General Description
The 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.
PART TEMP RANGE PIN-PACKAGE
MAX17061ETI+ -40°C to +85°C 28 Thin QFN (4mm x 4mm)
FB1
CCV
PGND1, 2
IN
VIN
LX1, 2
OV
FB2
FB3
FB4
FB5
FB6
FB7
FB8
L1 D1
VDD
ISET
FSET
VCC
PWMIPWM
R1
R2
MAX17061
VOUT
SCLCLK
SDADATA
OSCN.C.
GND
PWMO
EP
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
19-3211; Rev 1; 4/14
Ordering Information
Simplied Operating Circuit
EVALUATION KIT AVAILABLE
IN to GND ..............................................................-0.3V to +28V
FB_, LX_ to GND ....................................................-0.3V to +45V
PGND_ to GND......................................................-0.3V to +0.3V
VCC, VDD, PWMI, SDA, SCL to GND......................-0.3V to +6V
ISET, 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.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
IN Input Voltage Range VIN = VCC 4.5 5.5 V
VCC = open 5.5 26.0
IN Quiescent Current MAX17061 is enabled at
minimum brightness, no load
VIN = 26V 1.24 2 mA
VIN = VCC = 5V
IN Quiescent Current MAX17061 is disabled, VIN = 12V 10 µA
VCC Output Voltage
MAX17061 is enabled, 6V < VIN < 26V,
0 < IVCC < 10mA 4.7 5.0 5.3 V
MAX17061 is disabled, VIN = 12V 3.90 4.35 4.80
VCC Current Limit VCC is forced to 4.5V 15 40 70 mA
VCC UVLO Threshold Rising edge, typical hysteresis = 85mV 4.00 4.25 4.45 V
BOOST CONVERTER
LX On-Resistance 20mA from LX_ to PGND 0.15 0.3 Ω
LX Leakage Current 45V on LX_ 1 µA
Operating Frequency
VOSC = VCC 0.9 1.0 1.1
kHzVOSC = open 675 750 825
VOSC = GND 450 500 550
OSC High-Level Threshold VCC - 0.4 V
OSC Midlevel Threshold 1.5 VCC – 2.0 V
OSC Low-Level Threshold 0.4 V
Minimum Duty Cycle PWM mode (Note 1) 10 %
Pulse skipping, no load (Note 1) 0
Maximum Duty Cycle 94.0 95.5 97.0 %
LX Current Limit Duty cycle = 75% (Note 1) 1.6 A
CONTROL INPUT
SDA, SCL Logic Input-High Level 2.1 V
SDA, SCL Logic Input-Low Level 0.8 V
PWMI Logic Input-High Level 2.1 V
PWMI Logic Input-Low Level 0.8 V
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
www.maximintegrated.com Maxim Integrated
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2
Absolute Maximum Ratings
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, 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.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
INPUT LEAKAGE
PWMI Leakage Current -0.3 +0.3 µA
ISET, FSET Leakage Current ISET , FSET to VCC +1 µA
OV Leakage Current -0.1 +0.1 µA
SDA, SCL Input Bias Current -1 +1 µA
SDA Output Low-Sink Current VSDA = 0.4V 4 mA
OSC Leakage Current -3 +3 µA
LED CURRENT
Full-Scale FB_ Output Current
ISET = VCC 24.5 25.0 25.5
mA
RISET = 133kΩ 28.8 30.0 31.2
RISET = 200kΩ 19.3 20.0 20.7
RISET = 266kΩ 14.4 15.0 15.6
ISET High-Level Threshold VCC - 0.4 V
ISET Output Voltage 1.166 1.236 1.306 V
Current Regulation Between
Strings Full brightness -1.5 +1.5 %
Minimum FB_ Regulation Voltage
IFB_ = 25mA 475 625 910
mV
IFB_ = 30mA 575 750 1100
IFB_ = 20mA 380 500 740
IFB_ = 15mA 285 375 560
Maximum FB_ Ripple IFB_ = 20mA (COUT = 1μF, VOSC = VCC) (Note1) 120 200 mVP/P
FB_ On-Resistance VFB_ = 50mV (includes 10Ω sense resistor) 17.5 28.4 Ω
FB_ Leakage Current VFB_ = 26V, TA = +25°C 1 µA
VFB_ = 45V, TA = +25°C 2.5 4
FAULT PROTECTION
OV Threshold Voltage Rising edge, typical hysteresis = 60mV 1.166 1.236 1.306 V
FB_ Overvoltage Threshold VIN > 5.5V 5.2 5.6 6.0 V
FB_ Undervoltage Threshold 130 175 220 mV
OV Undervoltage Threshold
(Boost Global Fail) 48 84 120 mV
Thermal-Shutdown Threshold (Note 1) 160 °C
Over current FAULT Shutdown
Timer IPEAK > 3.3A at duty = 0% 88 128 168 µs
FB_ Overvoltage Fault Timer Full brightness 1.7 2 2.3 ms
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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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)
PARAMETER CONDITIONS MIN TYP MAX UNITS
PWM FILTER
PWM Output Impedance 20 40 60 kΩ
DPWM Oscillator Frequency
RFSET = 464kΩ 197 200 203 Hz
RFSET = 113kΩ 750 785 820
RFSET = 65kΩ 1.270 1.335 1.400 kHz
RFSET = 42kΩ 2
PWMI Input-Frequency Range 5 10 100 kHz
PWMI Full-Range Accuracy 5 LSB
PWMI Brightness Setting
PWMI duty cycle = 100% 98 100
%PWMI duty cycle = 50% 48 50 52
PWMI duty cycle = 0% 2.6 2.7 2.8
SMBus TIMING SPECIFICATION
SMBus Frequency FSMB 10 100 kHz
Bus Free Time TBUF 4.7 µs
START Condition Hold
Time from SCL THD:STA 4 µs
START Condition Setup
Time from SCL TSU:STA 4.7 µs
STOP Condition Setup
Time from SCL TSU:STO 4 µs
SDA Hold Time from SCL THD:DAT 300 ns
SDA Setup Time from SCL TSU:DAT 250 ns
SCL Low Period TLOW 4.7 µs
SCL High Period THIGH 4 µs
PARAMETER CONDITIONS MIN TYP MAX UNITS
IN Input Voltage Range VIN = VCC 4.5 5.5 V
VCC = open 5.5 26.0
IN Quiescent Current
MAX17061 is enabled at
minimum brightness, no load
VIN = 26V 2 mA
VIN = VCC = 5V 2
MAX17061 is disabled, VIN = 12V 10 µA
VCC Output Voltage
MAX17061 is enabled, 6V < VIN < 26V,
0 < IVCC < 10mA 4.7 5.3 V
MAX17061 is disabled, VIN = 12V 3.9 4.8
VCC Current Limit VCC is forced to 4.5V 12 70 mA
VCC UVLO Threshold Rising edge, typical hysteresis = 85mV 4.00 4.45 V
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
www.maximintegrated.com Maxim Integrated
│
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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)
PARAMETER CONDITIONS MIN TYP MAX UNITS
BOOST CONVERTER
LX On-Resistance 20mA from LX_ to PGND 0.3 Ω
LX Leakage Current 45V on LX_ 1 µA
Operating Frequency
VOSC = VCC 0.89 1.10 MHz
VOSC = open 675 825 kHz
VOSC = GND 450 550 kHz
OSC High-Level Threshold VCC - 0.4 V
OSC Midlevel Threshold 1.5 VCC – 2.0 V
OSC Low-Level Threshold 0.4 V
Maximum Duty Cycle 94 97 %
LX Current Limit Duty cycle = 75% 1.6 A
CONTROL INPUT
SDA, SCL Logic Input-High Level 2.1 V
SDA, SCL Logic Input-Low Level 0.8 V
PWMI Logic Input-High Level 2.1 V
PWMI Logic Input-Low Level 0.8 V
INPUT LEAKAGE
PWMI Leakage Current -0.3 +0.3 µA
ISET, FSET Leakage Current ISET , FSET to VCC +1 µA
OV Leakage Current -0.1 +0.1 µA
SDA, SCL Input Bias Current -1 +1 µA
SDA Output Low-Sink Current VSDA = 0.4V 4 mA
OSC Leakage Current -3 +3 µA
LED CURRENT
Full-Scale FB_ Output Current
ISET = VCC 24.5 25.5
mA
RISET = 133kΩ 28.6 31.4
RISET = 200kΩ 19.0 21.0
RISET = 266kΩ 14.3 15.7
ISET High-Level Threshold VCC - 0.4 V
ISET Output Voltage 1.166 1.306 V
Current Regulation Between
Strings Full brightness -1.5 +1.5 %
Minimum FB_ Regulation Voltage
IFB_ = 25mA 425 910
mV
IFB_ = 30mA 575 1100
IFB_ = 20mA 380 740
IFB_ = 15mA 285 560
Maximum FB_ Ripple IFB_ = 20mA (COUT = 1μF, VOSC = VCC) 200 mVP/P
FB_ On-Resistance VFB_ = 50mV (includes 10Ω sense resistor) 28.4 Ω
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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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)
PARAMETER CONDITIONS MIN TYP MAX UNITS
FAULT PROTECTION
OV Threshold Voltage Rising edge, typical hysteresis = 60mV 1.166 1.306 V
FB_ Overvoltage Threshold 5.2 6.0 V
FB_ Undervoltage Threshold 130 220 mV
OV Undervoltage Threshold
(Boost Global Fail) 48 120 mV
Over current FAULT Shutdown
Timer IPEAK > 3.3A at duty = 0% 88 168 µs
FB_ Overvoltage Fault Timer Full brightness 1.7 2.3 ms
PWM FILTER
PWM Output Impedance 20 60 kΩ
DPWM Oscillator Frequency
RFSET = 464kΩ 197 203 Hz
RFSET = 113kΩ 750 820
RFSET = 65kΩ 1.270 1.400 kHz
RFSET = 42kΩ
PWMI Input-Frequency Range 5 100 kHz
PWMI Full-Range Accuracy 5 LSB
PWMI Brightness Setting
PWMI duty cycle = 100% 98
%PWMI duty cycle = 50% 48 52
PWMI duty cycle = 0% 2.6 2.8
SMBus TIMING SPECIFICATION
SMBus Frequency FSMB 10 100 kHz
Bus Free Time TBUF 4.7 µs
START Condition Hold
Time from SCL THD:STA 4 µs
START Condition Setup
Time from SCL TSU:STA 4.7 µs
STOP Condition Setup
Time from SCL TSU:STO 4 µs
SDA Hold Time from SCL THD:DAT 300 ns
SDA Setup Time from SCL TSU:DAT 250 ns
SCL Low Period TLOW 4.7 µs
SCL High Period THIGH 4 µs
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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│
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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 SETTING
MAX17061 toc02
SMBus BRIGHTNESS SETTING
LED CURRENT (mA)
200 250150100500
10
15
20
25
30
0
5
LED CURRENT
vs. PWMI DUTY CYCLE
MAX17061 toc03
PWMI DUTY CYCLE (%)
LED CURRENT (mA)
80 100604020
10
15
20
25
30
0
5
0
SMBus = 255
SMBus = 128
LED CURRENT vs. AMBIENT TEMPERATURE
(BRIGHTNESS = 100%)
MAX17061 toc04
AMBIENT TEMPERATURE (C)
LED CURRENT (mA)
60 804020
24.6
25.0
24.8
25.4
25.2
25.8
25.6
26.0
24.0
24.4
24.2
0
LED CURRENT
vs. INPUT VOLTAGE
MAX17061 toc05
LED CURRENT (mA)
17 2014118
10
15
20
25
30
0
5
5
SMBus = 0xFF
SMBus = 0x1F
INPUT VOLTAGE (V)
SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX17061 toc06
SUPPLY CURRENT (mA)
17 2014118
2
3
4
5
0
1
5
SMBus = 255
SMBus = 0
INPUT VOLTAGE (V)
BOOST CONVERTER EFFICIENCY
vs. INPUT VOLTAGE (BRIGHTNESS = 100%)
MAX17061 toc01
INPUT VOLTAGE (V)
BOOST CONVERTER EFFICIENCY (%)
19161310
86
87
88
89
90
85
7
SHUTDOWN CURRENT
vs. INPUT VOLTAGE
MAX17061 toc07
SHUTDOWN CURRENT (A)
17 2014118
4
6
8
10
0
2
5
INPUT VOLTAGE (V)
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
Maxim Integrated
│
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www.maximintegrated.com
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
IL
200mA/div
0V
0mA
SWITCHING WAVEFORMS
(VIN = 20V, BRIGHTNESS = 100%)
MAX17061 toc09
1s/div
VLX
20V/div
IL
200mA/div
0V
0mA
STARTUP WAVEFORMS
(BRIGHTNESS = 100%)
MAX17061 toc10
400s/div
VLX
20V/div
IL
1A/div
VOUT
20V/div
VCCV
2V/div
0V
0V
0V
0A
STARTUP WAVEFORMS
(SMBus = 0x04)
MAX17061 toc11
400s/div
VLX
20V/div
IL
1A/div
VOUT
20V/div
VCCV
2V/div
0V
0V
0V
0A
LED CURRENT WAVEFORMS
(SMBus = 0x80)
MAX17061 toc12
2ms/div
VFB1
10V/div
IL
500mA/div
ILED
20mA/div
VOUT
20V/div
0V
0mA
0mA
0V
LED CURRENT WAVEFORMS
(SMBus = 0x04)
MAX17061 toc13
2ms/div
VFB1
10V/div
IL
500mA/div
ILED
20mA/div
VOUT
20V/div
0V
0mA
0mA
0V
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
Maxim Integrated
│
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www.maximintegrated.com
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
0V
0V
0V
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
0V
0V
0mA
0mA
LINE TRANSIENT RESPONSE
(VIN = 12V→19V, BRIGHTNESS = 100%)
MAX17061 toc16
100s/div
VOUT
20V/div
IL
1A/div
IFB1
20mA/div
VIN
10V/div
0V
0V
0A
0mA
LINE TRANSIENT RESPONSE
(VIN = 19V→12V, BRIGHTNESS = 100%)
MAX17061 toc17
100s/div
VOUT
20V/div
IL
1A/div
IFB1
20mA/div
VIN
10V/div
0V
0V
0A
0mA
LED CURRENT BALANCE
vs. INPUT VOLTAGE
MAX17061 toc18
LED CURRENT BALANCE (%)
17 2014118
-0.2
0.2
0.6
1.0
-1.0
-0.6
5
INPUT VOLTAGE (V)
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
Maxim Integrated
│
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www.maximintegrated.com
Typical Operating Characteristics (continued)
9
DPWM
10
fR[ ]
=α× Ω +γ
PIN NAME FUNCTION
1FB3 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 VCC.
2FB4 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 VCC.
3GND Analog Ground
4, 6, 18 N.C. No Connection
5FB5 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 VCC.
7FB6 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 VCC.
8FB7 LED 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.
9 FB8 LED 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.
10 OSC Oscillator 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.
11 PWMI
PWM Signal Input. This PWM signal is used for brightness control in PWM mode or DPST mode. This
signal is ltered 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.
12 PWMO
Filtered PWM Signal Output. Connect a capacitor between PWMO and GND. The capacitor forms a
lowpass lter with an internal 40kΩ (typ) resistor to lter the PWM signal into an analog signal whose level
represents the duty-cycle information of the input PWM signal.
13 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.
14 SDA SMBus Serial-Data Input
15 SCL SMBus Serial-Clock Input
16 LX2 Boost Regulator Internal MOSFET Drain. Connect the inductor and the Schottky diode to LX2 node. LX2
should always be shorted to LX1 externally.
17 LX1 Boost Regulator Internal MOSFET Drain. Connect the inductor and the Schottky diode to LX1 node. LX1
should always be shorted to LX2 externally.
19 PGND2 Boost Regulator Power Ground
20 PGND1 Boost Regulator Power Ground
21 IN Supply 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.
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
www.maximintegrated.com Maxim Integrated
│
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Pin Description
Detailed Description
The 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.
PIN NAME FUNCTION
22 VDD Boost Regulator MOSFET Gate Drive Supply. Bypass VDD to GND with a ceramic capacitor of 1μF or
greater.
23 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.
24 CCV Step-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.
25 OV Overvoltage 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).
26 ISET
Full-Scale LED Current Adjustment Pin. The resistance from ISET to GND controls the full-scale current in
each 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.
27 FB1 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 VCC.
28 FB2 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 VCC.
— EP Exposed Backside Pad. Solder to the circuit board ground plane with sufcient copper connection to ensure
low thermal resistance. See the PCB Layout Guidelines section.
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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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 Controller
The 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 UVLO
The 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).
Figure 1. Typical Operating Circuit
FB1
FSET PGND2
PGND1
IN
VIN
7V TO 21V
LX2
OV
FB2
FB3
FB4
FB5
FB6
FB7
FB8
L1
10µH
0.1µF
1µF
1µF
4.7µF
D1
VDD
OSC
GND
VCC
PWMIPWM
ISET
VCC
COUT
LX1
MAX17061
VOUT
UP TO 45V
220pF
464kΩ
0.022µF
5.1kΩ
CCV
SCLCLK
SDADATA
PWMO
EP
R2
61.9kΩ
2µF
R1
2.21MΩ
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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Figure 2. Control Circuit Block Diagram
5V LINEAR
REGULATOR
OSCILLATOR SLOPE
COMPENSATION
CLOCK
FB OVERVOLTAGE
COMPARATOR
ERROR
COMPARATOR
OUTPUT OVERVOLTAGE
COMPARATOR
OV
VDD
LX1, 2
PGND1, 2
ERROR
AMPLIFIER
CURRENT SOURCE
IN
FB1
GND
FB2
OV FAULT
CONTROL AND
DRIVER LOGIC
CURRENT SENSE
HVC FB6
FB5
FB4
FB3
FB2
LVC
3-LEVEL
COMPARATOR
gm
FB7
FB8
EN
VCC
OSC
REF ADJ
REF
VCC + 0.6V
1.236V
ISET
PWMI
PWMO
AMUX
0x03
D"1"
"< = 1"
SCL
SMBus
INTERFACE
8-BIT D/A
VSAT
DPWM SIGNAL GENERATOR
DPWM
SETTING
WLED
ON/OFF
CURRENT SOURCE
SDA
FSET
CCV
VCC
FB3
CURRENT SOURCE
FB4
CURRENT SOURCE
FB5
CURRENT SOURCE
FB6
CURRENT SOURCE
FB7
CURRENT SOURCE
FB8
CURRENT SOURCE
10Ω
MAX17061
0x02 0x01 0x00
MUX
PWM_SEL
PWM_MD
DIMMING
BLOCK DIAGRAM
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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The MAX17061 includes power-on reset (POR) and
undervoltage lockout (UVLO) features. POR resets the
fault latch and sets all the SMBus registers to their POR
values. POR occurs when VCC rises above 2.8V (typ).
The controller is disabled until VCC exceeds the UVLO
threshold of 4.25V (typ). Hysteresis on UVLO is approxi-
mately 85mV.
The VCC and VDD pins should be bypassed to GND with
a minimum 1μF ceramic capacitor.
Startup
At startup, the MAX17061 checks the OV pin to see if the
Schottky diode is open. If the OV voltage is lower than
84mV (typ), the boost converter does not start. After the
OV test is done, the MAX17061 performs a diagnostic
test of the LED array. The test is divided to two phases;
each phase takes approximately 1.024ms. In the first test
phase, all FB_ inputs are quickly discharged down to 5.6V
(typ) and then continuously discharged by 800μA (typ)
current sources. If a given FB_ voltage remains higher
than 5.6V (typ), the string is considered to be shorted.
Otherwise, if a given FB_ voltage is higher than 3V (typ),
the string is considered to be unused. Unused strings
should be tied to VCC. In the second phase, each FB_ is
precharged by an internal 400μA (typ) current source. If a
given FB_ voltage remains lower than 1V (typ), the FB_
is considered to be a short to GND and the device is dis-
abled. After the LED string diagnostic phases are finished,
the boost converter starts. The total startup time is less
than 10ms, including 4.2ms (typ) soft-start.
Shutdown
The MAX17061 can be placed into shutdown by clearing
bit 0 of the device control register (0x01). 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 regu-
lator remains on, providing a 4.35V (typ) output voltage
to VCC, with 1μA current-sourcing capability. The fault/
status register is not reset in shutdown. When bit 0 of the
device control register (0x01) is set to 1, the MAX17061
exits shutdown mode and starts. The fault/status register
is reset at startup.
Figure 3. Low-Input-Voltage Application Circuit
FB1
FSET PGND2
PGND1
IN
VIN
2.8V TO 5.5V
EXTERNAL
5V SUPPLY
LX2
OV
FB2
FB3
FB4
FB5
FB6
FB7
FB8
L1
2.2µH
0.1µF
1µF
1µF
4.7µF
D1
VDD
OSC
GND
VCC
PWMIPWM
ISET
VCC
LX1
MAX17061
VOUT
UP TO 45V
220pF
464kΩ
0.022µF
5.1kΩ
CCV
SCLCLK
SDADATA
PWMO
EP
R2
61.9kΩ
2µF
R1
2.21MΩ
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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Frequency Selection
A tri-level OSC input sets the internal oscillator frequency
for step-up converter, as shown in Table 1. High-frequency
(1MHz) operation optimizes the regulator for the small-
est component size, at the expense of efficiency due
to increased switching losses. Low-frequency (500kHz)
operation offers the best overall efficiency but requires
larger components and PCB area.
Overvoltage Protection
To protect the step-up converter when the load is open,
or the output voltage becomes excessive for any reason,
the MAX17061 features a dedicated overvoltage feed-
back input (OV). The OV pin is tied to the center tap of
a resistive voltage-divider from the high-voltage output.
When the OV pin voltage, VOV, exceeds 1.236V, a com-
parator turns off the internal power MOSFET. This step-up
converter switch is reenabled after the VOV drops 60mV
(typ) hysteresis below the protection threshold. This over-
voltage-protection feature ensures the step-up converter
fail-safe operation when the LED strings are disconnected
from the output.
LED Current Sources
Maintaining uniform LED brightness and dimming capa-
bility are critical for LCD backlight applications. The
MAX17061 is equipped with a bank of eight matched cur-
rent sources. These specialized current sources are accu-
rate to within ±1.5% between strings and can be switched
on and off within 15μs, enabling PWM frequencies of up
to 2kHz. All LED full-scale currents are identical and are
set through the ISET pin (15mA < ILED < 30mA). When
ISET is connected to VCC, the LED fullscale current is set
at the 25mA default value.
The minimum voltage drop across each current source
is approximately 625mV when the LED current is 25mA.
The low-voltage drop helps reduce dissipation while main-
taining sufficient compliance to control the LED current
within the required tolerances.
The LED current sources can be disabled by tying the
respective FB_ pin to VCC at startup. When the IC is pow-
ered up, the controller scans settings for all FB_ pins. If a
FB_ pin is not tied to VCC, an internal circuit pulls this pin low,
and the controller enables the corresponding current source
to regulate the string current. If the FB_ pin is tied to VCC,
the controller disables the corresponding current regulator.
The current regulator cannot be disabled by connecting the
respective FB_ pin to VCC after the IC is powered up.
All FB_ pins in use are combined to extract a lowest FB_
voltage (LVC) (see Figure 2). LVC is fed into the step-up con-
verter’s error amplifier and is used to set the output voltage.
Current-Source Fault Protection
The MAX17061 performs a diagnostic test at startup.
Open/short strings are disabled. LED fault open/short is
also detected after startup. When one or more strings
fails after startup, the corresponding current sources are
disabled. The remaining LED strings still operate normally.
When a fault is detected, bit 4 or/and bit 5 of the fault/sta-
tus resister are set (see the Fault/Status Register section).
Open-Current Source Protection
The MAX17061 step-up converter 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 175mV, the corresponding current source is
disabled. The unaffected LED strings still operate nor-
mally. If all strings in use are open, the MAX17061 shuts
down the step-up converter.
The MAX17061 can tolerate A slight mismatch (4.4V)
between LED strings. When severe mismatches (> 4.4V)
or WLED shorts occur, the FB_ voltages will be uneven
because mismatched voltage drops across strings. If a
given FB_ voltage is higher than 5.6V (typ) after 24μs
blanking time when LEDs are turned on, an LED short
condition is detected on the respective string. When the
short continues for greater than 2ms, the string is dis-
abled. The controller allows the unaffected LED strings to
operate normally. The LED shortprotection feature is dis-
abled during the soft-start phase of the step-up converter.
Dimming Control
The MAX17061 internally generates a DPWM signal for
accurate WLED brightness dimming control. The DPWM
frequency is adjustable through an external setting resis-
tor and has 1.5% accuracy for RFSET = 464kΩ. The duty
cycle of this DPWM signal can be controlled externally
through two interfaces: PWM and SMBus. The ISET pin
sets the amplitude of the current sources for each LED
string (Figure 4). The internal DPWM signal directly con-
trols the duty cycle of these current sources. The resulting
current is chopped and synchronized to the DPWM signal.
When filtered by the slow response time of the human
eye, the overall brightness is modulated in a consistent
flicker-free manner.
Table 1. Frequency Selection
OSC PIN CONNECTION SWITCHING FREQUENCY
(kHz)
GND 500
Open 750
VCC 1000
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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Full-Scale LED Brightness
in DPWM Dimming Control
The full-scale LED current in the DPWM dimming is deter-
mined by resistance from the ISET pin to ground:
LEDMAX ISET
20mA 200k
IR
×Ω
=
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.
The current source output is pulse-width modulated and
synchronized with a DPWM signal to reduce jitter and
flicker noise in the display.
DPWM Frequency Setting
The MAX17061 uses an internal DPWM signal to perform
dimming control. The DPWM frequency is specified by an
external resistor connected from FSET pin to GND:
9
DPWM
10
fR[ ]
=α× Ω +γ
where: α = 10.638
γ = 58509
The adjustable range for the FSET resistor, RFSET, is
from 42kΩ to 464kΩ, corresponding to the DPWM fre-
quency of 200Hz to 2kHz.
Dimming Control Interfaces
The MAX17061’s dimming control circuit consists of two
interfaces: PWM and SMBus. The block diagram of these
two input interfaces is shown in Figure 5. The dimming
can be performed in three modes: PWM, SMBus, or
DPST. In PWM mode, the brightness is adjusted by the
PWM signal applied to the PWMI pin. In SMBus mode,
the brightness is adjusted by an I2C command from uplink
processor through the 2-wire SMBus. In DPST mode, the
brightness is adjusted by the product of the PWM duty
cycle and SMBus command value. This DPWM control
provides a dimming range with 8-bit resolution down to
2.7% and supports Intel DPST to maximize battery life.
Figure 4. LED Current Control by DPWM Signal in Dimming
Figure 5. MAX17061 PWM and SMBus Interface Circuit
D = 30% D = 12.5% D = 6.25%
DPWM
0A
ILEDMAX
ILED
D = 50%
D = tON
tON
tDPWM
tDPWM
DPWM DIMMING MODE
PWMI
PWMO
BUFFER
AMUX
0x03
IDENTIFICATION
REGISTER
D1
< = 1
SCL
SMBus
INTERFACE
DPWM
SETTING
DIGITAL
MULTIPLIER
BACKLIGHT
ON/OFF
SDA
0x02 0x01 0x00
MUX
PWM_SEL
PWM_MD
SMBus AND PWM INPUT BLOCK
FAULT/STATUS
REGISTER
DEVICE
CONTROL
REGISTER
BRIGHTNESS
CONTROL
REGISTER
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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Overvoltage Protection
The SMBus interface can be used to adjust the dim-
ming, as well as shut down the MAX17061. Before the
MAX17061 receives a turn-on command from the SMBus,
it automatically remains off. In this low-power state, most
of the control circuits are turned off, and only part of LDO
is active to provide a loosely regulated output of about
4.35V on the VCC pin to power the SMBus interface. Even
in PWM dimming mode, only the PWMI interface is used
for brightness control; the MAX17061 cannot run with-
out the SMBus interface. For sister products without the
SMBus interface, contact MAXIM Integrated Products, Inc.
Dimming Control Register Descriptions
The MAX17061 includes four registers to monitor and
control brightness, fault status, identification, and operat-
ing mode. The slave address is 0b0101100.
The MAX17061 uses two multiplexers internally to direct
the dimming signal processing (Figure 5). These two
multiplexers are controlled by 2 bits of the device con-
trol register, PWM_SEL, and PWM_MD, respectively.
The PWM_SEL bit selects either the SMBus or the PWM
input to control the brightness. The PWM_MD bit selects
the mode in which the PWM input is to be interpreted.
Table 2 provides a complete setting of the three dimming
modes (X means don’t care).
In PWM mode, the output LED brightness is solely con-
trolled by the percentage duty cycle of the input signal to
PWMI. In SMBus mode, the input of PWMI has no effect
on the dimming control, and only the SMBus command to
brightness control register adjusts the output brightness.
In DPST mode, the overall brightness level is the normal-
ized product of the SMBus command setting and PWM
input duty cycle. The PWM signal starts from 100% when
operating in DPST mode.
Brightness control register: Address is 0x00. This register is both readable and writable for all 8 bits, BRT0–BRT7,
which are used to control the LED brightness level. In SMBus dimming mode, an SMBus write byte cycle to register 0x00
sets the output brightness level. The SMBus setting of 0xFF for this register sets the backlight controller to the maximum
brightness output, and 0x00 sets the minimum backlight brightness (about 2.7%). The default value for register 0x00 is
0xFF. A write byte cycle to register 0x00 has no effect when the backlight controller is in PWM mode. The SMBus read
byte cycle to register 0x00 returns the current brightness level, regardless of the dimming mode.
Device control register: Address is 0x01. This register is both readable and writable for Bit 0 to Bit 2. Bit 0, also named
BL_CTL, is used as ON/OFF control for the output LEDs. Bit 1 and Bit 2, named PWM_SEL and PWM_MD, respectively,
control the operating mode of the backlight controller. Bit 3 through Bit 7 are reserved bits. All reserved bits, return zero
when read, and are ignored by the controller when written. A value of 1 written to BL_CTL turns on the backlight in 10ms
or less after the write cycle completes. A value of zero written to BL_CTL immediately turns off the backlight.
REGISTER 0x00 BRIGHTNESS CONTROL REGISTER DEFAULT VALUE 0xFF
BRT7 BRT6 BRT5 BRT4 BRT3 BRT2 BRT1 BRT0
Bit 7 (R/W) Bit 6 (R/W) Bit 5 (R/W) Bit 4 (R/W) Bit 3 (R/W) Bit 2 (R/W) Bit 1 (R/W) Bit 0
Bit eld denitions:
BIT FIELD DEFINITION DESCRIPTION
Bit [7..0] BRT [7..0] 8-bit brightness setting, adjusting brightness levels in 256 steps, default value is 0xFF.
REGISTER 0x01 DEVICE CONTROL REGISTER DEFAULT VALUE 0x00
RESERVED RESERVED RESERVED RESERVED RESERVED PWM_MD PWM_SEL BL_CTL
Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 (R/W) Bit 1 (R/W) Bit 0 (R/W)
Bit eld denitions:
BIT FIELD DEFINITION DESCRIPTION
Bit 2 PWM_MD PWM mode select (1 = absolute brightness, 0 = % change), default = 0
Bit 1 PWM_SEL Brightness MUX select (1 = PWM pin, 0 = SMBus value), default = 0
Bit 0 BL_CTL BL on/off (1 = on, 0 = off), default = 0
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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Fault/Status Register: Address is 0x02. This register has 6 status bits that allow monitoring the backlight controller’s
operating state. Bit 6 and Bit 7 are reserved bits, and Bit 3 is the status indicator or backlight. The other 5 bits are fault
indicators. Bit 0 is a logical OR of all fault codes except LED open/short to simplify error detection. All the bits in this
register are read only. The reserved bits return a zero when read.
Identification Register: Address is 0x03. The ID register contains two bit fields to denote the manufacturer and the
silicon revision of the controller IC. The bit field widths were chosen to allow up to 32 vendors with up to eight silicon
revisions each. This register is read only.
Table 2. Operating Modes Selected by Device Control Register Bits 1 and 2
REGISTER 0x02 FAULT STATUS REGISTER DEFAULT VALUE 0x00
RESERVED RESERVED 2_CH_SD 1_CH_SD BL_STAT OV_CURR THRM_SHDN FAULT
Bit 7 (R) Bit 6 (R) Bit 5 (R) Bit 4 (R) Bit 3 (R) Bit 2 (R) Bit 1 (R) Bit 0 (R)
Bit eld denitions:
BIT FIELD DEFINITION DESCRIPTION
Bit 5 2_CH_SD Two or more LED output channels are faulted (1 = faulted, 0 = OK)
Bit 4 1_CH_SD One LED output channel is faulted (1 = faulted, 0 = OK)
Bit 3 BL_STAT Backlight status (1 = BL on, 0 = BL off)
Bit 2 OV_CURR Input overcurrent (1 = overcurrent condition, 0 = current OK)
Bit 1 THRM_SHD Thermal shutdown (1 = thermal fault, 0 = thermal OK)
Bit 0 FAULT Any fault except LED open/short occurs (logic OR of all fault conditions, 1 = fault condition,
0 = no fault)
REGISTER 0x03 ID REGISTER DEFAULT VALUE 0x80
LED PANEL MFG3 MFG2 MFG1 MFG0 REV2 REV1 REV0
Bit 7 = 1 Bit 6 (R) Bit 5 (R) Bit 4 (R) Bit 3 (R) Bit 2 (R) Bit 1 (R) Bit 0 (R)
Bit eld denitions:
BIT FIELD DEFINITION DESCRIPTION
Bit 7 LED panel Display panel using LED backlight, bit 7 = 1
Bit [6..3] MFG[3..0] Manufacturer ID; see Table 3, default = 0
Bit [2..0] REV[2..0] Silicon rev (revs 0–7 allowed for silicon spins), default = 0
PWM_MD PWM_SEL MODE DPWM DUTY-CYCLE SETTING
X 1 PWM mode PWMI input duty cycle
1 0 SMBus mode SMBus command
0 0 DPST mode Product of PWMI input duty cycle and SMBus command
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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The list of ID values for vendors is shown in Table 3.
Thermal Shutdown
The MAX17061 includes a thermal-protection circuit. When
the local IC temperature exceeds +160°C (typ), the control-
ler and current sources shut down and do not restart until
the die temperature drops by 15°C. When thermal shut-
down occurs, Bit 1 of fault/status register is set to 1.
Design Procedure
All MAX17061 designs should be prototyped and tested
prior to production. Table 4 provides a list of power com-
ponents for the typical applications circuit. Table 5 lists
component suppliers.
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 L is known, choose the
diode and capacitors.
Step-Up Converter Current Calculation
At light loads, the MAX17061 automatically skips pulses
to improve efficiency and prevent overcharging the out-
put capacitor. The output current for the converter SKIP
operation can be calculated by the following equation:
( )
22
IN ON(MIN) OSC
O(SKIP)
OUT DIODE IN
VT f
I2L V V V
××
<×× + −
where IO(SKIP) is the output current in SKIP mode, VIN is
the input voltage, TON(MIN) is the minimum on-time, and
VDIODE is the forward voltage of rectifier diode D.
Table 3. Vendor IDs
Table 4. Component List
Table 5. Component Suppliers
ID VENDOR
0 Maxim
1 Micro Semi
2 MPS
3 O2 Micro
4 TI
5 ST
6 Analog Devices
7-14 Reserved
15 Vendor ID register not implemented
SWITCHING
FREQUENCY 1MHz 1MHz
White LED Nichia NSSW008C
3.2V (typ), 3.5V (max) at 20mA
Nichia NSSW008C
3.2V (typ), 3.5V (max) at 20mA
Number of WLEDs 10 pcs x 4 strings, 25mA (max) 10 pcs x 8 strings, 25mA (max)
Input Voltage 7V to 21V 7V to 21V
Inductor
10μH, 1.2A power inductor
TDK VLP6810T-100M1R2; Sumida
CR6D09HPNP-100MC
10μH, 2.5A power inductor
TDK SLF10145T-100M2R5-PF
Input Capacitors 4.7μF ±10%, 25V X5R ceramic capacitor (1206)
Murata GRM319R61E475KA12D
10μF ±10%, 25V X5R ceramic capacitor (1206)
Murata GRM31CR61E106KA
Output Capacitor
COUT
0.33μF ±10%, 50V X7R ceramic capacitor (1206) (6x)
Murata GRM319R71H334K
TDK C3216JB1H334K
1μF ±10%, 50V X7R ceramic capacitor (1206) (4x)
Murata GRM31MR71H105KA
TDK C3216X7R1H105K
Diode Rectier 0.7A, 60V Schottky diode (US-at)
Toshiba CUS04
3A, 60V Schottky diode
Nihon EC31QS06
SUPPLIER PHONE WEBSITE
Murata 770-436-1300 www.murata.com
Nichia 248-352-6575 www.nichia.com
Sumida 847-545-6700 www.sumida.com
Toshiba 949-455-2000 www.toshiba.com/taec
Vishay 203-268-6261 www.vishay.com
MAX17061 8-String White LED Driver with
SMBus for LCD Panel Applications
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To ensure the stable operation, the MAX17061 includes
slope compensation, which sets the minimum induc-
tor value. In continuous-conduction mode (CCM), the
minimum inductor value is calculated with the following
equation:
( )
OUT(MAX) DIODE IN(MIN) S
CCM(MIN) OSC(MIN)
V V 2V R
2 24.7mV f
+ −× ×
××
where 24.7mV is a scale factor from the slope compen-
sation, the LCCM(MIN) is the minimum inductor value
for stable operation in CCM, and RS =12mΩ (typ) is the
equivalent sensing scale factor from the controller’s inter-
nal current-sense circuit.
The controller can also operate in discontinuous conduc-
tion 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:
IN(MIN)
(MAX) OUT(MAX) DIODE
2
IN(MIN)
OSC(MAX) OUT(MAX) OUT(MAX)
V
LDCM 1 VV
V
2f V I
=−
+
×η
××× ×
where the LDCM(MAX) is the maximum inductor value for
DCM, η is the nominal regulator efficiency (85%), and
IOUT(MAX) is the maximum output current.
The output current capability of the step-up converter is a
function of current limit, input voltage, operating frequen-
cy, 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:
( )
LIM S
24.7mV 0.75 D
I 1.9A R
×−
= +
where 24.7mV is the scale factor from the slope compen-
sation, 1.9A is a typical current limit 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:
IN
OUT_CCM(MAX) LIM OSC
IN
OUT
0.5 D V
II
fL
V
V
××
= −
×
× ×η
where ILIM is the current limit calculated above, η is the
nominal regulator efficiency (85%), and D is the duty
cycle. The corresponding duty cycle for this current is:
OUT IN DIODE
OUT LIM ON DIODE
V VV
DV IRV
−+
=−× +
where VDIODE is the forward voltage of the rectifier
diode and RON is the internal MOSFET’s on-resistance
(0.15Ω typ).
The maximum output current in DCM is governed by the
following equation:
( )
2
LIM OSC
OUT_DCM(MAX) OUT DIODE IN
LI f
I2V V V
× × ×η
=×+ −
Inductor Selection
The inductance, peak current rating, series resistance,
and physical size should all be considered when selecting
an inductor. These factors affect the converter’s operat-
ing mode, efficiency, maximum output load capability,
transient response time, output voltage ripple, and cost.
The maximum output current, input voltage, output volt-
age, 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
increases 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 the compromises among circuit effi-
ciency, 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 MAX17061
has a fixed internal slope compensation that requires
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 slope compensation
mode, but there is a maximum inductor value requirement
to ensure the DCM operating mode.
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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 con-
verter 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 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 diam-
eter. 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-resis-
tance 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 detail
design procedure for CCM can be described as follows:
Inductor Selection in CCM Operation
1) Calculate the approximate inductor value using the
typical input voltage (VIN), the maximum output cur-
rent (IOUT(MAX)), the expected efficiency (ηTYP) taken
from an appropriate curve in the Typical Operating
Characteristics, and an estimate of LIR based on the
above discussion:
2
IN_MIN OUT IN_MIN TYP
OUT OUT(MAX) OSC
V VV
LV I f LIR
−
η
=
×
The MAX17061 has a minimum inductor value limitation
for a 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:
( )
OUT(MAX) DIODE IN(MIN) S
CCM(MIN) OSC(MIN)
V V 2V R
L2 24.7mV f
+ −× ×
=××
where 24.7mV is a scale factor from slope compensation,
and the RS is the equivalent current-sensing scale factor
(12mΩ typ):
1) Choose an available inductor value from an appropri-
ate 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 (ηMIN) taken from an appropriate
curve in the Typical Operating Characteristics:
OUT(MAX) OUT
I N(D C,M A X ) IN(MIN) MIN
IV
IV
×
=×η
2) Calculate the ripple current at that operating point and
the peak current required for the inductor:
( )
IN(MIN) OUT(MAX) IN(MIN)
RIPPLE OUT(MAX) OSC
VV V
ILV f
×−
=××
Inductor Selection in DCM Operation
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:
The peak-inductor current in DCM is calculated with fol-
lowing equation:
IN(MIN)
DCM(MAX) OUT(MAX) DIODE
2
IN(MIN)
OSC(MAX) OUT(MAX) OUT(MAX)
RIPPLE
PEAK IN(DC,MAX)
V
L1
VV
V
2f V I
I
II 2
=−
+
×η
××× ×
= +
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 0.1Ω series resistance.
Inductor Selection Design
Examples:
Considering the Typical Operating Circuit with four 10-LED
strings and 25mA LED full-scale current, the maximum
load current (IOUT(MAX)) is 100mA with a 35.9V output
and a minimal input voltage of 7V.
Choosing a CCM operating mode with LIR = 1 at 1MHz
and estimating efficiency of 85% at this operating point:
2
7V 35.9V 7V 0.85
L 9.44 H
35.9V 100mA 1MHz 1
−
= = µ
×
In CCM, the inductor has to be higher than LCCM(MIN):
( )
CCM(MIN)
35.9V 0.4V 2 7V 12m
L 6.0 H
2 24.7mV 0.9MHz
+ −× × Ω
= = µ
××
A10μH inductor is chosen, which is higher than the mini-
mum L that guarantees stability in CCM.
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The peak-inductor current at minimum input voltage is
calculated as follows:
( )
PEAK
100mA 35.9V
I7V 0.85
7V 35.9V 7V
0.92A
2 10 H 35.9V 0.9MHz
×
=×
×−
+=
× µ× ×
Alternatively, choosing a DCM operating mode at 750kHz
and estimating efficiency of 85% at this operating point:
DCM(MAX)
2
7V
L1
35.9V 0.4V
(7V) 0.85
5.6 H
2 0.825MHz 35.9V 100mA
= −
+
×
×=µ
× ××
A 4.7μH inductor is chosen. The peak inductor current at
minimum input voltage is calculated as follows:
( )
( )
PEAK
100mA 2 35.9V 35.9V 0.4V 7V
I 1.47A
4.7uH 0.675MHz 0.85 35.9V 0.4V
×× × + −
= =
× ×× +
Output Capacitor Selection
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):
RIPPLE RIPPLE(C) RIPPLE(ESR)
OUT(MAX) OUT(MAX) IN(MIN)
RIPPLE(C) OUT OUT(MAX) OSC
VV V
IV V
VC Vf
= +
−
≈
and:
RIPPLE(ESR) PEAK ESR(COUT)
V IR≈
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 out-
put voltage ripple is typically dominated by VRIPPLE(C).
The voltage rating and temperature characteristics of the
output capacitor must also be considered. The actual
capacitance of a ceramic capacitor is reduced by DC volt-
age biasing. Ensure the selected capacitor has enough
capacitance at actual DC biasing.
Rectier Diode Selection
The MAX17061’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.
Overvoltage Protection Determination
The OV protection circuit should ensure the circuit safe
operation; therefore, the controller should limit the out-
put voltage within the ratings of all MOSFET, diode, and
output capacitor components, while providing sufficient
output voltage for LED current regulation. The OV pin is
tied to the center tap of a resistive voltage-divider (R1
and R2 in Figure 1) from the high-voltage output. When
the controller detects the OV pin voltage reaching the
threshold VOV_TH, typically 1.23V, OV protection is acti-
vated. Hence, the step-up converter output overvoltage
protection point is:
OUT(OVP) OV_TH
R1
V V1
R2
= ×+
In Figure 1, the output OVP voltage is set to:
OUT(OVP)
2.21M
V 1.236V (1 ) 45V
61.9k
Ω
= ×+ ≈
Ω
Input Capacitor Selection
The input capacitor (CIN) filters the current peaks drawn
from the input supply and reduces noise injection into
the IC. A 10μF ceramic capacitor is used in the Typical
Operating Circuit (Figure 1) because of the high source
impedance seen in typical lab setups. Actual applica-
tions 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 (Figure 1). Ensure a low-noise supply at
IN by using adequate CIN. Alternatively, greater voltage
variation can be tolerated on CIN if IN is decoupled from
CIN using an RC lowpass filter.
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LED Selection and Bias
The series/parallel configuration of the LED load and the
full-scale bias current have a significant effect or regulator
performance. LED characteristics vary significantly from
manufacturer to manufacturer. Consult the respective
LED data sheets to determine the range of output volt-
ages 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 and 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 maxi-
mum 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.
Applications Information
LED VFB_ Variation
The MAX17061 has accurate (±1.5%) matching for each
current source. However, the forward voltage of each white
LED can vary up to 25% from part to part. The accumu-
lated 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 dif-
ference between lowest voltage string and highest voltage
string should be less than 4.8V (typ). Otherwise, the inter-
nal LED shortprotection circuit disables the high FB string.
FB Pin Maximum Voltage
The current through each FB_ pin is controlled only
during the step-up converter’s on-time. During the con-
verter’s off-time, the current sources are turned off. The
output voltage does not discharge and stays high. The
MAX17061 disables the FB current source to which the
string is shorted. In this case, the step-up converter’s out-
put voltage is always applied to the disabled FB pin. The
FB_ pin can withstand 45V.
PCB Layout Guidelines
Careful PCB layout is important for proper operation. Use
the following guidelines for good PCB layout:
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 capaci-
tor to the inductor, to the internal MOSFET, 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, to the
positive terminal of the output capacitors, reconnect-
ing 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 par-
allel to reduce resistance and inductance.
3) Create a ground island (PGND) consisting of the
input and output capacitor ground and negative ter-
minal of the current-sense resistor. Connect all these
together with short, wide traces or a small ground
plane. Maximizing the width of the powerground traces
improves efficiency and reduces output-voltage ripple
and noise spikes. Create an analog ground island
(AGND) consisting of the overvoltage detection divider
ground connection, the ISET and FSET resistor con-
nections, CCV capacitor connections, and the device’s
exposed backside pad. Connect the AGND and PGND
islands by connecting the GND pins directly to the
exposed backside pad. Make no other connections
between these separate ground planes.
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4) Place the overvoltage detection divider resistors as
close as possible to the OV pin. The divider’s center
trace should be kept short. Placing the resistors far
away causes the sensing trace to become antennas
that can pick up switching noise. Avoid running the
sensing traces near LX.
5) Place IN pin bypass capacitor as close as possible to
the device. The ground connection of the IN bypass
capacitor should be connected directly to GND pins
with a wide trace.
6) Minimize the size of the LX node while keeping it wide
and short. Keep the LX node away from the feedback
node and ground. If possible, avoid running the LX
node from one side of the PCB to the other. Use DC
traces as shield if necessary.
Refer to the MAX17061 evaluation kit for an example of
proper board layout.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
28 TQFN T2844+1 21-0139 90-0035
26
27
25
24
10
9
11
FB4
N.C.
FB5
N.C.
FB6
12
FB3
PGND1
N.C.
LX1
IN
LX2
SCL
1 2
OV
4 5 6 7
2021 19 17 16 15
ISET
FB1
PWMO
PWMI
OSC
FB8
MAX17061ETI+
GND PGND2
3
18
28 8
FB2 FB7
CCV
23 13 FSET
VCC
22 14 SDA
VDD
TOP VIEW
THIN QFN
4mm x 4mm
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Chip Information
TRANSISTOR COUNT: 21,800
PROCESS: BiCMOS
Pin Conguration
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. Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
2 4/14 No /V OPNs; Removed Automotive reference from Applications section 1
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses
are implied. Maxim Integrated reserves the right to change the circuitry and specications without notice at any time. The parametric values (min and max limits)
shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.
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Revision History
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.
