General Description
The MAX17061 is a high-efficiency driver for white light-
emitting diodes (LEDs). It is designed for large liquid-
crystal displays (LCDs) that employ an array of LEDs as
the light source. An internal switch current-mode step-up
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 input-
voltage 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 con-
trolled directly from an external PWM signal or through a
control word through the MAX17061’s SMBus™ inter-
face. 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 con-
troller from fault conditions. Separate feedback loops
limit the output voltage under any circumstance, ensur-
ing safe operation. Once an open string is detected,
the string is disabled while other strings operate nor-
mally. The MAX17061 also features short LED detec-
tion. The shorted strings are also disabled after a 2ms
fault blanking interval. The controller features cycle-by-
cycle current limit to provide stable operation and soft-
start 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 pro-
vides another level of protection.
The MAX17061’s step-up controller features an internal
150mΩ(typ), 45V (max) power MOSFET with local cur-
rent-sense amplifier for accurate cycle-by-cycle current
limit. This architecture greatly simplifies the external cir-
cuitry 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 vari-
ety of applications that can trade off component size for
operating frequency.
The MAX17061 is available in a thermally enhanced
28-pin, 4mm x 4mm Thin QFN package.
Applications
Features
oAccurate Dimming Control Using SMBus, PWM
Interface
oDimming Range with 8-Bit Resolution
oAdjustable DPWM Frequency with 1.5% Accuracy
oUp to Eight Parallel Strings Multiple Series-
Connected LEDs
o±1.5% Current Regulation Accuracy Between
Strings
oLow String Feedback Voltage: 625mV at 25mA
LED Current
oFull-Scale LED Current Adjustable from 15mA to
30mA, or Preset 25mA
oOpen and Short LED Protections
oOutput Overvoltage Protection
o0.15ΩInternal HV Power MOSFET (45V max)
oWide Input-Voltage Range from 4.5V to 26V
o500kHz/750kHz/1MHz Selectable Switching
Frequency
oSmall 28-Pin, 4mm x 4mm, Thin QFN package
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
________________________________________________________________
Maxim Integrated Products
1
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
Simplified Operating Circuit
Ordering Information
19-3211; Rev 0; 1/08
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.
+
Denotes a lead-free package.
PART
TEMP RANGE
PIN-PACKAGE
MAX17061ETI+
-40oC to +85oC
28 Thin QFN (4mm x 4mm)
Pin Configuration appears at end of data sheet.
SMBus is a trademark of Intel Corp.
Notebook, Subnotebook,
and Tablet Computer
Displays
Automotive Systems
Handy Terminals
EVALUATION KIT
AVAILABLE
ABSOLUTE MAXIMUM RATINGS
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.)
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.
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
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
2 _______________________________________________________________________________________
PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN = VCC 4.5 5.5
IN Input Voltage Range VCC = open 5.5 26.0
V
VIN = 26V
IN Quiescent Current MAX17061 is enabled at
minimum brightness, no load VIN = VCC = 5V
1.24 2 mA
IN Quiescent Current MAX17061 is disabled, VI N
= 12V 10 µA
M AX 17061 i s enab l ed , 6V < V
I N
< 26V , 0 < IV C C
< 10m A 4.7 5.0 5.3
VCC Output Voltage MAX17061 is disabled, VI N = 12V 3.90 4.35 4.80
V
VCC Current Limit VC C
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
VOSC = VCC 0.9 1.0 1.1 MHz
VOSC = open 675 750 825Operating Frequency
VOSC = GND 450 500 550
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
PWM mode (Note 1) 10
Minimum Duty Cycle 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
_______________________________________________________________________________________ 3
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.)
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
ISET = VCC 24.5 25.0 25.5
RISET = 133kΩ 28.8 30.0 31.2
RISET = 200kΩ 19.3 20.0 20.7
Full-Scale FB_ Output Current
RISET = 266kΩ 14.4 15.0 15.6
mA
ISET High-Level Threshold
VCC -
0.4 V
ISET Output Voltage 1.166 1.236 1.306 V
C ur r ent Reg ul ati on Betw een S tr i ng s Full brightness -1.5 +1.5 %
IFB_ = 25mA 475 625 910
IFB_ = 30mA 575 750 1100
IFB_ = 20mA 380 500 740
Minimum FB_ Regulation Voltage
IFB_ = 15mA 285 375 560
mV
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
VFB_ = 26V, TA = +25°C 1
FB_ Leakage Current VFB_ = 45V, TA = +25°C 2.5 4
µA
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 cur r ent FAU LT S hutd ow n Ti m er 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
4 _______________________________________________________________________________________
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.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
PWM FILTER
PWM Output Impedance 20 40 60 kΩ
RFSET = 464kΩ 197 200 203
RFSET = 113kΩ 750 785 820
Hz
RFSET = 65kΩ 1.270 1.335 1.400
DPWM Oscillator Frequency
RFSET = 42kΩ 2
kHz
PWMI Input-Frequency Range 5 10 100 kHz
PWMI Full-Range Accuracy 5 LSB
PWMI duty cycle = 100% 98 100
PWMI duty cycle = 50% 48 50 52
PWMI Brightness Setting
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
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022µF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,
TA= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN = VCC 4.5 5.5
IN Input Voltage Range VCC = open 5.5 26.0
V
VIN = 26V 2
MAX17061 is enabled at
minimum brightness, no load VIN = VCC = 5V 2
mA
IN Quiescent Current
MAX17061 is disabled, VIN = 12V 10 µA
MAX17061 is enabled, 6V < VIN < 26V, 0 < IVCC < 10mA 4.7 5.3
VCC Output Voltage MAX17061 is disabled, VIN = 12V 3.9 4.8
V
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
_______________________________________________________________________________________ 5
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022µF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,
TA= -40°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
VOSC = VCC 0.89 1.10 MHz
VOSC = open 675 825 kHzOperating Frequency
VOSC = GND 450 560 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
S D A, S C L Log i c Inp ut- H i g h 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
ISET = VCC 24.5 25.5
RISET = 133kΩ 28.6 31.4
RISET = 200kΩ 19.0 21.0
Full-Scale FB_ Output Current
RISET = 266kΩ 14.3 15.7
mA
ISET High-Level Threshold
VCC -
0.4 V
ISET Output Voltage 1.166 1.306 V
C ur r ent Reg ul ati on Betw een S tr i ng s Full brightness -1.5 +1.5 %
IFB_ = 25mA 425 910
IFB_ = 30mA 575 1100
IFB_ = 20mA 380 740
Minimum FB_ Regulation Voltage
IFB_ = 15mA 285 560
mV
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
6 _______________________________________________________________________________________
Note 1: Specifications are guaranteed by design, not production tested.
Note 2: Specifications to -40°C are guaranteed by design, not production tested.
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, VIN = 12V, CCCV = 0.022µF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,
TA= -40°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 cur r ent FAU LT S hutd ow n Ti m er IPEAK > 3.3A at duty = 0% 88 168 µs
FB_ Overvoltage Fault Timer 1.6 2.4 ms
PWM FILTER
PWM Output Impedance 20 60 kΩ
RFSET = 464kΩ 197 203 kHz
RFSET = 113kΩ 750 820 HzDPWM Oscillator Frequency
RFSET = 65kΩ 1.27 1.40 kHz
PWMI Input Frequency Range 5 100 kHz
PWMI Full-Range Accuracy 5 LSB
PWMI duty cycle = 100% 98
PWMI duty cycle = 50% 48 52
PWMI Brightness Setting
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
_______________________________________________________________________________________
7
BOOST CONVERTER EFFICIENCY
vs. INPUT VOLTAGE (BRIGHTNESS = 100%)
MAX17061 toc01
INPUT VOLTAGE (V)
BOOST CONVERTER EFFICIENCY (%)
19161310
86
87
88
89
90
85
7
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)
SHUTDOWN CURRENT
vs. INPUT VOLTAGE
MAX17061 toc07
SHUTDOWN CURRENT (μA)
17 2014118
4
6
8
10
0
2
5
INPUT VOLTAGE (V)
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.)
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
8 _______________________________________________________________________________________
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.)
SWITCHING WAVEFORMS
(VIN = 7V, BRIGHTNESS = 100%)
MAX17061 toc08
1μs/div
VLX
20V/div
IL
200mA/div
0V
0mA
SWITCHING WAVEFORMS
(VIN = 20V, BRIGHTNESS = 100%)
MAX17061 toc09
1μs/div
VLX
20V/div
IL
200mA/div
0V
0mA
STARTUP WAVEFORMS
(BRIGHTNESS = 100%)
MAX17061 toc10
400μs/div
VLX
20V/div
IL
1A/div
VOUT
20V/div
VCCV
2V/div
0V
0V
0V
0A
STARTUP WAVEFORMS
(SMBus = 0x04)
MAX17061 toc11
400μs/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
_______________________________________________________________________________________
9
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
400μs/div
VFB1
1V/div
IFB2
20mA/div
IFB2
10V/div
VOUT
20V/div
0V
0V
0V
0mA
LINE TRANSIENT RESPONSE
(VIN = 12V→19V, BRIGHTNESS = 100%)
MAX17061 toc16
100μs/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
10 ______________________________________________________________________________________
Pin Description
PIN NAME FUNCTION
1 FB3 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.
2 FB4 LED String 4 Cathode Connection. FB4 is the open-drain output of an internal regulator, which controls
current through FB4. FB4 can sink up to 30mA. If unused, connect FB4 to VCC.
3 GND Analog Ground
4, 6, 18 N.C. No Connection
5 FB5 LED String 5 Cathode Connection. FB5 is the open-drain output of an internal regulator, which controls
current through FB5. FB5 can sink up to 30mA. If unused, connect FB5 to VCC.
7 FB6 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.
8 FB7 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 O sci l l ator Fr eq uency- S el ecti on P i n. C onnect OS C to V
C C
to set the step - up conver ter ’ s osci l l ator fr eq uency to
1M H z. C onnect O S C to G N D to set the fr eq uency to 500kH z. Fl oat OS C to set the fr eq uency to 750kH z.
11 PWMI
PWM Signal Input. This PWM signal is used for brightness control in PWM mode or DPST mode. This signal
is filtered 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
filter with an internal 40kΩ (typ) resistor to filter the PWM signal into an analog signal whose level represents
the duty-cycle information of the input PWM signal.
13 FSET
D P W M Fr eq uency Ad j ustm ent P i n. C onnect a r esi stor fr om FS E T to GN D to set the i nter nal D P WM fr eq uency:
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.
fR
DPWM =×+
109
αγ[]Ω
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
______________________________________________________________________________________ 11
Pin Description (continued)
PIN NAME FUNCTION
22 VDD Boost Reg ul ator M OS FE T G ate D r i ve S up p l y. Byp ass V
D D
to G N D w i th a cer am i c cap aci tor of 1µF or g r eater .
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 sufficient copper connection to ensure
low thermal resistance. See the PCB Layout Guidelines section.
Detailed Description
The MAX17061 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,
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 head-
room for the current sources to regulate their respec-
tive string currents. The MAX17061 features selectable
switching frequency (500kHz, 750kHz, or 1MHz), which
allows trade-offs between external component size and
operating efficiency. The control architecture automati-
cally 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 bright-
ness 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 com-
mand 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 current-
limit condition, the controller shuts down after a 128µs
overcurrent fault timer expires. A thermal-shutdown cir-
cuit provides another level of protection.
MAX17061
The MAX17061 includes a 5V linear regulator that pro-
vides 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, connect the IN pin to an input greater than 5.5V.
Fixed-Frequency Step-Up Controller
The MAX17061’s fixed-frequency, current-mode, step-
up controller automatically chooses the lowest active
FB_ voltage to regulate the output voltage. Specifically,
the difference 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 cur-
rent to the CCV output to deliver the required peak-
inductor 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 induc-
tor 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 lin-
ear 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).
8-String White LED Driver with
SMBus for LCD Panel Applications
12 ______________________________________________________________________________________
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
Figure 1. Typical Operating Circuit
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
______________________________________________________________________________________ 13
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
Figure 2. Control Circuit Block Diagram
MAX17061
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 approx-
imately 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 dis-
charged down to 5.6V (typ) and then continuously dis-
charged 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 inter-
nal 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 disabled. 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 clear-
ing 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 regulator remains on, providing a 4.35V
(typ) output voltage to VCC, with 1µA current-sourcing
capability. The fault/status register is not reset in shut-
down. 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.
8-String White LED Driver with
SMBus for LCD Panel Applications
14 ______________________________________________________________________________________
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
Figure 3. Low-Input-Voltage Application Circuit
Frequency Selection
A tri-level OSC input sets the internal oscillator frequen-
cy for step-up converter, as shown in Table 1. High-fre-
quency (1MHz) operation optimizes the regulator for
the smallest component size, at the expense of efficien-
cy 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 rea-
son, the MAX17061 features a dedicated overvoltage
feedback 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 comparator turns off the internal power MOS-
FET. This step-up converter switch is reenabled after
the VOV drops 60mV (typ) hysteresis below the protec-
tion threshold. This overvoltage-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
current sources. These specialized current sources are
accurate to within ±1.5% between strings and can be
switched on and off within 15µs, enabling PWM fre-
quencies 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 full-
scale 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
maintaining 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
powered 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 corre-
sponding 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 converter’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/status resister are set (see the
Fault/Status
Register
section).
Open-Current Source Protection
The MAX17061 step-up converter output voltage is reg-
ulated 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 disabled. The controller allows the unaf-
fected LED strings to operate normally. The LED short-
protection feature is disabled 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
resistor and has 1.5% accuracy for RFSET = 464kΩ. The
duty cycle of this DPWM signal can be controlled exter-
nally 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 controls 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 modu-
lated in a consistent flicker-free manner.
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
______________________________________________________________________________________ 15
Table 1. Frequency Selection
OSC PIN CONNECTION SWITCHING FREQUENCY (kHz)
GND 500
Open 750
VCC 1000
MAX17061
Full-Scale LED Brightness
in DPWM Dimming Control
The full-scale LED current in the DPWM dimming is
determined by resistance from the ISET pin to ground:
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:
where: α= 10.638
γ= 58509
The adjustable range for the FSET resistor, RFSET, is
from 42kΩto 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 com-
mand value. This DPWM control provides a dimming
range with 8-bit resolution down to 2.7% and supports
Intel DPST to maximize battery life.
fR
DPWM =×+
109
αγ[]Ω
ImA k
R
LEDMAX ISET
=×20 200 Ω
8-String White LED Driver with
SMBus for LCD Panel Applications
16 ______________________________________________________________________________________
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
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
Figure 4. LED Current Control by DPWM Signal in Dimming
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 without 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 oper-
ating 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 inter-
preted. 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 out-
put brightness. In DPST mode, the overall brightness
level is the normalized product of the SMBus command
setting and PWM input duty cycle. The PWM signal
starts from 100% when operating in DPST mode.
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
______________________________________________________________________________________ 17
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 FIELD DEFINITION DESCRIPTION
Bit [7..0] BRT [7..0] 8-bit brightness setting, adjusting brightness levels in 256 steps, default value is 0xFF.
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 reg-
ister 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.
Bit field definitions:
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 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
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.
Bit field definitions:
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
18 ______________________________________________________________________________________
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 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 faul t excep t LE D op en/shor t occur s ( l og i c O R of al l faul t cond i ti ons, 1 = faul t cond i ti on, 0 = no faul t)
Fault/Status Register: Address is 0x02. This register has 6 status bits that allow monitoring the backlight con-
troller’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.
Bit field definitions:
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 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
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.
Bit field definitions:
Table 2. Operating Modes Selected by Device Control Register Bits 1 and 2
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
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 controller and current sources shut down and do
not restart until the die temperature drops by 15°C.
When thermal shutdown occurs, Bit 1 of fault/status
register is set to 1.
Design Procedure
All MAX17061 designs should be prototyped and test-
ed prior to production. Table 4 provides a list of power
components 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 output
capacitor. The output current for the converter SKIP oper-
ation can be calculated by the following equation:
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.
IVT f
LV V V
O SKIP IN ON MIN OSC
OUT DIODE IN
() ()
<××
×× + −
()
22
2
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
______________________________________________________________________________________ 19
Table 3. Vendor IDs
ID VENDOR
0 Maxim
1 Micro Semi
2MPS
3 O2 Micro
4TI
5ST
6 Analog Devices
7–14 Reserved
15 Vendor ID register not implemented
Table 4. Component List
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 Rectifier 0.7A, 60V Schottky diode (US-flat)
Toshiba CUS04
3A, 60V Schottky diode
Nihon EC31QS06
Table 5. Component Suppliers
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
To ensure the stable operation, the MAX17061 includes
slope compensation, which sets the minimum inductor
value. In continuous-conduction mode (CCM), the mini-
mum inductor value is calculated with the following
equation:
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
internal current-sense circuit.
The controller can also operate in discontinuous con-
duction 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:
where the LDCM(MAX) is the maximum inductor value
for DCM, ηis 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 fre-
quency, and inductor value. Because the slope com-
pensation is used to stabilize the feedback loop, the
inductor current limit depends on the duty cycle, and is
determined with the following equation:
where 24.7mV is the scale factor from the slope com-
pensation, 1.9A is a typical current limit at 75% duty
cycle, and D is the duty cycle.
The output current capability depends on the current-
limit value and operating mode. The maximum output
current in CCM is governed by the following equation:
where ILIM is the current limit calculated above, ηis the
nominal regulator efficiency (85%), and D is the duty
cycle. The corresponding duty cycle for this current is:
where VDIODE is the forward voltage of the rectifier
diode and RON is the internal MOSFET’s on-resistance
(0.15Ωtyp).
The maximum output current in DCM is governed by
the following equation:
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 operating
mode, efficiency, maximum output load capability, tran-
sient 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 rip-
ple, 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 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
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, inde-
pendent of the internal slope compensation mode, but
there is a maximum inductor value requirement to
ensure the DCM operating mode.
ILI f
VV V
OUT DCM MAX LIM OSC
OUT DIODE IN
_()
=×××
×+ −
()
2
2
η
DVVV
VIRV
OUT IN DIODE
OUT LIM ON DIODE
=−+
−× +
II
DV
fL
OUT CCM MAX LIM IN
OSC
_()
.
=−
××
×
⎛
⎝
⎜⎞
⎠
⎟
05
IA
mV D
R
LIM S
=+ ×−
()
19 24 7 0 75
...
LDCM V
VV
V
fVI
MAX IN MIN
OUT MAX DIODE
IN MIN
OSC MAX OUT MAX OUT MAX
() ()
()
()
() () ()
=− +
⎛
⎝
⎜⎞
⎠
⎟
××
×× ×
1
2
2η
LVVVR
mV f
CCM MIN
OUT MAX DIODE IN MIN S
OSC MIN
()
() ()
()
.
=+−×
()
×
××
2
2247
8-String White LED Driver with
SMBus for LCD Panel Applications
20 ______________________________________________________________________________________
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 cur-
rent. 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 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 val-
ues 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:
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:
where 24.7mV is a scale factor from slope compensa-
tion, and the RSis the equivalent current-sensing scale
factor (12mΩtyp):
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 appropri-
ate curve in the
Typical Operating Characteristics
:
2) Calculate the ripple current at that operating point
and the peak current required for the inductor:
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:
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 0.1Ωseries 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:
In CCM, the inductor has to be higher than LCCM(MIN):
A10µH inductor is chosen, which is higher than the
minimum L that guarantees stability in CCM.
LVV Vm
mV MHz H
CCM MIN()
..
.. .=+−×
()
×
×× =
35 9 0 4 2 7 12
2247 09 60
Ωμ
LV
V
VV
mA MHz H=⎛
⎝
⎜⎞
⎠
⎟−
×
⎛
⎝
⎜⎞
⎠
⎟⎛
⎝
⎜⎞
⎠
⎟=
7
35 9
35 9 7
100 1
085
1944
2
.
..
.μ
II I
PEAK IN DCMAX RIPPLE
=+
(, ) 2
LV
VV
V
fVI
DCM MAX IN MIN
OUT MAX DIODE
IN MIN
OSC MAX OUT MAX OUT MAX
() ()
()
()
() () ()
=− +
⎛
⎝
⎜⎞
⎠
⎟
××
×× ×
1
2
2η
IVV V
LV f
RIPPLE
IN MIN OUT MAX IN MIN
OUT MAX OSC
=×−
()
××
() ( ) ()
()
IIV
V
IN DCMAX OUT MAX OUT
IN MIN MIN
(, ) ()
()
=×
×η
LVVVR
mV f
CCM MIN
OUT MAX DIODE IN MIN S
OSC MIN
()
() ()
()
.
=+−×
()
×
××
2
2247
LV
V
VV
I f LIR
IN MIN
OUT
OUT IN MIN
OUT MAX OSC
TYP
=⎛
⎝
⎜⎞
⎠
⎟−
×
⎛
⎝
⎜⎞
⎠
⎟⎛
⎝
⎜⎞
⎠
⎟
__
()
2η
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
______________________________________________________________________________________ 21
MAX17061
The peak-inductor current at minimum input voltage is
calculated as follows:
Alternatively, choosing a DCM operating mode at 750kHz
and estimating efficiency of 85% at this operating point:
A 4.7µH inductor is chosen. The peak inductor current
at minimum input voltage is calculated as follows:
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):
and:
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
voltage biasing. Ensure the selected capacitor has
enough capacitance at actual DC biasing.
Rectifier Diode Selection
The MAX17061’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommend-
ed 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:
In Figure 1, the output OVP voltage is set to:
Input Capacitor Selection
The input capacitor (CIN) filters the current peaks
drawn from the input supply and reduces noise injec-
tion 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 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 val-
ues 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 low-
pass filter.
VV
M
kV
OUT OVP()
.(
.
.)=×+ ≈1 236 1 221
61 9 45
Ω
Ω
VV R
R
OUT OVP OV TH() _
=×+
⎛
⎝
⎜⎞
⎠
⎟
11
2
VIR
RIPPLE ESR PEAK ESR COUT() ( )
≈
VI
C
VV
Vf
RIPPLE C OUT MAX
OUT
OUT MAX IN MIN
OUT MAX OSC
() () () ()
()
≈−
⎛
⎝
⎜⎞
⎠
⎟
VV V
RIPPLE RIPPLE C RIPPLE ESR
=+
() ( )
ImA V V V V
uH MHz V V A
PEAK =×× × + −
()
×××+
()
=
100 2 35 9 35 9 0 4 7
47 0675 085 359 04 147
...
.. . ...
LV
VV
V
MHz V mA H
DCM MAX() ..
() .
.. .
=− +
⎛
⎝
⎜⎞
⎠
⎟
××
×××
=
17
35 9 0 4
7085
2 0 825 35 9 100 56
2μ
ImA V
V
VVV
H V MHz A
PEAK =×
×
+×−
()
×× × =
100 35 9
7085
73597
210 359 09 092
.
.
.
.. .
μ
8-String White LED Driver with
SMBus for LCD Panel Applications
22 ______________________________________________________________________________________
LED Selection and Bias
The series/parallel configuration of the LED load and the
full-scale bias current have a significant effect or regula-
tor performance. LED characteristics vary significantly
from manufacturer to manufacturer. Consult the respec-
tive LED data sheets to determine the range of output
voltages for a given brightness and LED current. In gen-
eral, 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 spec-
trum. A blue bias is often acceptable for business appli-
cations but not for high-image-quality applications such
as DVD players. Direct DPWM dimming is a viable solu-
tion 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 num-
ber 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.
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 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 4.8V (typ). Otherwise, the internal LED short-
protection 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
output 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 capac-
itor 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,
then to the input capacitor’s negative terminal. The
high-current output loop is from the positive termi-
nal of the input capacitor to the inductor, to the rec-
tifier diode, 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 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 power-
ground traces improves efficiency and reduces out-
put-voltage ripple and noise spikes. Create an
analog ground island (AGND) consisting of the
overvoltage detection divider ground connection,
the ISET and FSET resistor connections, 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.
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
______________________________________________________________________________________ 23
MAX17061
4) Place the overvoltage detection divider resistors as
close as possible to the OV pin. The divider’s cen-
ter 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 run-
ning 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.
8-String White LED Driver with
SMBus for LCD Panel Applications
24 ______________________________________________________________________________________
Chip Information
TRANSISTOR COUNT: 21,800
PROCESS: BiCMOS
26
27
25
24
10
9
11
FB4
N.C.
FB5
N.C.
FB6
12
FB3
PGND1
N.C.
LX1
IN
LX2
SCL
12
OV
4567
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
Pin Configuration
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
______________________________________________________________________________________ 25
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)
24L QFN THIN.EPS
MAX17061
8-String White LED Driver with
SMBus for LCD Panel Applications
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.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________
26
© 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information
go to www.maxim-ic.com/packages.)