General Description
The MAX17061A is a high-efficiency driver for white
lightemitting 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 MAX17061A has a wide input
voltage range from 7.5V to 26V, and provides a fixed
25mA or adjustable 15mA to 30mA full-scale LED current.
The MAX17061A internally generates a DPWM signal for
accurate WLED dimming control. The DPWM frequency
is resistor programmable, while DPWM duty cycle is co
trolled directly from an external PWM signal or through a
control word through the MAX17061A’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 MAX17061A 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
MAX17061A also features short LED detection. 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 MAX17061A 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 MAX17061A’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 MAX17061A fea-
tures selectable switching frequency (500kHz, 750kHz, or
1MHz), which enables a wide variety of applications that
can trade off component size for operating frequency.
The MAX17061A is available in a thermally enhanced
28-pin, 4mm x 4mm Thin QFN package.
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
Applications
● Notebook, Subnotebook, and Tablet Computer
Displays
●Handy Terminals
SMBus is a trademark of Intel Corp.
FB1
CCV
PGND1, 2
IN
VIN
LX1, 2
OV
FB2
FB3
FB4
FB5
FB6
FB7
FB8
L1 D1
VDD
ISET
FSET
VCC
VCC
5V
PWMIPWM
R1
R2
MAX17061A
VOUT
SCLCLK
SDADATA
OSCN.C.
GND
PWMO
EP
Ordering Information and Pin Description appear at end of
data sheet.
MAX17061A 8-String White LED Driver with
SMBus for LCD Panel Applications
19-4485; Rev 1; 11/14
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 = 5V, 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 7.5 26 V
IN UVLO Threshold Rising edge 7.08 7.2 7.32 V
Falling edge 6.86 6.98 7.1
IN Input Current VIN = 26V MAX17061A is enabled 70 110 µA
MAX17061A is disabled, TA = +25°C +1 +1
VCC Input Voltage 4.5 5 5.5 V
VCC UVLO Threshold Rising edge, typical hysteresis = 10mV 4.00 4.25 4.45 V
VCC Quiescent Current MAX17061A is enabled 1.24 2 mA
VCC Shutdown Current MAX17061A is disabled 10 µA
BOOST CONVERTER
LX On-Resistance 20mA from LX_ to PGND 0.15 0.3 Ω
LX Leakage Current 45V on LX_, TA = +25°C 1 µA
Operating Frequency
VOSC = VCC 0.9 1.0 1.1 MHz
VOSC = open 675 750 825 kHz
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 %
Maximum Duty Cycle 94 95.5 97 %
LX Current Limit Duty cycle = 75% (Note 1) 1.6 A
CONTRL INPUT
SDA, SCL Logic Input High Level 2.1
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
MAX17061A 8-String White LED Driver with
SMBus for LCD Panel Applications
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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 = 5V, 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 TA = +25°C -0.3 +0.3 µA
ISET, FSET Leakage Current ISET, FSET to VCC, TA = +25°C +1 µA
OV Leakage Current TA = +25°C -0.1 +0.1 µA
SDA, SCL Input Bias Current TA = +25°C -1 +1 µA
SDA Output Low Sink Current VSDA = 0.4V 4 mA
OSC Leakage Current TA = +25°C 3 +3 µA
LED CURRENT
Full-Scale FB_ Output Current
ISET = VCC 24.5 25.0 25.5
mA
RISET = 133kΩ28.8 30.0 31.2
RISET = 200kΩ19.3 20.0 20.7
RISET = 266kΩ14.4 15.0 15.6
ISET High-Level Threshold Default setting VCC - 0.4 V
ISET Output Voltage 1.166, 1.236 1.306 V
Current Regulation
Between Strings ISET = VCC -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, OSC = VCC) (Note 1) 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 5.2 5.6 6.0 V
FB_ Undervoltage Threshold 130 175 220 mV
Boost Global Fail 48 84 120 mV
Thermal-Shutdown Threshold (Note 1) 160 °C
Overcurrent Fault
Shutdown Timer IPEAK > 3.3A at duty = 0% or 1.8A at duty = 90% (typ) 88 128 168 µs
FB_ Overvoltage-Fault Timer 1.7 2 2.3 ms
MAX17061A 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 = 5V, 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, 5V = RFSET = 464kΩ, VPWMI = GND,
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
IN Input Voltage Range 7.5 26 V
IN UVLO Threshold Rising edge 7.08 7.32 V
Falling edge 6.86 7.1
IN Input Current VIN = 26V MAX17061A is enabled 110 µA
VCC Input Voltage 4.5 5.5 V
VCC UVLO Threshold Rising edge, typical hysteresis = 10mV 4.00 4.45 V
VCC Quiescent Current MAX17061A is enabled 2 mA
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 µs
SDA Setup Time from SCL TSU:DAT 250 µs
SCL Low Period TLOW 4.7 µs
SCL High Period THIGH 4µs
MAX17061A 8-String White LED Driver with
SMBus for LCD Panel Applications
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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, 5V = RFSET = 464kΩ, VPWMI = GND,
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETER CONDITIONS MIN TYP MAX UNITS
VCC Shutdown Current MAX17061A is disabled 10 µA
BOOST CONVERTER
LX On-Resistance 20mA from LX_ to PGND 0.3 Ω
Operating Frequency
VOSC = VCC 0.89 1.10 MHz
VOSC = open 675 825 kHz
VOSC = GND 450 560
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 94 %
LX Current Limit Duty cycle = 75% (Note 1) 1.6 A
CONTRL INPUT
SDA, SCL Logic Input High Level 2.1
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
SDA Output Low Sink Current VSDA = 0.4V 4 mA
LED CURRENT
Full-Scale FB_ Output Current
ISET = VCC 24.5 25.5
mA
RISET = 133kΩ28.6 31.4
RISET = 200kΩ19.0 21.0
RISET = 266kΩ14.4 15.6
ISET High-Level Threshold Default setting VCC - 0.4 V
ISET Output Voltage 1.166 1.306 V
Current Regulation
Between Strings ISET = VCC -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, OSC = VCC) (Note 1) 200 mVP-P
FB_ On-Resistance VFB_ = 50mV (includes 10Ω sense resistor) 28.4 Ω
MAX17061A 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, 5V = RFSET = 464kΩ, VPWMI = GND,
TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
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
Boost Global Fail 48 120 mV
Overcurrent FAULT
Shutdown Timer IPEAK > 3.3A at duty = 0% or 1.8A at duty = 90% (typical) 88 168 µs
FB_ Overvoltage Fault Timer 1.6 2.4 ms
PWM FILTER
PWM Output Impedance 20 60 kΩ
DPWM Oscillator Frequency
RFSET = 464kΩ 197 203 Hz
RFSET = 113kΩ 750 820
RFSET = 65kΩ 1.27 1.40 kHz
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 µs
SDA Setup Time from SCL TSU:DAT 250 µs
SCL Low Period TLOW 4.7 µs
SCL High Period THIGH 4µs
MAX17061A 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,
LEDs = 10 series x 4 parallel strings, TA = +25°C, unless otherwise noted.)
LED CURRENT
vs. SMBus BRIGHTNESS SETTING
MAX17061A toc02
SMBus BRIGHTNESS SETTING
LED CURRENT (mA)
200 250150100500
10
15
20
25
30
0
5
LED CURRENT
vs. PWMI DUTY CYCLE
MAX17061A 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%)
MAX17061A 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
MAX17061A toc05
LED CURRENT (mA)
17 2014118
10
15
20
25
30
0
5
5
SMBus = 0xFF
SMBus = 0x1F
INPUT VOLTAGE (V)
VCC SUPPLY CURRENT
vs. INPUT VOLTAGE
MAX17061A toc06
SUPPLY CURRENT (mA)
25201510
2
3
4
5
0
1
5
INPUT VOLTAGE (V)
SMBus = 255
SMBus = 0
VCC SHUTDOWN CURRENT
vs. INPUT VOLTAGE
MAX17061A toc07
SHUTDOWN CURRENT (A)
25201510
5.88
5.90
5.92
5.94
5.98
5.96
6.00
5.80
5.84
5.82
5.86
5
INPUT VOLTAGE (V)
BOOST CONVERTER EFFICIENCY vs.
INPUT VOLTAGE (BRIGHTNESS = 100%)
MAX17061A toc01
INPUT VOLTAGE (V)
BOOST CONVERTER EFFICIENCY (%)
25201510
91
92
93
94
95
96
90
5
MAX17061A 8-String White LED Driver with
SMBus for LCD Panel Applications
Maxim Integrated
│
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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.)
STARTUP WAVEFORMS
(BRIGHTNESS = 100%)
MAX17061A toc10
400s/div
VLX
20V/div
IL
1A/div
VOUT
20V/div
VCCV
2V/div
0V
0V
0V
0A
SWITCHING WAVEFORMS
(VIN = 7V, BRIGHTNESS = 100%)
MAX17061A toc08
1s/div
VLX
20V/div
IL
200mA/div
0V
0mA
STARTUP WAVEFORMS
(SMBus = 0x04)
MAX17061A toc11
400s/div
VLX
20V/div
IL
1A/div
VOUT
20V/div
VCCV
2V/div
0V
0V
0V
0A
SWITCHING WAVEFORMS
(VIN = 20V, BRIGHTNESS = 100%)
MAX17061A toc09
1s/div
VLX
20V/div
IL
200mA/div
0V
0mA
LED CURRENT WAVEFORMS
(SMBus = 0x80)
MAX17061A toc12
2ms/div
VFB1
10V/div
IL
500mA/div
ILED
20mA/div
VOUT
20V/div
0V
0mA
0mA
0V
LED CURRENT WAVEFORMS
(SMBus = 0x04)
MAX17061A toc13
2ms/div
VFB1
10V/div
IL
500mA/div
ILED
20mA/div
VOUT
20V/div
0V
0mA
0mA
0V
MAX17061A 8-String White LED Driver with
SMBus for LCD Panel Applications
Maxim Integrated
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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.)
LINE TRANSIENT RESPONSE
(VIN = 12V→19V, BRIGHTNESS = 100%)
MAX17061A toc16
100s/div
VOUT
20V/div
IL
1A/div
IFB1
20mA/div
VIN
10V/div
0V
0V
0A
0mA
LED-OPEN FAULT PROTECTION
(BRIGHTNESS = 100%, LED OPEN ON FB1)
MAX17061A toc14
400s/div
VFB1
1V/div
IFB2
20mA/div
IFB2
10V/div
VOUT
20V/div
0V
0V
0V
0mA
LINE TRANSIENT RESPONSE
(VIN = 19V→12V, BRIGHTNESS = 100%)
MAX17061A toc17
100s/div
VOUT
20V/div
IL
1A/div
IFB1
20mA/div
VIN
10V/div
0V
0V
0A
0mA
LED-SHORT FAULT PROTECTION
(BRT = 100%, 2 LEDs SHORT ON FB1)
MAX17061A toc15
1ms/div
VFB1
5V/div
VFB2
10V/div
IFB2
20mA/div
IFB1
20mA/div
0V
0V
0mA
0mA
LED CURRENT BALANCE
vs. INPUT VOLTAGE
MAX17061A toc18
LED CURRENT BALANCE (%)
17 2014118
0.10
0.15
0.20
0.25
0.30
0
0.05
5
INPUT VOLTAGE (V)
MAX17061A 8-String White LED Driver with
SMBus for LCD Panel Applications
Maxim Integrated
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Typical Operating Characteristics (continued)
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, 7.5V to 26V. Bypass IN to GND directly at the pin with a 0.1μF or greater ceramic capacitor.
When IN voltage is below its UVLO threshold, the MAX17061A turns off the output.
9
DPWM
10
fR[ ]
=α× Ω +γ
MAX17061A 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 MAX17061A is a high-efficiency driver for arrays
of white LEDs. It contains a fixed-frequency current-
mode PWM step-up controller, 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 MAX17061A features select-
able switching frequency (500kHz, 750kHz, or 1MHz),
which allows trade-offs between external component size
and operating efficiency.
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 MAX17061A has multiple features to protect the con-
troller from fault conditions. Separate feedback loops limit
the output voltage in all circumstances. The MAX17061A
checks each FB_ voltage during the operation. If one or
more strings are open, the corresponding FB_ voltages
are pulled below 175mV (typ), and opencircuit 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 circuit
provides another level of protection.
The MAX17061A requires an external 5V supply to provide
the internal bias and gate drive for the step-up controller.
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 Control Supply Input. VCC provides power to the MAX17061A. Bypass VCC to GND with a ceramic
capacitor of 1μF or greater.
24 CCV Step-Up Converter Compensation Pin. Connect a 0.022μF ceramic capacitor and 5.1kΩ resistor from CCV
to GND. When the MAX17061A 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.
MAX17061A 8-String White LED Driver with
SMBus for LCD Panel Applications
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Pin Description (continued)
Fixed-Frequency Step-Up Controller
The MAX17061A’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 current
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.
At high input voltages when the on-time is pushed to be
lower than the minimum on-time (90ns typ), the boost
converter runs with minimum on-time, boosting the output
voltage higher than the input voltage.
5V Supply VCC and UVLO
The MAX17061A requires an external 5V VCC supply for
internal control voltage.
The MAX17061A 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
approximately 85mV.
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
MAX17061A
VOUT
UP TO 45V
220pF
464kΩ
+5V
VCC
0.022µF
5.1kΩ
CCV
SCLCLK
SDADATA
PWMO
EP
R2
61.9kΩ
2µF
R1
2.21MΩ
MAX17061A 8-String White LED Driver with
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Figure 2. Control Circuit Block Diagram
IN UVLO
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
MAX17061A
0x02 0x01 0x00
MUX
PWM_SEL
PWM_MD
DIMMING
BLOCK DIAGRAM
MAX17061A 8-String White LED Driver with
SMBus for LCD Panel Applications
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The VCC and VDD pins should be bypassed to GND with
a minimum 1μF ceramic capacitor.
IN UVLO
The MAX17061A implements an IN UVLO function to
safeguard the operation in the specified range. When
IN pin voltage drops below its UVLO threshold (6.98V
typ), the converter is shut off and the BL_Stat bit of the
fault/status register is cleared. The BL_CTL bit of control
register is not altered. When IN pin voltage rises above
the UVLO rising edge threshold (7.2V typ) the backlight
resumes automatically if the BL_CTL bit is set to 1.
Startup
At startup, the MAX17061A 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 MAX17061A 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
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 MAX17061A 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. The
fault/status register is set accordingly in shutdown. When
bit 0 of the device control register (0x01) is recycled to
1, the MAX17061A exits shutdown mode and starts. The
fault/status register is reset at startup.
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
smallest 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
MAX17061A 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 MOSFET. This step-up converter switch
is reenabled after the VOV drops 60mV (typ) hysteresis
below the protection 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
capability are critical for LCD backlight applications. The
MAX17061A 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
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 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 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
converter’s error amplifier and is used to set the output
voltage.
Table 1. Frequency Selection
OSC PIN
CONNECTION
SWITCHING FREQUENCY
(kHz)
GND 500
Open 750
VCC 1000
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Current-Source Fault Protection
The MAX17061A 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, as
well as bit 0 of the fault/status resister are set (see the
Fault/Status Register section).
Open-Current Source Protection
The MAX17061A 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
normally. If all strings in use are open, the MAX17061A
shuts down the step-up converter.
The MAX17061A 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 unaffected LED strings to operate
normally. When only one string is in operation and there
are shorts on some LEDs, then the converter does not shut
down. Instead, the output voltage is adjusted accordingly.
The LED short-protection feature is disabled during the
soft-start phase of the step-up converter.
Dimming Control
The MAX17061A 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 externally through
two interfaces: PWM and SMBus. The ISET pin sets
the amplitude of the current sources for each LED string
(Figure 3). 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 modulated in a consistent flicker-free
manner.
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:
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.
Figure 3. LED Current Control by DPWM Signal in Dimming
D = 30% D = 12.5% D = 6.25%
DPWM
0A
ILEDMAX
ILED
D = 50%
D = tON
tON
tDPWM
tDPWM
DPWM DIMMING MODE
MAX17061A 8-String White LED Driver with
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DPWM Frequency Setting
The MAX17061A 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 frequency of
200Hz to 2kHz.
Dimming Control Interfaces
The MAX17061A’s dimming control circuit consists of two
interfaces: PWM and SMBus. The block diagram of these
two input interfaces is shown in Figure 4. 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 a 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.
The SMBus interface can be used to adjust the
dimming, as well as shut down the MAX17061A. Before
the MAX17061A 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. Even in
PWM dimming mode, only the PWMI interface is used for
brightness control; the MAX17061A cannot run without the
SMBus interface. For sister products without the SMBus
interface, contact Maxim Integrated Products, Inc.
Dimming Control Register Descriptions
The MAX17061A includes four registers to monitor
and control brightness, fault status, identification, and
operating mode. The slave address is 0b0101100. The
MAX17061A uses two multiplexers internally to direct
the dimming signal processing (Figure 4). These two
multiplexers are controlled by 2 bits of the device control
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
controlled 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 normalized product of the SMBus command setting
and PWM input duty cycle. The PWM signal starts from
100% when operating in DPST mode.
Figure 4. LED Current Control by DPWM Signal in Dimming
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
MAX17061A
FAULT/STATUS
REGISTER
DEVICE
CONTROL
REGISTER
BRIGHTNESS
CONTROL
REGISTER
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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.
Table 2. Operating Modes Selected by Device Control Register Bits 1 and 2
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 are 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 control (1 = on, 0 = off), 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
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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 including 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. The value
for the MAX17061A is 0x81.
The list of ID values for vendors is shown in Table 3.
Thermal Shutdown
The MAX17061A 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 0 and Bit 1 of fault/status
register is set to 1.
Table 3. Vendor IDs
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 At least 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, logic OR of all fault conditions (1 = fault condition, 0 = no fault)
REGISTER 0x03 ID REGISTER DEFAULT VALUE 0x81
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 = 1
ID VENDOR
0 Maxim
1 Micro Semi
2 MPS
3 O2 Micro
4TI
5 ST
6 Analog Devices
7-14 Reserved
15 Vendor ID register not implemented
MAX17061A 8-String White LED Driver with
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Design Procedure
All MAX17061A designs should be prototyped and tested
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
To ensure the stable operation, the MAX17061A includes
slope compensation, which sets the minimum inductor
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
L2 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
internal current-sense circuit.
The controller can also operate in discontinuous
conduction mode (DCM). In this mode, the inductor value
can be lower, but the peak inductor current is higher than
in CCM. In DCM, the maximum inductor value is calculated
with the following equation:
= −
+
×η
××× ×
IN(MIN)
DCM(MAX) OUT(MAX) DIODE
2
IN(MIN)
OSC(MAX) OUT(MAX) OUT(MAX)
V
L1
VV
V
2f V I
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.
Table 4. Component List
Table 5. Component Suppliers
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 Electronics North America, Inc. 770-436-1300 www.murata-northamerica.com
Nichia Corp. 248-352-6575 www.nichia.com
Sumida Corp. 847-545-6700 www.sumida.com
Toshiba America Electronic Components, Inc. 949-455-2000 www.toshiba.com/taec
Vishay 203-268-6261 www.vishay.com
MAX17061A 8-String White LED Driver with
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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
0.5 D V
II
fL
××
= −
×
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 MAX17061A
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.
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 current
(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
=
×
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The MAX17061A 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
IN(DC,MAX) 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 fo
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 Figure 1. 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 9.44µH
35.9V 100mA 1MHz 1
−
= =
×
In CCM, the inductor has to be higher than LCCM(MIN):
( )
CCM(MIN) 35.9V 0.4V 2 7V 12m
L 6.0µH
2 24.7mV 0.9MHz
+ −× × Ω
= =
××
A10μH inductor is chosen, which is higher than the mini-
mum L that guarantees stability in CCM.
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 10µH 35.9V 0.9MHz
×
=×
×−
+=
×× ×
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
5.6µH
2 0.825MHz 35.9V 100mA
= −
+
×
×=
× ××
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
IVV
VC Vf
= +
−
≈
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and:
VRIPPLE(ESR) ≈ IPEAKRESR(COUT)
where IPEAK is the peak inductor current (see the Inductor
Selection section).
The output voltage ripple should be low enough for the
FB_ current-source regulation. The ripple voltage should
be less than 200mVP-P. For ceramic capacitors, the 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 MAX17061A’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 Figure 1.
Typical Operating Circuit (Figure 1) because of the high
source impedance seen in typical lab setups. Actual appli-
cations 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 Figure 1. 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.
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 MAX17061A 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.
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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
MAX17061A 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.
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. Avoidrunning 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 MAX17061A evaluation kit for an example of
proper board layout.
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+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
28 TQFN-EP T-2844+1 21-0139 90-0035
PART TEMP RANGE PIN-PACKAGE
MAX17061AETI+ -40°C to +85°C 28 TQFN-EP*
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
MAX17061A
GND PGND2
3
18
28 8
FB2 FB7
CCV
23 13 FSET
VCC
22 14 SDA
VDD
TOP VIEW
TQFN-EP
4mm x 4mm
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Chip Information
PROCESS: BiCMOS
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.
Pin Conguration
Ordering Information
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.
MAX17061A 8-String White LED Driver with
SMBus for LCD Panel Applications
© 2014 Maxim Integrated Products, Inc.
│
25
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
02/09 Initial release —
111/14 No /V OPNs; deleted “Automotive Systems” from Applications section; moved
Ordering Information to end of data sheet; updated Package Information 1, 24
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.
