converter
Simplified Operating Circuit (Direct-PWM Mode)
MAX17127
VDDIO ISET
VIN
SW PGND OVP
FSLCT
COMP AGND
MAX17127 I.C. EN PWM R_FPWM 3.3V FB1 FB2 FB3 FB4 FB5 FPO EP FB6
Chip Information
PROCESS: BiCMOS
Package Information
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. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE 20 TQFN PACKAGE CODE T2044+3 DOCUMENT NO. 21-0139
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Six-String WLED Driver with Integrated Step-Up Converter MAX17127
Revision History
REVISION NUMBER 0 REVISION DATE 3/10 Initial release DESCRIPTION PAGES CHANGED --
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
22
(c)
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 2010 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.

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