Rainbow Electronics MAX17061 User Manual

General Description

The MAX17061 is a high-efficiency driver for white light­emitting diodes (LEDs). It is designed for large liquid­crystal displays (LCDs) that employ an array of LEDs as
the light source. An internal switch current-mode step-up
controller drives the LED array, which can be configured
for up to eight strings in parallel and 10 LEDs per string.
Each string is terminated with ballast that achieves ±1.5%
current-regulation accuracy between strings, ensuring
even LED brightness. The MAX17061 has a wide input­voltage range from 4.5V to 26V, and provides a fixed
25mA or adjustable 15mA to 30mA full-scale LED current.

The MAX17061 internally generates a DPWM signal for
accurate WLED dimming control. The DPWM frequency
is resistor programmable, while DPWM duty cycle is con­trolled directly from an external PWM signal or through a
control word through the MAX17061’s SMBus™ inter­face. This DPWM control provides a dimming range with
8-bit resolution and supports Intel display-power-saving
technology (DPST) to maximize battery life.

The MAX17061 has multiple features to protect the con­troller from fault conditions. Separate feedback loops
limit the output voltage under any circumstance, ensur­ing safe operation. Once an open string is detected,
the string is disabled while other strings operate nor­mally. The MAX17061 also features short LED detec­tion. The shorted strings are also disabled after a 2ms
fault blanking interval. The controller features cycle-by­cycle current limit to provide stable operation and soft­start capability. If the MAX17061 is in current-limit
condition, the step-up converter is latched off after an
internal timer expires. A thermal-shutdown circuit pro­vides another level of protection.

The MAX17061’s step-up controller features an internal
150mΩ (typ), 45V (max) power MOSFET with local cur­rent-sense amplifier for accurate cycle-by-cycle current
limit. This architecture greatly simplifies the external cir­cuitry and saves PCB space. Low-feedback voltage at
each LED string 625mV (typ) at 25mA LED current helps
reduce power loss and improve efficiency. The
MAX17061 features selectable switching frequency
(500kHz, 750kHz, or 1MHz), which enables a wide vari­ety of applications that can trade off component size for
operating frequency.

The MAX17061 is available in a thermally enhanced
28-pin, 4mm x 4mm Thin QFN package.

Applications

Features

o Accurate Dimming Control Using SMBus, PWM

Interface

o Dimming Range with 8-Bit Resolution
o Adjustable DPWM Frequency with 1.5% Accuracy
o Up to Eight Parallel Strings Multiple Series-

Connected LEDs

o ±1.5% Current Regulation Accuracy Between

Strings

o Low String Feedback Voltage: 625mV at 25mA

LED Current

o Full-Scale LED Current Adjustable from 15mA to

30mA, or Preset 25mA

o Open and Short LED Protections
o Output Overvoltage Protection
o 0.15Ω Internal HV Power MOSFET (45V max)
o Wide Input-Voltage Range from 4.5V to 26V
o 500kHz/750kHz/1MHz Selectable Switching

Frequency

o Small 28-Pin, 4mm x 4mm, Thin QFN package

MAX17061

8-String White LED Driver with

SMBus for LCD Panel Applications

________________________________________________________________

Maxim Integrated Products

1

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

PIN-PACKAGE

MAX17061ETI+

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

TEMP RANGE

-40oC to +85oC

L1

LX1, 2

PGND1, 2

D1

R1

OV

R2

FB1
FB2
FB3
FB4
FB5
FB6

FB7

FB8

V

IN

IN

V

DD

V

CC

ISET

CCV

MAX17061

PWMIPWM
PWMO

GND

OSCN.C.

SCLCLK

SDADATA

FSET

EP

V

OUT

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VIN= 12V, C

CCV

= 0.022µF, R

CCV

= 5.1kΩ, V

ISET

= V

OSC

= VDD= VCC, R

FSET

= 464kΩ, V

PWMI

= GND,

T

A

= 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

V

CC

, VDD, PWMI, SDA, SCL to GND........................-0.3V to +6V

ISET, CCV, PWMO, FSET, OSC,

OV to GND................................................-0.3V to V

CC

+ 0.3V

Continuous Power Dissipation (T

A

= +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 _______________________________________________________________________________________

IN Input Voltage Range

IN Quiescent Current

IN Quiescent Current MAX17061 is disabled, V

VCC Output Voltage

VCC Current Limit V

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

OSC High-Level Threshold

OSC Midlevel Threshold 1.5

OSC Low-Level Threshold 0.4 V

Minimum Duty Cycle

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

PARAMETER CONDITIONS MIN TYP MAX UNITS

V

= V

IN

CC

V

= open 5.5 26.0

CC

MAX17061 is enabled at
minimum brightness, no load

M AX 17061 i s enab l ed , 6V < V

MAX17061 is disabled, V

is forced to 4.5V 15 40 70 mA

C C

V

= V

V
V

OSC

OSC

OSC

CC

= open 675 750 825Operating Frequency
= GND 450 500 550

4.5 5.5

VIN = 26V

V

= VCC = 5V

IN

= 12V 10 µA

I N

< 26V , 0 < I

I N

12V 3.90 4.35 4.80

I N =

< 10m A 4.7 5.0 5.3

V C C

1.24 2 mA

0.9 1.0 1.1 MHz

V

-

CC

0.4

V

PWM mode (Note 1) 10
Pulse skipping, no load (Note 1) 0

V

CC

2.0

-

V

V

kHz

V

%

MAX17061

8-String White LED Driver with

SMBus for LCD Panel Applications

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VIN= 12V, C

CCV

= 0.022µF, R

CCV

= 5.1kΩ, V

ISET

= V

OSC

= VDD= VCC, R

FSET

= 464kΩ, V

PWMI

= GND,

T

A

= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

INPUT LEAKAGE

PWMI Leakage Current -0.3 +0.3 µA
ISET, FSET Leakage Current ISET , FSET to V
OV Leakage Current -0.1 +0.1 µA
SDA, SCL Input Bias Current -1 +1 µA
SDA Output Low-Sink Current V
OSC Leakage Current -3 +3 µA

LED CURRENT

Full-Scale FB_ Output Current

ISET High-Level Threshold

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 %

Minimum FB_ Regulation Voltage

Maximum FB_ Ripple I
FB_ On-Resistance V

FB_ Leakage Current

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)

Thermal-Shutdown Threshold (Note 1) 160 °C
Over cur r ent FAU LT S hutd ow n Ti m er I
FB_ Overvoltage Fault Timer Full brightness 1.7 2 2.3 ms

PARAMETER CONDITIONS MIN TYP MAX UNITS

= 0.4V 4 mA

SDA

ISET = V
R
R
R

I
I
I
I

V
V

CC

133kΩ 28.8 30.0 31.2

ISET =

= 200kΩ 19.3 20.0 20.7

ISET

266kΩ 14.4 15.0 15.6

ISET =

= 25mA 475 625 910

FB_

= 30mA 575 750 1100

FB_

= 20mA 380 500 740

FB_

= 15mA 285 375 560

FB_

= 20mA (C

FB_

= 50mV (includes 10Ω sense resistor) 17.5 28.4 Ω

FB_

= 26V, TA = +25°C 1

FB_

= 45V, TA = +25°C 2.5 4

FB_

CC

OUT

= 1µF, V

+1 µA

24.5 25.0 25.5

V

-

CC

0.4

= VCC) (Note1) 120 200 mV

OSC

V

48 84 120 mV

> 3.3A at duty = 0% 88 128 168 µs

PEAK

mA

mV

P/P

µA

MAX17061

8-String White LED Driver with
SMBus for LCD Panel Applications

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VIN= 12V, C

CCV

= 0.022µF, R

CCV

= 5.1kΩ, V

ISET

= V

OSC

= VDD= VCC, R

FSET

= 464kΩ, V

PWMI

= GND,

T

A

= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VIN= 12V, C

CCV

= 0.022µF, R

CCV

= 5.1kΩ, V

ISET

= V

OSC

= VDD= VCC, R

FSET

= 464kΩ, V

PWMI

= GND,

T

A

= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 2)

PARAMETER CONDITIONS MIN TYP MAX UNITS

PWM FILTER

PWM Output Impedance 20 40 60 kΩ

DPWM Oscillator Frequency

PWMI Input-Frequency Range 5 10 100 kHz
PWMI Full-Range Accuracy 5 LSB

PWMI Brightness Setting

SMBus TIMING SPECIFICATION

SMBus Frequency FSMB 10 100 kHz
Bus Free Time TBUF 4.7 µs

START Condition Hold
Time from SCL

START Condition Setup
Time from SCL

STOP Condition Setup
Time from SCL

SDA Hold Time from SCL THD:DAT 300 ns
SDA Setup Time from SCL TSU:DAT 250 ns

SCL Low Period T

SCL High Period T

R

FSET

R

FSET

R

FSET

R

FSET

= 464kΩ 197 200 203
= 113kΩ 750 785 820
= 65kΩ 1.270 1.335 1.400
= 42kΩ 2

PWMI duty cycle = 100% 98 100
PWMI duty cycle = 50% 48 50 52
PWMI duty cycle = 0% 2.6 2.7 2.8

THD:STA 4

TSU:STA 4.7

TSU:STO 4

LOW

HIGH

4.7 µs
4 µs

µs

µs

µs

Hz

kHz

%

IN Input Voltage Range

IN Quiescent Current

VCC Output Voltage

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

PARAMETER CONDITIONS MIN TYP MAX UNITS

V

= V

IN

CC

4.5 5.5

VCC = open 5.5 26.0

MAX17061 is enabled at
minimum brightness, no load

MAX17061 is disabled, V

MAX17061 is enabled, 6V < VIN < 26V, 0 < I

MAX17061 is disabled, V

VIN = 26V 2

V

= VCC = 5V 2

IN

= 12V 10 µA

IN

< 10mA 4.7 5.3

VCC

= 12V 3.9 4.8

IN

V

mA

V

MAX17061

8-String White LED Driver with

SMBus for LCD Panel Applications

_______________________________________________________________________________________ 5

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VIN= 12V, C

CCV

= 0.022µF, R

CCV

= 5.1kΩ, V

ISET

= V

OSC

= VDD= VCC, R

FSET

= 464kΩ, V

PWMI

= GND,

T

A

= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 2)

BOOST CONVERTER

LX On-Resistance 20mA from LX_ to PGND 0.3 Ω
LX Leakage Current 45V on LX_ 1 µA

OSC High-Level Threshold

OSC Midlevel Threshold 1.5

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 V
OV Leakage Current -0.1 +0.1 µA
SDA, SCL Input Bias Current -1 +1 µA
SDA Output-Low Sink Current V
OSC Leakage Current -3 +3 µA

LED CURRENT

Full-Scale FB_ Output Current

ISET High-Level Threshold

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 %

Minimum FB_ Regulation Voltage

Maximum FB_ Ripple I
FB_ On-Resistance V

PARAMETER CONDITIONS MIN TYP MAX UNITS

V

= V

OSC

V

OSC

V

OSC

SDA

ISET = V
R

ISET =

R

ISET

R

ISET =

I

FB_

I

FB_

I

FB_

I

FB_

FB_

FB_

CC

= open 675 825 kHzOperating Frequency
= GND 450 560 kHz

= 0.4V 4 mA

CC

133kΩ 28.6 31.4

= 200kΩ 19.0 21.0

266kΩ 14.3 15.7

= 25mA 425 910
= 30mA 575 1100
= 20mA 380 740
= 15mA 285 560

= 20mA (C

= 50mV (includes 10Ω sense resistor) 28.4 Ω

CC

OUT

= 1µF, V

0.89 1.10 MHz

V

-

CC

0.4

V

+1 µA

24.5 25.5

V

-

CC

0.4

= VCC) 200 mV

OSC

V

V

CC

2.0

-

V

mA

mV

P/P

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, C

CCV

= 0.022µF, R

CCV

= 5.1kΩ, V

ISET

= V

OSC

= VDD= VCC, R

FSET

= 464kΩ, V

PWMI

= GND,

T

A

= -40°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.) (Note 2)

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)

Over cur r ent FAU LT S hutd ow n Ti m er I
FB_ Overvoltage Fault Timer 1.6 2.4 ms

PARAMETER CONDITIONS MIN TYP MAX UNITS

PWM FILTER

PWM Output Impedance 20 60 kΩ

PWMI Input Frequency Range 5 100 kHz
PWMI Full-Range Accuracy 5 LSB

PWMI Brightness Setting

SMBus TIMING SPECIFICATION

SMBus Frequency FSMB 10 100 kHz
Bus Free Time TBUF 4.7 µs

START Condition Hold
Time from SCL

START Condition Setup
Time from SCL

STOP Condition Setup
Time from SCL

SDA Hold Time from SCL THD:DAT 300 ns
SDA Setup Time from SCL TSU:DAT 250 ns

SCL Low Period T

SCL High Period T

48 120 mV

> 3.3A at duty = 0% 88 168 µs

PEAK

R

= 464kΩ 197 203 kHz

FSET

R

= 113kΩ 750 820 HzDPWM Oscillator Frequency

FSET

R

= 65kΩ 1.27 1.40 kHz

FSET

PWMI duty cycle = 100% 98
PWMI duty cycle = 50% 48 52
PWMI duty cycle = 0% 2.6 2.8

THD:STA 4

TSU:STA 4.7

TSU:STO 4

LOW

HIGH

4.7 µs
4 µs

µs

µs

µs

%

MAX17061

8-String White LED Driver with

SMBus for LCD Panel Applications

_______________________________________________________________________________________

7

Typical Operating Characteristics

(Circuit of Figure 1, VIN= 12V, C

CCV

= 0.022µF, R

CCV

= 5.1kΩ, V

ISET

= V

OSC

= VDD= VCC, R

FSET

= 464kΩ, V

PWMI

= GND, LEDs =

10 series x 4 parallel strings, T

A

= +25°C, unless otherwise noted.)

BOOST CONVERTER EFFICIENCY

vs. INPUT VOLTAGE (BRIGHTNESS = 100%)

90

89

88

87

86

BOOST CONVERTER EFFICIENCY (%)

85

7

INPUT VOLTAGE (V)

LED CURRENT vs. AMBIENT TEMPERATURE

26.0

25.8

25.6

25.4

25.2

25.0

24.8

LED CURRENT (mA)

24.6

24.4

24.2

24.0

0

vs. SMBus BRIGHTNESS SETTING

30

25

MAX17061 toc01

20

15

LED CURRENT (mA)

10

5

19161310

0

SMBus BRIGHTNESS SETTING

(BRIGHTNESS = 100%)

MAX17061 toc04

60 804020

AMBIENT TEMPERATURE (°C)

LED CURRENT

200 250150100500

30

25

20

15

LED CURRENT (mA)

10

5

0

5

30

25

MAX17061 toc02

20

15

LED CURRENT (mA)

10

5

0

0

LED CURRENT

vs. INPUT VOLTAGE

SMBus = 0xFF

INPUT VOLTAGE (V)

vs. PWMI DUTY CYCLE

PWMI DUTY CYCLE (%)

SMBus = 0x1F

LED CURRENT

SMBus = 255

MAX17061 toc05

17 2014118

MAX17061 toc03

SMBus = 128

80 100604020

5

4

SMBus = 255

3

2

SUPPLY CURRENT (mA)

1

0

5

SUPPLY CURRENT

vs. INPUT VOLTAGE

SMBus = 0

INPUT VOLTAGE (V)

10

MAX17061 toc06

17 2014118

8

6

4

SHUTDOWN CURRENT (μA)

2

0

SHUTDOWN CURRENT

vs. INPUT VOLTAGE

5

MAX17061 toc07

17 2014118

INPUT VOLTAGE (V)

MAX17061

8-String White LED Driver with
SMBus for LCD Panel Applications

8 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN= 12V, C

CCV

= 0.022µF, R

CCV

= 5.1kΩ, V

ISET

= V

OSC

= VDD= VCC, R

FSET

= 464kΩ, V

PWMI

= GND, LEDs =

10 series x 4 parallel strings, T

A

= +25°C, unless otherwise noted.)

SWITCHING WAVEFORMS

(V

IN

= 7V, BRIGHTNESS = 100%)

MAX17061 toc08

1μs/div

V

LX

20V/div

I

L

200mA/div

0V

0mA

SWITCHING WAVEFORMS

(V

IN

= 20V, BRIGHTNESS = 100%)

MAX17061 toc09

1μs/div

V

LX

20V/div

I

L

200mA/div

0V

0mA

STARTUP WAVEFORMS

(BRIGHTNESS = 100%)

MAX17061 toc10

400μs/div

V

LX

20V/div

I

L

1A/div

V

OUT

20V/div

V

CCV

2V/div

0V

0V

0V

0A

STARTUP WAVEFORMS

(SMBus = 0x04)

MAX17061 toc11

400μs/div

V

LX

20V/div

I

L

1A/div

V

OUT

20V/div

V

CCV

2V/div

0V

0V

0V

0A

LED CURRENT WAVEFORMS

(SMBus = 0x80)

MAX17061 toc12

2ms/div

V

FB1

10V/div

I

L

500mA/div

I

LED

20mA/div

V

OUT

20V/div

0V

0mA

0mA

0V

LED CURRENT WAVEFORMS

(SMBus = 0x04)

MAX17061 toc13

2ms/div

V

FB1

10V/div

I

L

500mA/div

I

LED

20mA/div

V

OUT

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, C

CCV

= 0.022µF, R

CCV

= 5.1kΩ, V

ISET

= V

OSC

= VDD= VCC, R

FSET

= 464kΩ, V

PWMI

= GND, LEDs =

10 series x 4 parallel strings, T

A

= +25°C, unless otherwise noted.)

LED-OPEN FAULT PROTECTION

(BRIGHTNESS = 100%, LED OPEN ON FB1)

MAX17061 toc14

400μs/div

V

FB1

1V/div

I

FB2

20mA/div

I

FB2

10V/div

V

OUT

20V/div

0V

0V

0V

0mA

LED-SHORT FAULT PROTECTION

(BRT = 100%, 2 LEDs SHORT ON FB1)

MAX17061 toc15

1ms/div

V

FB1

5V/div

V

FB2

10V/div

I

FB2

20mA/div

I

FB1

20mA/div

0V

0V

0mA

0mA

LINE TRANSIENT RESPONSE

(V

IN

= 12V→19V, BRIGHTNESS = 100%)

MAX17061 toc16

100μs/div

V

OUT

20V/div

I

L

1A/div

I

FB1

20mA/div

V

IN

10V/div

0V

0V

0A

0mA

LINE TRANSIENT RESPONSE

(V

IN

= 19V→12V, BRIGHTNESS = 100%)

MAX17061 toc17

100μs/div

V

OUT

20V/div

I

L

1A/div

I

FB1

20mA/div

V

IN

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

2 FB4

3 GND Analog Ground

4, 6, 18 N.C. No Connection

5 FB5

7 FB6

8 FB7

9 FB8

10 OSC

11 PWMI

12 PWMO

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 V

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 V

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 V

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 V

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 V

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 V

O sci l l ator Fr eq uency- S el ecti on P i n. C onnect OS C to V
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.

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.

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.

to set the step - up conver ter ’ s osci l l ator fr eq uency to

C C

.

CC

.

CC

.

CC

.

CC

.

CC

.

CC

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:

9

f

13 FSET

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

17 LX1

19 PGND2 Boost Regulator Power Ground

20 PGND1 Boost Regulator Power Ground

21 IN

Boost Regulator Internal MOSFET Drain. Connect the inductor and the Schottky diode to LX2 node. LX2
should always be shorted to LX1 externally.

Boost Regulator Internal MOSFET Drain. Connect the inductor and the Schottky diode to LX1 node. LX1
should always be shorted to LX2 externally.

Supply Input, 4.5V to 26V. V
GND directly at the pin with a 0.1µF or greater ceramic capacitor.

biases the internal 5V linear regulator that powers the device. Bypass IN to

IN

DPWM

10

=

R

×+

αγ[]Ω

MAX17061

8-String White LED Driver with

SMBus for LCD Panel Applications

______________________________________________________________________________________ 11

Pin Description (continued)

Detailed Description

The MAX17061 is a high-efficiency driver for arrays of
white LEDs. It contains a fixed-frequency current­mode PWM step-up controller, a 5V linear regulator,
dimming control circuit, SMBus interface, internal
power MOSFET, and eight regulated current sources
(see Figure 2). When enabled, the step-up controller
boosts the output voltage to provide sufficient head­room for the current sources to regulate their respec­tive string currents. The MAX17061 features selectable
switching frequency (500kHz, 750kHz, or 1MHz), which
allows trade-offs between external component size and
operating efficiency. The control architecture automati­cally skips pulses at light loads to improve efficiency
and prevents overcharging the output capacitor.

WLED brightness is controlled by turning the WLEDs
on and off with a DPWM signal. The DPWM frequency
can be accurately adjusted with a resistor. The bright­ness of the LEDs is proportional to the duty cycle of the
DPWM signal, which is controlled externally through
either a PWM or 2-wire SMBus-compatible interface, or

both. When both interfaces are used at the same time,
the product of the PWM duty cycle and SMBus com­mand value is used for the dimming control. This
DPWM control scheme provides a full dimming range
with 8-bit resolution.

The MAX17061 has multiple features to protect the con­troller 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 V

CC

, short fault is detected
and the respective current source is disabled. In either
LED open or short conditions, the fault strings are dis­abled while other strings can still operate normally. The
controller features cycle-by-cycle current limit to provide
stable operation and soft-start protection. In a current­limit condition, the controller shuts down after a 128µs
overcurrent fault timer expires. A thermal-shutdown cir­cuit provides another level of protection.

PIN NAME FUNCTION

22 V

23 V

24 CCV

25 OV

26 ISET

27 FB1

28 FB2

—EP

Boost Reg ul ator M OS FE T G ate D r i ve S up p l y. Byp ass V

DD

5V Linear Regulator Output. VCC provides power to the MAX17061. Bypass VCC to GND with a ceramic
capacitor of 1µF or greater. If V

CC

external 5V supply to V

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.

Overvoltage Sense. Connect OV to the center tap of a resistive voltage-divider from V
detection threshold for voltage limiting at OV is 1.236V (typ).

Full-Scale LED Current Adjustment Pin. The resistance from ISET to GND controls the full-scale current in
each LED string:

The acceptable resistance range is 133kΩ < R
30mA > I

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 V

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 V

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.

LEDMAX

CC

> 15mA. Connect ISET to VCC for a default full-scale LED current of 25mA.

is less than or equal to 5.5V, tie V

IN

.

I

= 20mA x 200kΩ/R

LEDMAX

ISET

to G N D w i th a cer am i c cap aci tor of 1µF or g r eater .

D D

< 266kΩ, which corresponds to full-scale LED current of

to IN to disable internal LDO and use

CC

to ground. The

OUT

ISET

.

CC

.

CC

MAX17061

The MAX17061 includes a 5V linear regulator that pro­vides the internal bias and gate drive for the step-up
controller. When an external 5V is available, the internal
LDO can be overdriven to decrease power dissipation.
Otherwise, connect the IN pin to an input greater than 5.5V.

Fixed-Frequency Step-Up Controller

The MAX17061’s fixed-frequency, current-mode, step­up controller automatically chooses the lowest active
FB_ voltage to regulate the output voltage. Specifically,
the 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 peak­inductor current. The slope-compensation signal is
added to the current-sense signal to improve stability at
high duty cycles.

When the input voltage is close to the output voltage, the
MAX17061 automatically skips pulses to prevent over­charging the output capacitor. In SKIP mode, the induc­tor current ramps up for a minimum on-time of
approximately 90ns, and then discharges the stored
energy to the output. The switch remains off until another
pulse is needed to boost the output voltage.

Internal 5V Linear Regulator

V

CC

and UVLO

The MAX17061 includes an internal low-dropout linear
regulator (VCC). When VINis higher than 5.5V, this lin­ear regulator generates a 5V supply to power internal
PWM controller, control logic, and MOSFET driver. The
VCCvoltage drops to 4.35V in shutdown. If VINis less
than or equal to 5.5V, VCCand IN can be tied together
and powered from an external 5V supply. There is an
internal diode from VCCto IN, so VINmust be greater
than VCC(see Figure 3).

8-String White LED Driver with
SMBus for LCD Panel Applications

12 ______________________________________________________________________________________

Figure 1. Typical Operating Circuit

V

IN

7V TO 21V

4.7μF

0.1μF

V

DD

V

CC

OSC
ISET

FSET

CCV

MAX17061

464kΩ

1μF

5.1kΩ

220pF

0.022μF

L1

10μH

IN

LX1
LX2

PGND1

PGND2

OV

D1

2μF

C

OUT

2.21MΩ

R2

61.9kΩ

R1

V

OUT

UP TO 45V

PWMIPWM
PWMO

1μF

SCLCLK

SDADATA

GND

EP

FB1
FB2
FB3
FB4
FB5
FB6

FB7

FB8

V

CC

MAX17061

8-String White LED Driver with

SMBus for LCD Panel Applications

______________________________________________________________________________________ 13

Figure 2. Control Circuit Block Diagram

V

OSC

CCV

ISET

OUTPUT OVERVOLTAGE

MAX17061

V

VSAT

ERROR

COMPARATOR

+ 0.6V

CC

IN

CC

5V LINEAR

REGULATOR

V

CC

OSCILLATOR

3-LEVEL

COMPARATOR

REF ADJ

CLOCK

SLOPE

COMPENSATION

FB OVERVOLTAGE

COMPARATOR

OV FAULT

ERROR

AMPLIFIER

gm

REF

8-BIT D/A

COMPARATOR

CONTROL AND
DRIVER LOGIC

CURRENT SENSE

HVC

LVC

EN

FB8

FB7

FB6

FB5

FB4

FB3

FB2

1.236V

OV

V

DD

LX1, 2

PGND1, 2

FB1

FSET

PWMO

PWMI

DIMMING

BLOCK DIAGRAM

SDA

SCL

A

D

"< = 1"

"1"

PWM_MD

0x03

0x02 0x01 0x00

INTERFACE

DPWM SIGNAL GENERATOR

DPWM

SETTING

MUX

PWM_SEL

SMBus

MUX

WLED
ON/OFF

CURRENT SOURCE

CURRENT SOURCE

CURRENT SOURCE

CURRENT SOURCE

CURRENT SOURCE

CURRENT SOURCE

CURRENT SOURCE

CURRENT SOURCE

10Ω

GND

FB2

FB3

FB4

FB5

FB6

FB7

FB8

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 VCCrises above 2.8V (typ).
The controller is disabled until VCCexceeds the UVLO
threshold of 4.25V (typ). Hysteresis on UVLO is approx­imately 85mV.

The VCCand VDDpins should be bypassed to GND
with a minimum 1µF ceramic capacitor.

Startup

At startup, the MAX17061 checks the OV pin to see if
the Schottky diode is open. If the OV voltage is lower
than 84mV (typ), the boost converter does not start.
After the OV test is done, the MAX17061 performs a
diagnostic test of the LED array. The test is divided to
two phases; each phase takes approximately 1.024ms.
In the first test phase, all FB_ inputs are quickly dis­charged down to 5.6V (typ) and then continuously dis­charged by 800µA (typ) current sources. If a given FB_
voltage remains higher than 5.6V (typ), the string is
considered to be shorted. Otherwise, if a given FB_

voltage is higher than 3V (typ), the string is considered
to be unused. Unused strings should be tied to VCC. In
the second phase, each FB_ is precharged by an inter­nal 400µA (typ) current source. If a given FB_ voltage
remains lower than 1V (typ), the FB_ is considered to
be a short to GND and the device is 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 clear­ing bit 0 of the device control register (0x01). When a
critical failure is detected, the IC also enters shutdown
mode. In shutdown mode, all functions of the IC are
turned off including the 5V linear regulator. Only a
crude linear 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 shut­down. When bit 0 of the device control register (0x01)
is set to 1, the MAX17061 exits shutdown mode and
starts. The fault/status register is reset at startup.

8-String White LED Driver with
SMBus for LCD Panel Applications

14 ______________________________________________________________________________________

Figure 3. Low-Input-Voltage Application Circuit

V

IN

2.8V TO 5.5V

4.7μF

0.1μF

L1

2.2μH

D1

2μF

V

OUT

UP TO 45V

464kΩ

EXTERNAL

5V SUPPLY

1μF

1μF

5.1kΩ

0.022μF

220pF

V

DD

V

CC

OSC
ISET

FSET

CCV

PWMIPWM
PWMO

SCLCLK

SDADATA

GND

IN

MAX17061

EP

LX1
LX2

PGND1

PGND2

FB1
FB2
FB3
FB4
FB5
FB6

FB7

FB8

R1

OV

2.21MΩ

R2

61.9kΩ

V

CC

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 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, V

OV

, exceeds

1.236V, a comparator turns off the internal power MOS­FET. This step-up converter switch is reenabled after
the VOVdrops 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
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 fre­quencies of up to 2kHz. All LED full-scale currents are
identical and are set through the ISET pin (15mA < I

LED

< 30mA). When ISET is connected to VCC, the LED full­scale current is set at the 25mA default value.

The minimum voltage drop across each current source
is approximately 625mV when the LED current is 25mA.
The low-voltage drop helps reduce dissipation while
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 VCCat 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 V

CC

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 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 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 unaf­fected LED strings to operate normally. The LED short­protection 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 R

FSET

= 464kΩ. The
duty cycle of this DPWM signal can be controlled exter­nally through two interfaces: PWM and SMBus. The
ISET pin sets the amplitude of the current sources for
each LED string (Figure 4). The internal DPWM signal
directly 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.

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

V

CC

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 < R

ISET

<
266kΩ, which corresponds to full-scale LED current of
30mA > I

LEDMAX

> 15mA. Connect ISET to VCCfor 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, R

FSET

, is
from 42kΩ to 464kΩ, corresponding to the DPWM fre­quency of 200Hz to 2kHz.

Dimming Control Interfaces

The MAX17061’s dimming control circuit consists of
two interfaces: PWM and SMBus. The block diagram of
these two input interfaces is shown in Figure 5. The
dimming can be performed in three modes: PWM,
SMBus, or DPST. In PWM mode, the brightness is
adjusted by the PWM signal applied to the PWMI pin. In
SMBus mode, the brightness is adjusted by an I2C
command from uplink processor through the 2-wire
SMBus. In DPST mode, the brightness is adjusted by
the product of the PWM duty cycle and SMBus com­mand value. This DPWM control provides a dimming
range with 8-bit resolution down to 2.7% and supports
Intel DPST to maximize battery life.

f

R

DPWM

=

×+

10

9

αγ[]Ω

I

mA k

R

LEDMAX

ISET

=

×20 200 Ω

8-String White LED Driver with
SMBus for LCD Panel Applications

16 ______________________________________________________________________________________

Figure 5. MAX17061 PWM and SMBus Interface Circuit

D = 30%

D = 12.5%

D = 6.25%

DPWM

0A

I

LEDMAX

I

LED

D = 50%

D =

t

ON

t

ON

t

DPWM

t

DPWM

DPWM DIMMING MODE

Figure 4. LED Current Control by DPWM Signal in Dimming

PWMO

PWMI

SDA
SCL

BUFFER

A

D

SMBus AND PWM INPUT BLOCK

IDENTIFICATION

REGISTER

0x03

FAULT/STATUS

REGISTER

0x02 0x01 0x00

< = 1

PWM_MD

1

SMBus

INTERFACE

MUX

CONTROL
REGISTER

DIGITAL

MULTIPLIER

DEVICE

PWM_SEL

DPWM

SETTING

MUX

BACKLIGHT

ON/OFF

BRIGHTNESS

CONTROL
REGISTER

Overvoltage Protection

The SMBus interface can be used to adjust the dim­ming, 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 VCCpin 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 oper­ating 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 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.

MAX17061

8-String White LED Driver with

SMBus for LCD Panel Applications

______________________________________________________________________________________ 17

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.

Bit field definitions:

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:

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 FIELD DEFINITION DESCRIPTION

Bit [7..0] BRT [7..0] 8-bit brightness setting, adjusting brightness levels in 256 steps, default value is 0xFF.

REGISTER 0x01 DEVICE CONTROL REGISTER DEFAULT VALUE 0x00

RESERVED RESERVED RESERVED RESERVED RESERVED PWM_MD PWM_SEL BL_CTL

Bit 7 Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 (R/W) Bit 1 (R/W) Bit 0 (R/W)

BIT 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

Bit 0

MAX17061

8-String White LED Driver with
SMBus for LCD Panel Applications

18 ______________________________________________________________________________________

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:

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

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

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)

THRM_SHD

Thermal shutdown (1 = thermal fault, 0 = thermal OK)

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

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 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

At light loads, the MAX17061 automatically skips pulses
to improve efficiency and prevent overcharging the output
capacitor. The output current for the converter SKIP oper­ation can be calculated by the following equation:

where I

O(SKIP)

is the output current in SKIP mode, V

IN

is the input voltage, T

ON(MIN)

is the minimum on-time,

and V

DIODE

is the forward voltage of rectifier diode D.

I

VT 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

Table 4. Component List

Table 5. Component Suppliers

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

SWITCHING

FREQUENCY

White LED

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

Input Capacitors

Nichia NSSW008C

3.2V (typ), 3.5V (max) at 20mA

10µH, 1.2A power inductor
TDK VLP6810T-100M1R2; Sumida CR6D09HPNP-100MC

4.7µF ±10%, 25V X5R ceramic capacitor (1206)
Murata GRM319R61E475KA12D

1MHz 1MHz

Nichia NSSW008C

3.2V (typ), 3.5V (max) at 20mA

10µH, 2.5A power inductor
TDK SLF10145T-100M2R5-PF

10µF ±10%, 25V X5R ceramic capacitor (1206)
Murata GRM31CR61E106KA

Output Capacitor
C

OUT

Diode Rectifier

0.33µF ±10%, 50V X7R ceramic capacitor (1206) (6x)
Murata GRM319R71H334K
TDK C3216JB1H334K

0.7A, 60V Schottky diode (US-flat)
Toshiba CUS04

1µF ±10%, 50V X7R ceramic capacitor (1206) (4x)
Murata GRM31MR71H105KA
TDK C3216X7R1H105K

3A, 60V Schottky diode
Nihon EC31QS06

SUPPLIER PHONE WEBSITE

Murata 770-436-1300 www.murata.com

Nichia 248-352-6575 www.nichia.com

Sumida 847-545-6700 www.sumida.com

Toshiba 949-455-2000 www.toshiba.com/taec

Vishay 203-268-6261 www.vishay.com

MAX17061

To ensure the stable operation, the MAX17061 includes
slope compensation, which sets the minimum inductor
value. In continuous-conduction mode (CCM), the mini­mum inductor value is calculated with the following
equation:

where 24.7mV is a scale factor from the slope compen­sation, the L

CCM(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:

where the L

DCM(MAX)

is the maximum inductor value

for DCM, η is the nominal regulator efficiency (85%),
and I

OUT(MAX)

is the maximum output current.

The output current capability of the step-up converter is
a function of current limit, input voltage, operating fre­quency, and inductor value. Because the slope com­pensation is used to stabilize the feedback loop, the
inductor current limit depends on the duty cycle, and is
determined with the following equation:

where 24.7mV is the scale factor from the slope com­pensation, 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:

where I

LIM

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:

where V

DIODE

is the forward voltage of the rectifier

diode and R

ON

is the internal MOSFET’s on-resistance

(0.15Ω typ).

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, tran­sient response time, output voltage ripple, and cost.

The maximum output current, input voltage, output volt­age, and switching frequency determine the inductor
value. Very high inductance minimizes the current rip­ple, and therefore reduces the peak current, which
decreases core losses in the inductor and I2R losses in
the entire power path. However, large inductor values
also require more energy storage and more turns of
wire, which 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, inde­pendent of the internal slope compensation mode, but
there is a maximum inductor value requirement to
ensure the DCM operating mode.

I

LI f

VV V

OUT DCM MAX

LIM OSC

OUT DIODE IN

_()

=

×××

×+ −

()

2

2

η

D

VVV

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

2

η

L

VVVR

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 cur­rent. The controller operates in DCM mode when LIR is
higher than 2.0, and it works in CCM mode when LIR is
lower than 2.0. The best trade-off between inductor size
and converter efficiency for step-up regulators generally
has an LIR between 0.3 and 0.5. However, depending
on the AC characteristics of the inductor core material
and ratio of inductor resistance to other power-path
resistances, the best LIR can shift up or down. If the
inductor resistance is relatively high, more ripples can
be accepted to reduce the number of required turns and
increase the wire diameter. If the inductor resistance is
relatively low, increasing inductance to lower the peak
current can reduce losses throughout the power path. If
extremely thin high-resistance inductors are used, as is
common for LCD panel applications, LIR higher than 2.0
can be chosen for DCM operating mode.

Once a physical inductor is chosen, higher and lower val­ues of the inductor should be evaluated for efficiency
improvements in typical operating regions. The 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 (I

OUT(MAX)

), the expected efficiency (

η

TYP

)

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 compensa­tion, and the RSis the equivalent current-sensing scale
factor (12mΩ typ):

1) Choose an available inductor value from an appropri­ate inductor family. Calculate the maximum DC input
current at the minimum input voltage V

IN(MIN),

using
conservation of energy and the expected efficiency
at that operating point (

η

MIN

) 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 fol­lowing equation:

The inductor’s saturation current rating should exceed
I

PEAK

and the inductor’s DC current rating should

exceed I

IN(DC,MAX)

. For good efficiency, choose an

inductor with less than 0.1Ω series resistance.

Inductor Selection Design

Examples:

Considering the

Typical Operating Circuit

with four
10-LED strings and 25mA LED full-scale current, the
maximum load current (I

OUT(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 L

CCM(MIN):

A10µH inductor is chosen, which is higher than the
minimum L that guarantees stability in CCM.

L

VV Vm

mV MHz

H

CCM MIN()

..

..

.=

+−×

()

×

××

=

35 9 0 4 2 7 12

2247 09

60Ωμ

L

V

V

VV

mA MHz

H=

⎛
⎝

⎜

⎞
⎠

⎟

−

×

⎛
⎝

⎜

⎞
⎠

⎟

⎛
⎝

⎜

⎞
⎠

⎟

=

7

35 9

35 9 7

100 1

085

1

944

2

.

..

. μ

II

I

PEAK IN DC MAX

RIPPLE

=+

(, )

2

L

V

VV

V

fVI

DCM MAX

IN MIN

OUT MAX DIODE

IN MIN

OSC MAX OUT MAX OUT MAX

()

()

()

()

() () ()

=−

+

⎛

⎝

⎜

⎞

⎠

⎟

×

×

×× ×

1

2

2

η

I

VV V

LV f

RIPPLE

IN MIN OUT MAX IN MIN

OUT MAX OSC

=

×−

()

××

() ( ) ()

()

I

IV

V

IN DCMAX

OUT MAX OUT

IN MIN MIN

(, )

()

()

=

×

×η

L

VVVR

mV f

CCM MIN

OUT MAX DIODE IN MIN S

OSC MIN

()

() ()

()

.

=

+−×

()

×

××

2

2247

L

V

V

VV

I f LIR

IN MIN

OUT

OUT IN MIN

OUT MAX OSC

TYP

=

⎛
⎝

⎜

⎞
⎠

⎟

−
×

⎛

⎝

⎜

⎞

⎠

⎟

⎛
⎝

⎜

⎞
⎠

⎟

__

()

2

η

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 I

PEAK

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 200mV

P-P

. For ceramic capacitors, the out-

put voltage ripple is typically dominated by V

RIPPLE(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 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 I

PEAK

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 out­put 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 V

OV_TH

, typically 1.23V, OV protection is acti­vated. 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 injec­tion into the IC. A 10µF ceramic capacitor is used in the

Typical Operating Circuit

(Figure 1) because of the
high source impedance seen in typical lab setups.
Actual 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, CINcan be reduced below the val­ues used in the

Typical Operating Circuit

(Figure 1).
Ensure a low-noise supply at IN by using adequate CIN.
Alternatively, greater voltage variation can be tolerated
on CINif IN is decoupled from CINusing an RC low­pass filter.

VV

M

k

V

OUT OVP()

.(

.

.

)=×+ ≈1 236 1

221

61 9

45

Ω

Ω

VV

R

R

OUT OVP OV TH() _

=×+

⎛
⎝

⎜

⎞
⎠

⎟

1

1
2

VIR

RIPPLE ESR PEAK ESR COUT() ( )

≈

V

I

C

VV

Vf

RIPPLE C

OUT MAX

OUT

OUT MAX IN MIN

OUT MAX OSC

()

() () ()

()

≈

−

⎛

⎝

⎜

⎞

⎠

⎟

VV V

RIPPLE RIPPLE C RIPPLE ESR

=+

() ( )

I

mA 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

...

.. . ..

.

L

V

VV

V

MHz V mA

H

DCM MAX()

..

() .

..

.

=−

+

⎛
⎝

⎜

⎞
⎠

⎟

×

×

×××

=

1

7

35 9 0 4

7085

2 0 825 35 9 100

56

2

μ

I

mA 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 regula­tor performance. LED characteristics vary significantly
from manufacturer to manufacturer. Consult the respec­tive LED data sheets to determine the range of output
voltages for a given brightness and LED current. In gen­eral, brightness increases as a function of bias current.
This suggests that the number of LEDs could be
decreased if higher bias current is chosen; however,
high current increases LED temperature and reduces
operating life. Improvements in LED technology are
resulting in devices with lower forward voltage 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 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 V

FB_

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 short­protection circuit disables the high FB string.

FB Pin Maximum Voltage

The current through each FB_ pin is controlled only
during the step-up converter’s on-time. During the con­verter’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 capac­itor to avoid excessive switching noise.

2) Connect high-current input and output components

with short and wide connections. The high-current
input loop goes from the positive terminal of the input
capacitor to the inductor, to the internal MOSFET,
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, 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 ter­minal 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 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 cen­ter trace should be kept short. Placing the resistors
far away causes the sensing trace to become
antennas that can pick up switching noise. Avoid
running the sensing traces near LX.

5) Place IN pin bypass capacitor as close as possible
to the device. The ground connection of the IN
bypass capacitor should be connected directly to
GND pins with a wide trace.

6) Minimize the size of the LX node while keeping it
wide and short. Keep the LX node away from the
feedback node and ground. If possible, avoid run­ning the LX node from one side of the PCB to the
other. Use DC traces as shield if necessary.

Refer to the MAX17061 evaluation kit for an example of
proper board layout.

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.

LX1INLX2

SCL

12OV4567

2021 19 17 16 15

ISET

FB1

PWMO

PWMI

OSC

FB8

MAX17061ETI+

GND

PGND2

3

18

28

8

FB2

FB7

CCV

23

13

FSET

V

CC

22

14

SDA

V

DD

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

.)