MAX17061AETI+T - Maxim Integrated

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

VIN

LX1, 2

FB2

FB3

FB4

FB5

FB6

FB7

FB8

L1 D1

VDD

ISET

FSET

VCC

PWMIPWM

MAX17061A

VOUT

SCLCLK

SDADATA

OSCN.C.

GND

PWMO

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

Simplied 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

www.maximintegrated.com Maxim Integrated

│

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

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

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

www.maximintegrated.com Maxim Integrated

│

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

www.maximintegrated.com Maxim Integrated

│

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

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

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

www.maximintegrated.com Maxim Integrated

│

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

www.maximintegrated.com Maxim Integrated

│

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

LED CURRENT

vs. PWMI DUTY CYCLE

MAX17061A toc03

PWMI DUTY CYCLE (%)

LED CURRENT (mA)

80 100604020

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

LED CURRENT

vs. INPUT VOLTAGE

MAX17061A toc05

LED CURRENT (mA)

17 2014118

SMBus = 0xFF

SMBus = 0x1F

INPUT VOLTAGE (V)

VCC SUPPLY CURRENT

vs. INPUT VOLTAGE

MAX17061A toc06

SUPPLY CURRENT (mA)

25201510

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

INPUT VOLTAGE (V)

BOOST CONVERTER EFFICIENCY vs.

INPUT VOLTAGE (BRIGHTNESS = 100%)

MAX17061A toc01

INPUT VOLTAGE (V)

BOOST CONVERTER EFFICIENCY (%)

25201510

MAX17061A 8-String White LED Driver with

SMBus for LCD Panel Applications

Maxim Integrated

│

www.maximintegrated.com

Typical Operating Characteristics

(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,

LEDs = 10 series x 4 parallel strings, TA = +25°C, unless otherwise noted.)

STARTUP WAVEFORMS

(BRIGHTNESS = 100%)

MAX17061A toc10

400s/div

VLX

20V/div

1A/div

VOUT

20V/div

VCCV

2V/div

SWITCHING WAVEFORMS

(VIN = 7V, BRIGHTNESS = 100%)

MAX17061A toc08

1s/div

VLX

20V/div

200mA/div

0mA

STARTUP WAVEFORMS

(SMBus = 0x04)

MAX17061A toc11

400s/div

VLX

20V/div

1A/div

VOUT

20V/div

VCCV

2V/div

SWITCHING WAVEFORMS

(VIN = 20V, BRIGHTNESS = 100%)

MAX17061A toc09

1s/div

VLX

20V/div

200mA/div

0mA

LED CURRENT WAVEFORMS

(SMBus = 0x80)

MAX17061A toc12

2ms/div

VFB1

10V/div

500mA/div

ILED

20mA/div

VOUT

20V/div

0mA

LED CURRENT WAVEFORMS

(SMBus = 0x04)

MAX17061A toc13

2ms/div

VFB1

10V/div

500mA/div

ILED

20mA/div

VOUT

20V/div

0mA

MAX17061A 8-String White LED Driver with

SMBus for LCD Panel Applications

Maxim Integrated

│

www.maximintegrated.com

Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN = 12V, CCCV = 0.022μF, RCCV = 5.1kΩ, VISET = VOSC = VDD = VCC, RFSET = 464kΩ, VPWMI = GND,

LEDs = 10 series x 4 parallel strings, TA = +25°C, unless otherwise noted.)

LINE TRANSIENT RESPONSE

(VIN = 12V→19V, BRIGHTNESS = 100%)

MAX17061A toc16

100s/div

VOUT

20V/div

1A/div

IFB1

20mA/div

VIN

10V/div

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

0mA

LINE TRANSIENT RESPONSE

(VIN = 19V→12V, BRIGHTNESS = 100%)

MAX17061A toc17

100s/div

VOUT

20V/div

1A/div

IFB1

20mA/div

VIN

10V/div

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

0mA

LED CURRENT BALANCE

vs. INPUT VOLTAGE

MAX17061A toc18

LED CURRENT BALANCE (%)

17 2014118

0.10

0.15

0.20

0.25

0.30

0.05

INPUT VOLTAGE (V)

MAX17061A 8-String White LED Driver with

SMBus for LCD Panel Applications

Maxim Integrated

│

www.maximintegrated.com

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.

DPWM

fR[ ]

=α× Ω +γ

MAX17061A 8-String White LED Driver with

SMBus for LCD Panel Applications

www.maximintegrated.com Maxim Integrated

│

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 sufcient copper connection to ensure

low thermal resistance. See the PCB Layout Guidelines section.

MAX17061A 8-String White LED Driver with

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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

VIN

7V TO 21V

LX2

FB2

FB3

FB4

FB5

FB6

FB7

FB8

10µH

0.1µF

1µF

4.7µF

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

61.9kΩ

2µF

2.21MΩ

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Figure 2. Control Circuit Block Diagram

IN UVLO

OSCILLATOR SLOPE

COMPENSATION

CLOCK

FB OVERVOLTAGE

COMPARATOR

ERROR

COMPARATOR

OUTPUT OVERVOLTAGE

COMPARATOR

VDD

LX1, 2

PGND1, 2

ERROR

AMPLIFIER

CURRENT SOURCE

FB1

GND

FB2

OV FAULT

CONTROL AND

DRIVER LOGIC

CURRENT SENSE

HVC FB6

FB5

FB4

FB3

FB2

LVC

3-LEVEL

COMPARATOR

FB7

FB8

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

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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

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

×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

ILEDMAX

ILED

D = 50%

D = tON

tON

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:

DPWM

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

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

< = 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

DEVICE

CONTROL

BRIGHTNESS

CONTROL

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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

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 denitions:

BIT FIELD DEFINITION DESCRIPTION

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

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 denitions:

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

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

Table 3. Vendor IDs

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 denitions:

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)

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 denitions:

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

IN(MIN)

OSC(MAX) OUT(MAX) OUT(MAX)

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 Rectier 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:

OUT_CCM(MAX) LIM OSC

0.5 D V



××

= −





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:

( )

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:

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

=×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

IN(MIN)

OSC(MAX) OUT(MAX) OUT(MAX)

RIPPLE

PEAK IN(DC,MAX)

2f V 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:

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)

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.

Rectier 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



= ×+





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.

MAX17061A 8-String White LED Driver with

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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*

FB4

N.C.

FB5

N.C.

FB6

FB3

PGND1

N.C.

LX1

LX2

SCL

1 2

4 5 6 7

2021 19 17 16 15

ISET

FB1

PWMO

PWMI

OSC

FB8

MAX17061A

GND PGND2

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 Conguration

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 specications 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

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│

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

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