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MAX17061ETI+-MAX17061ETI+T
8-String White LED Driver with SMBus for LCD Panel Applications
General DescriptionThe MAX17061 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 controller drives the LED
array, which can be configured for up to eight strings in parallel
and 10 LEDs per string. Each string is terminated with ballast
that achieves ±1.5% current-regulation accuracy between
strings, ensuring even LED brightness. The MAX17061 has a
wide inputvoltage range from 4.5V to 26V, and provides a fixed
25mA or adjustable 15mA to 30mA full-scale LED current.
The MAX17061 internally generates a DPWM signal for
accurate WLED dimming control. The DPWM frequency is
resistor programmable, while DPWM duty cycle is controlled
directly from an external PWM signal or through a control
word through the MAX17061’s SMBus™ interface. This
DPWM control provides a dimming range with 8-bit resolution
and supports Intel display-power-saving technology (DPST)
to maximize battery life.
The MAX17061 has multiple features to protect the controller
from fault conditions. Separate feedback loops limit the output
voltage under any circumstance, ensuring safe operation.
Once an open string is detected, the string is disabled while
other strings operate normally. The MAX17061 also features
short LED detection. The shorted strings are also disabled
after a 2ms fault blanking interval. The controller features cycle-
bycycle current limit to provide stable operation and softstart
capability. If the MAX17061 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.
The MAX17061’s step-up controller features an internal 150mΩ (typ), 45V (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
625mV (typ) at 25mA LED current helps reduce power loss
and improve efficiency. The MAX17061 features selectable
switching frequency (500kHz, 750kHz, or 1MHz), which
enables a wide variety of applications that can trade off com-
ponent size for operating frequency.
The MAX17061 is available in a thermally enhanced 28-pin, 4mm x 4mm Thin QFN package.
Applications
Features●Accurate Dimming Control Using SMBus, PWM
Interface●Dimming Range with 8-Bit Resolution●Adjustable DPWM Frequency with 1.5% Accuracy●Up to Eight Parallel Strings Multiple Series-
Connected LEDs●±1.5% Current Regulation Accuracy Between Strings●Low String Feedback Voltage: 625mV at 25mA LED
Current●Full-Scale LED Current Adjustable from 15mA to
30mA, or Preset 25mA●Open and Short LED Protections●Output Overvoltage Protection●0.15Ω Internal HV Power MOSFET (45V max)●Wide Input-Voltage Range from 4.5V to 26V●500kHz/750kHz/1MHz Selectable Switching Frequency●Small 28-Pin, 4mm x 4mm, Thin QFN package
Pin Configuration appears at end of data sheet.SMBus is a trademark of Intel Corp.●Notebook, Subnotebook, and Tablet Computer Displays●Handy Terminals
+Denotes a lead-free package.
PARTTEMP RANGEPIN-PACKAGEMAX17061ETI+-40°C to +85°C28 Thin QFN (4mm x 4mm)
FB1
CCV
PGND1, 2
VIN
LX1, 2
FB2
FB3
FB4
FB5
FB6
FB7
FB8D1
VDD
ISET
FSET
VCC
PWMIPWM
MAX17061VOUT
SCLCLK
SDADATA
OSCN.C.
GND
PWMO
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Ordering Information
Simpliied Operating Circuit
EVALUATION KIT AVAILABLE
IN to GND ..............................................................-0.3V to +28VFB_, LX_ to GND ....................................................-0.3V to +45VPGND_ to GND......................................................-0.3V to +0.3VVCC, VDD, PWMI, SDA, SCL to GND......................-0.3V to +6VISET, CCV, PWMO, FSET, OSC, OV to GND..............................................-0.3V to VCC + 0.3V
Continuous Power Dissipation (TA = +70°C)28-Pin Thin QFN (derate 16.9mW/°C above +70°C)...1667mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-60°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,
TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETERCONDITIONSMINTYPMAXUNITSIN Input Voltage Range
VIN = VCC4.55.5VCC = open5.526.0
IN Quiescent CurrentMAX17061 is enabled at
minimum brightness, no load
VIN = 26V1.242mA
VIN = VCC = 5V
IN Quiescent CurrentMAX17061 is disabled, VIN = 12V10µA
VCC Output Voltage
MAX17061 is enabled, 6V < VIN < 26V,
0 < IVCC < 10mA4.75.05.3V
MAX17061 is disabled, VIN = 12V3.904.354.80
VCC Current LimitVCC is forced to 4.5V154070mA
VCC UVLO ThresholdRising edge, typical hysteresis = 85mV4.004.254.45V
BOOST CONVERTERLX On-Resistance20mA from LX_ to PGND0.150.3Ω
LX Leakage Current45V on LX_1µA
Operating Frequency
VOSC = VCC0.91.01.1
kHzVOSC = open675750825
VOSC = GND450500550
OSC High-Level ThresholdVCC - 0.4V
OSC Midlevel Threshold1.5VCC – 2.0V
OSC Low-Level Threshold0.4V
Minimum Duty CyclePWM mode (Note 1)10%Pulse skipping, no load (Note 1)0
Maximum Duty Cycle94.095.597.0%
LX Current LimitDuty cycle = 75% (Note 1)1.6A
CONTROL INPUTSDA, SCL Logic Input-High Level2.1V
SDA, SCL Logic Input-Low Level0.8V
PWMI Logic Input-High Level2.1V
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Absolute Maximum RatingsStresses 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, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,
TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETERCONDITIONSMINTYPMAXUNITS
INPUT LEAKAGEPWMI Leakage Current-0.3+0.3µA
ISET, FSET Leakage CurrentISET , FSET to VCC+1µA
OV Leakage Current-0.1+0.1µA
SDA, SCL Input Bias Current-1+1µA
SDA Output Low-Sink CurrentVSDA = 0.4V4mA
OSC Leakage Current-3+3µA
LED CURRENTFull-Scale FB_ Output Current
ISET = VCC24.525.025.5RISET = 133kΩ28.830.031.2
RISET = 200kΩ19.320.020.7
RISET = 266kΩ14.415.015.6
ISET High-Level ThresholdVCC - 0.4V
ISET Output Voltage1.1661.2361.306V
Current Regulation Between
StringsFull brightness-1.5+1.5%
Minimum FB_ Regulation Voltage
IFB_ = 25mA475625910IFB_ = 30mA5757501100
IFB_ = 20mA380500740
IFB_ = 15mA285375560
Maximum FB_ RippleIFB_ = 20mA (COUT = 1μF, VOSC = VCC) (Note1)120200mVP/P
FB_ On-ResistanceVFB_ = 50mV (includes 10Ω sense resistor)17.528.4Ω
FB_ Leakage CurrentVFB_ = 26V, TA = +25°C1µAVFB_ = 45V, TA = +25°C2.54
FAULT PROTECTIONOV Threshold VoltageRising edge, typical hysteresis = 60mV1.1661.2361.306V
FB_ Overvoltage ThresholdVIN > 5.5V5.25.66.0V
FB_ Undervoltage Threshold130175220mV
OV Undervoltage Threshold(Boost Global Fail)4884120mV
Thermal-Shutdown Threshold(Note 1)160°C
Over current FAULT Shutdown
TimerIPEAK > 3.3A at duty = 0%88128168µs
FB_ Overvoltage Fault TimerFull brightness1.722.3ms
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Electrical Characteristics (continued)
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,
TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,
TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETERCONDITIONSMINTYPMAXUNITS
PWM FILTERPWM Output Impedance204060kΩ
DPWM Oscillator Frequency
RFSET = 464kΩ197200203HzRFSET = 113kΩ750785820
RFSET = 65kΩ1.2701.3351.400kHzRFSET = 42kΩ2
PWMI Input-Frequency Range510100kHz
PWMI Full-Range Accuracy5LSB
PWMI Brightness Setting
PWMI duty cycle = 100%98100PWMI duty cycle = 50%485052
PWMI duty cycle = 0%2.62.72.8
SMBus TIMING SPECIFICATIONSMBus FrequencyFSMB10100kHz
Bus Free TimeTBUF4.7µs
START Condition Hold
Time from SCLTHD:STA4µs
START Condition Setup
Time from SCLTSU:STA4.7µs
STOP Condition Setup
Time from SCLTSU:STO4µs
SDA Hold Time from SCLTHD:DAT300ns
SDA Setup Time from SCLTSU:DAT250ns
SCL Low PeriodTLOW4.7µs
SCL High PeriodTHIGH4µs
PARAMETERCONDITIONSMINTYPMAXUNITSIN Input Voltage RangeVIN = VCC4.55.5VVCC = open5.526.0
IN Quiescent Current
MAX17061 is enabled at
minimum brightness, no load
VIN = 26V2mAVIN = VCC = 5V2
MAX17061 is disabled, VIN = 12V10µA
VCC Output Voltage
MAX17061 is enabled, 6V < VIN < 26V,
0 < IVCC < 10mA4.75.3V
MAX17061 is disabled, VIN = 12V3.94.8
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Electrical Characteristics (continued)
Electrical Characteristics
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,
TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETERCONDITIONSMINTYPMAXUNITS
BOOST CONVERTERLX On-Resistance20mA from LX_ to PGND0.3Ω
LX Leakage Current45V on LX_1µA
Operating Frequency
VOSC = VCC0.891.10MHz
VOSC = open675825kHz
VOSC = GND450550kHz
OSC High-Level ThresholdVCC - 0.4V
OSC Midlevel Threshold1.5VCC – 2.0V
OSC Low-Level Threshold0.4V
Maximum Duty Cycle9497%
LX Current LimitDuty cycle = 75%1.6A
CONTROL INPUTSDA, SCL Logic Input-High Level2.1V
SDA, SCL Logic Input-Low Level0.8V
PWMI Logic Input-High Level2.1V
PWMI Logic Input-Low Level0.8V
INPUT LEAKAGEPWMI Leakage Current-0.3+0.3µA
ISET, FSET Leakage CurrentISET , FSET to VCC+1µA
OV Leakage Current-0.1+0.1µA
SDA, SCL Input Bias Current-1+1µA
SDA Output Low-Sink CurrentVSDA = 0.4V4mA
OSC Leakage Current-3+3µA
LED CURRENTFull-Scale FB_ Output Current
ISET = VCC24.525.5RISET = 133kΩ28.631.4
RISET = 200kΩ19.021.0
RISET = 266kΩ14.315.7
ISET High-Level ThresholdVCC - 0.4V
ISET Output Voltage1.1661.306V
Current Regulation Between
StringsFull brightness-1.5+1.5%
Minimum FB_ Regulation Voltage
IFB_ = 25mA425910
IFB_ = 30mA5751100
IFB_ = 20mA380740
IFB_ = 15mA285560
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Electrical Characteristics (continued)
Note 1: Specifications are guaranteed by design, not production tested.
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,
TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2)
PARAMETERCONDITIONSMINTYPMAXUNITS
FAULT PROTECTIONOV Threshold VoltageRising edge, typical hysteresis = 60mV1.1661.306V
FB_ Overvoltage Threshold5.26.0V
FB_ Undervoltage Threshold130220mV
OV Undervoltage Threshold(Boost Global Fail)48120mV
Over current FAULT Shutdown
TimerIPEAK > 3.3A at duty = 0%88168µs
FB_ Overvoltage Fault TimerFull brightness1.72.3ms
PWM FILTERPWM Output Impedance2060kΩ
DPWM Oscillator Frequency
RFSET = 464kΩ197203HzRFSET = 113kΩ750820
RFSET = 65kΩ1.2701.400kHzRFSET = 42kΩ
PWMI Input-Frequency Range5100kHz
PWMI Full-Range Accuracy5LSB
PWMI Brightness Setting
PWMI duty cycle = 100%98PWMI duty cycle = 50%4852
PWMI duty cycle = 0%2.62.8
SMBus TIMING SPECIFICATIONSMBus FrequencyFSMB10100kHz
Bus Free TimeTBUF4.7µs
START Condition Hold
Time from SCLTHD:STA4µs
START Condition Setup
Time from SCLTSU:STA4.7µs
STOP Condition Setup
Time from SCLTSU:STO4µs
SDA Hold Time from SCLTHD:DAT300ns
SDA Setup Time from SCLTSU:DAT250ns
SCL Low PeriodTLOW4.7µs
SCL High PeriodTHIGH4µs
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Electrical Characteristics (continued)
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND, LEDs =
10 series x 4 parallel strings, TA = +25°C, unless otherwise noted.)
LED CURRENT
vs. SMBus BRIGHTNESS SETTINGMAX17061 toc02
SMBus BRIGHTNESS SETTING
LED CURRENT (mA)
LED CURRENT
vs. PWMI DUTY CYCLE
MAX17061 toc03
PWMI DUTY CYCLE (%)
LED CURRENT (mA)100604020
SMBus = 255
SMBus = 128
LED CURRENT vs. AMBIENT TEMPERATURE
(BRIGHTNESS = 100%)MAX17061 toc04
AMBIENT TEMPERATURE (C)
LED CURRENT (mA)804020
LED CURRENT
vs. INPUT VOLTAGE
MAX17061 toc05
LED CURRENT (mA)2014118
SMBus = 0xFF
SMBus = 0x1F
INPUT VOLTAGE (V)
SUPPLY CURRENT
vs. INPUT VOLTAGEMAX17061 toc06
SUPPLY CURRENT (mA)2014118
SMBus = 255
SMBus = 0
BOOST CONVERTER EFFICIENCY
vs. INPUT VOLTAGE (BRIGHTNESS = 100%)MAX17061 toc01
INPUT VOLTAGE (V)
BOOST CONVERTER EFFICIENCY (%)161310
SHUTDOWN CURRENT
vs. INPUT VOLTAGEMAX17061 toc07
SHUTDOWN CURRENT (A)2014118
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Typical Operating Characteristics
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND, LEDs =
10 series x 4 parallel strings, TA = +25°C, unless otherwise noted.)
SWITCHING WAVEFORMS
(VIN = 7V, BRIGHTNESS = 100%)MAX17061 toc08
1s/div
VLX
20V/div
200mA/div
0mA
SWITCHING WAVEFORMS
(VIN = 20V, BRIGHTNESS = 100%)MAX17061 toc09
1s/div
VLX
20V/div
200mA/div
0mA
STARTUP WAVEFORMS
(BRIGHTNESS = 100%)MAX17061 toc10
400s/div
VLX
20V/div
1A/div
VOUT
20V/div
VCCV
2V/div
STARTUP WAVEFORMS
(SMBus = 0x04)MAX17061 toc11
400s/div
VLX
20V/div
1A/div
VOUT
20V/div
VCCV
2V/div
LED CURRENT WAVEFORMS
(SMBus = 0x80)MAX17061 toc12
VFB1
10V/div
500mA/div
ILED
20mA/div
VOUT
20V/div
0mA
0mA
LED CURRENT WAVEFORMS
(SMBus = 0x04)MAX17061 toc13
VFB1
10V/div
500mA/div
ILED
20mA/div
VOUT
20V/div
0mA
0mA
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND, LEDs =
10 series x 4 parallel strings, TA = +25°C, unless otherwise noted.)
LED-OPEN FAULT PROTECTION
(BRIGHTNESS = 100%, LED OPEN ON FB1)MAX17061 toc14
400s/div
VFB1
1V/div
IFB2
20mA/div
IFB2
10V/div
VOUT
20V/div
0mA
LED-SHORT FAULT PROTECTION
(BRT = 100%, 2 LEDs SHORT ON FB1)MAX17061 toc15
1ms/div
VFB1
5V/div
VFB2
10V/div
IFB2
20mA/div
IFB1
20mA/div
0mA
0mA
LINE TRANSIENT RESPONSE
(VIN = 12V→19V, BRIGHTNESS = 100%)MAX17061 toc16
100s/div
VOUT
20V/div
1A/div
IFB1
20mA/div
VIN
10V/div
0mA
LINE TRANSIENT RESPONSE
(VIN = 19V→12V, BRIGHTNESS = 100%)MAX17061 toc17
100s/div
VOUT
20V/div
1A/div
IFB1
20mA/div
VIN
10V/div
0mA
LED CURRENT BALANCE
vs. INPUT VOLTAGEMAX17061 toc18
LED CURRENT BALANCE (%)2014118
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Typical Operating Characteristics (continued)
DPWM10fR[]=α×Ω+γ
PINNAMEFUNCTIONFB3LED 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 VCC.FB4LED 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 VCC.GNDAnalog Ground
4, 6, 18N.C.No ConnectionFB5LED 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 VCC.FB6LED 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 VCC.FB7LED String 7 Cathode Connection. FB7 is the open-drain output of an internal regulator, which controls current through FB7. FB7 can sink up to 30mA. If unused, connect FB7 to VCC.FB8LED String 8 Cathode Connection. FB8 is the open-drain output of an internal regulator, which controls current through FB8. FB8 can sink up to 30mA. If unused, connect FB8 to VCC.OSCOscillator Frequency-Selection Pin. Connect OSC to VCC to set the step-up converter’s oscillator frequency to 1MHz. Connect OSC to GND to set the frequency to 500kHz. Float OSC to set the frequency to 750kHz.PWMI
PWM Signal Input. This PWM signal is used for brightness control in PWM mode or DPST mode. This signal is iltered and its duty cycle is converted into a digital signal to calculate DPWM duty cycle. In PWM
mode, the DPWM duty cycle equals the input PWM duty cycle. In DPST mode, the DPWM duty cycle is the
input PWM duty cycle multiplied by the SMBus brightness command.PWMOFiltered PWM Signal Output. Connect a capacitor between PWMO and GND. The capacitor forms a lowpass ilter with an internal 40kΩ (typ) resistor to ilter the PWM signal into an analog signal whose level
represents the duty-cycle information of the input PWM signal.FSET
DPWM Frequency Adjustment Pin. Connect a resistor from FSET to GND to set the internal DPWM frequency:
where: α = 10.638 γ = 58509
This DPWM signal directly chops WLED current with the calculated duty cycle for brightness control.SDASMBus Serial-Data InputSCLSMBus Serial-Clock InputLX2Boost Regulator Internal MOSFET Drain. Connect the inductor and the Schottky diode to LX2 node. LX2
should always be shorted to LX1 externally.LX1Boost Regulator Internal MOSFET Drain. Connect the inductor and the Schottky diode to LX1 node. LX1
should always be shorted to LX2 externally.PGND2Boost Regulator Power GroundPGND1Boost Regulator Power GroundINSupply Input, 4.5V to 26V. VIN biases the internal 5V linear regulator that powers the device. Bypass IN to GND directly at the pin with a 0.1μF or greater ceramic capacitor.
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Pin Description
Detailed DescriptionThe MAX17061 is a high-efficiency driver for arrays of
white LEDs. It contains a fixed-frequency currentmode
PWM step-up controller, a 5V linear regulator, dimming control circuit, SMBus interface, internal power MOSFET, and eight regulated current sources (see Figure 2). 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 MAX17061
features selectable switching frequency (500kHz, 750kHz,
or 1MHz), which allows trade-offs between external com-
ponent size and operating efficiency. The control architec-
ture automatically skips pulses at light loads to improve
efficiency and prevents overcharging the output capacitor.
WLED brightness is controlled by turning the WLEDs on
and off with a DPWM signal. The DPWM frequency can
be accurately adjusted with a resistor. The brightness of
the LEDs is proportional to the duty cycle of the DPWM
signal, which is controlled externally through either a PWM
or 2-wire SMBus-compatible interface, or both. When both
interfaces are used at the same time, the product of the
PWM duty cycle and SMBus command value is used for
the dimming control. This DPWM control scheme provides
a full dimming range with 8-bit resolution.
The MAX17061 has multiple features to protect the con-
troller from fault conditions. Separate feedback loops limit
the output voltage in all circumstances. The MAX17061 checks each FB_ voltage during the operation. If one or more strings are open, the corresponding FB_ voltages
are pulled below 175mV (typ), and open-circuit fault is
detected. As a result, the respective current sources are
disabled. When one or more LEDs are shorted and the FB_ voltage exceeds 1.1 x VCC, short fault is detected
and the respective current source is disabled. In either
LED open or short conditions, the fault strings are dis-
abled while other strings can still operate normally. The
controller features cycle-by-cycle current limit to provide
stable operation and soft-start protection. In a currentlimit condition, the controller shuts down after a 128μs over-
current fault timer expires. A thermal-shutdown circuit
provides another level of protection.
PINNAMEFUNCTIONVDDBoost Regulator MOSFET Gate Drive Supply. Bypass VDD to GND with a ceramic capacitor of 1μF or
greater.VCC
5V Linear Regulator Output. VCC provides power to the MAX17061. Bypass VCC to GND with a ceramic capacitor of 1μF or greater. If VIN is less than or equal to 5.5V, tie VCC to IN to disable internal LDO and
use external 5V supply to VCC.CCVStep-Up Converter Compensation Pin. Connect a 0.022μF ceramic capacitor and 5.1kΩ resistor from CCV to GND. When the MAX17061 shuts down, CCV is discharged to 0V through an internal 20kΩ resistor.OVOvervoltage Sense. Connect OV to the center tap of a resistive voltage-divider from VOUT to ground. The
detection threshold for voltage limiting at OV is 1.236V (typ).ISET
Full-Scale LED Current Adjustment Pin. The resistance from ISET to GND controls the full-scale current ineach LED string:
ILEDMAX = 20mA x 200kΩ/RISET
The acceptable resistance range is 133kΩ < RISET < 266kΩ, which corresponds to full-scale LED current of
30mA > ILEDMAX > 15mA. Connect ISET to VCC for a default full-scale LED current of 25mA.FB1LED String 1 Cathode Connection. FB1 is the open-drain output of an internal regulator, which controlscurrent through FB1. FB1 can sink up to 30mA. If unused, connect FB1 to VCC.FB2LED String 2 Cathode Connection. FB2 is the open-drain output of an internal regulator, which controlscurrent through FB2. FB2 can sink up to 30mA. If unused, connect FB2 to VCC.EPExposed Backside Pad. Solder to the circuit board ground plane with suficient copper connection to ensure
low thermal resistance. See the PCB Layout Guidelines section.
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
Pin Description (continued)
The MAX17061 includes a 5V linear regulator that provides
the internal bias and gate drive for the step-up controller.
When an external 5V is available, the internal LDO can be
overdriven to decrease power dissipation. Otherwise, con-nect the IN pin to an input greater than 5.5V.
Fixed-Frequency Step-Up ControllerThe MAX17061’s fixed-frequency, current-mode, stepup controller automatically chooses the lowest active FB_
voltage to regulate the output voltage. Specifically, the dif-ference between the lowest FB_ voltage and the current-
source control signal plus an offset (VSAT) is integrated
at the CCV output. The resulting error signal is compared
to the external switch current plus slope compensation to
determine the switch on-time. As the load changes, the
error amplifier sources or sinks current to the CCV output
to deliver the required peakinductor current. The slope-
compensation signal is added to the current-sense signal
to improve stability at high duty cycles.
When the input voltage is close to the output voltage, the
MAX17061 automatically skips pulses to prevent over-
charging the output capacitor. In SKIP mode, the inductor
current ramps up for a minimum on-time of approximately 90ns, and then discharges the stored energy to the output.
The switch remains off until another pulse is needed to
boost the output voltage.
Internal 5V Linear Regulator
VCC and UVLOThe MAX17061 includes an internal low-dropout linear
regulator (VCC). When VIN is higher than 5.5V, this linear
regulator generates a 5V supply to power internal PWM controller, control logic, and MOSFET driver. The VCC voltage drops to 4.35V in shutdown. If VIN is less than
or equal to 5.5V, VCC and IN can be tied together and
powered from an external 5V supply. There is an internal
diode from VCC to IN, so VIN must be greater than VCC (see Figure 3).
FB1
FSETPGND2
PGND1
VIN
7V TO 21V
LX2
FB2
FB3
FB4
FB5
FB6
FB7
FB8
10µH
0.1µF
1µF
1µF
4.7µF
VDD
OSC
GND
VCC
PWMIPWM
ISET
VCC
COUT
LX1
MAX17061VOUT
UP TO 45V
220pF464kΩ
0.022µF
5.1kΩ
CCV
SCLCLK
SDADATA
PWMO61.9kΩ
2µF
2.21MΩ
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
5V LINEAR
REGULATOR
OSCILLATORSLOPE
COMPENSATION
CLOCK
FB OVERVOLTAGE
COMPARATOR
ERROR
COMPARATOR
OUTPUT OVERVOLTAGE
COMPARATOR
VDD
LX1, 2
PGND1, 2
ERROR
AMPLIFIER
CURRENT SOURCE
FB1
GND
FB2
OV FAULT
CONTROL AND
DRIVER LOGIC
CURRENT SENSE
HVCFB6
FB5
FB4
FB3
FB2
LVC
3-LEVEL
COMPARATOR
FB7
FB8
VCC
OSC
REF ADJ
REF
VCC + 0.6V
1.236V
ISET
PWMI
PWMOMUX
0x03"1"
"< = 1"
SCL
SMBus
INTERFACE
8-BIT D/A
VSAT
DPWM SIGNAL GENERATOR
DPWM
SETTING
WLED
ON/OFF
CURRENT SOURCE
SDA
FSET
CCV
VCC
FB3CURRENT SOURCE
FB4CURRENT SOURCE
FB5CURRENT SOURCE
FB6CURRENT SOURCE
FB7CURRENT SOURCE
FB8CURRENT SOURCE
10Ω
MAX170610x020x010x00
MUX
PWM_SEL
PWM_MDDIMMING
BLOCK DIAGRAM
MAX170618-String White LED Driver with
SMBus for LCD Panel Applications
