MAX16814ATP/V+T - MAXIM INTEGRATED PRODUCTS

General Description

The MAX16814 high-efficiency, high-brightness LED (HB

LED) driver provides up to four integrated LED current-

sink channels. An integrated current-mode switching

DC-DC controller drives a DC-DC converter that provides

the necessary voltage to multiple strings of HB LEDs.

The MAX16814 accepts a wide 4.75V to 40V input volt-

age range and withstands direct automotive load-dump

events. The wide input range allows powering HB LEDs

for small to medium-sized LCD displays in automotive

and general lighting applications.

An internal current-mode switching DC-DC control-

ler supports the boost, coupled-inductor boost-buck,

or SEPIC topologies and operates in an adjustable

frequency range between 200kHz and 2MHz. It can

also be used for single-inductor boost-buck topology in

conjunction with the MAX15054 and an additional

MOSFET. The current-mode control with programma-

ble slope compensation provides fast response and

simplifies loop compensation. The MAX16814 also

features an adaptive output-voltage-control scheme that

minimizes the power dissipation in the LED current-sink

paths.

The MAX16814 consists of four identical linear current

source channels to drive four strings of HB LEDs. The

channel current is adjustable from 20mA to 150mA with

an accuracy of ±3% using an external resistor. The

external resistor sets all 4-channel currents to the same

value. The device allows connecting multiple channels

in parallel to achieve higher current per LED string. The

MAX16814 also features pulsed dimming control on all

four channels through a logic input (DIM). In addition,

the MAX16814A_ _ and MAX16814U_ _ include a unique

feature that allows a very short minimum pulse width as

low as 1µs.

The MAX16814 includes output overvoltage, open-

LED detection and protection, programmable shorted-

LED detection and protection, and overtemperature

protection. The device operates over the -40NC to

+125NC automotive temperature range. The MAX16814 is

available in 6.5mm x 4.4mm, 20-pin TSSOP, 4mm x 4mm,

20-pin TQFN and QFND packages.

Benets and Features

●Cost-Effective 4-Channel Linear LED Current Sinks

for Wide Range of LED Lighting Applications

• Drives One to Four LED Strings

• 4.75V to 40V Input Voltage Range

• Full-Scale LED Current Adjustable from 20mA

to 150mA

• 5000:1 PWM Dimming at 200Hz

• Less than 40µA Shutdown Current

●Minimal Component Count Saves Cost and Space

• Internal MOSFET for Each Channel

• Internal Current-Mode Switching DC-DC Controller

Supporting Boost, Coupled-Inductor Boost-Buck, or

SEPIC Topologies

• 200kHz to 2MHz Programmable Switching

Frequency for Optimizing Size vs. Efciency

• External Switching-Frequency Synchronization

●Protection Features and Wide Operating

Temperature Range improves Reliability

• Open-Drain Fault-Indicator Output

• Open-LED and LED-Short Detection and Protection

• Overtemperature Protection

• Available in Thermally Enhanced 20-Pin TQFN,

QFND, and TSSOP Packages

• Operation Over -40°C to +125°C Temperature Range

19-4722; Rev 11; 3/16

Applications

●Automotive Displays LED Backlights

●Automotive RCL, DRL, Front Position, and Fog Lights

●LCD TV and Desktop Display LED Backlights

●Architectural, Industrial, and Ambient Lighting

Typical Operating Circuit and Ordering Information appear

at end of data sheet.

MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

EVALUATION KIT AVAILABLE

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional opera-

tion 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 SGND ............................................................-0.3V to +45V

EN to SGND ...............................................-0.3V to (VIN + 0.3V)

PGND to SGND ....................................................-0.3V to +0.3V

LEDGND to SGND ...............................................-0.3V to +0.3V

OUT_ to LEDGND .................................................-0.3V to +45V

VCC to SGND .......... -0.3V to the lower of (VIN + 0.3V) and +6V

DRV, FLT, DIM, RSDT, OVP to SGND .....................-0.3V to +6V

CS, RT, COMP, SETI to SGND ................. -0.3V to (VCC + 0.3V)

NDRV to PGND .......................................-0.3V to (VDRV + 0.3V)

NDRV Peak Current (< 100ns) ............................................. Q3A

NDRV Continuous Current ............................................ Q100mA

OUT_ Continuous Current ............................................. Q175mA

VCC Short-Circuit Duration ........................................Continuous

Continuous Power Dissipation (TA = +70NC) (Note 1)

20-Pin TQFN (derate 25.6mW/NC above +70NC) ....... 2051mW

20-Pin Side-Wettable QFND

(derate 26.5mW/NC above +70NC) ............................2050mW

26-Pin TSSOP (derate 26.5mW/NC above +70NC) ..... 2122mW

Operating Temperature Range

MAX16814A_ _ .............................................. -40NC to +125NC

MAX16814BE_ _ ............................................. -40NC to +85NC

MAX16814U_ _and MAX16814BU_ _ ................0NC to +85NC

Junction Temperature .....................................................+150NC

Storage Temperature Range ............................ -65NC to +150NC

Lead Temperature (soldering, 10s) ................................+300NC

Soldering Temperature (reflow) ......................................+260NC

Electrical Characteristics

(VIN = VEN = 12V, RRT = 12.25kI, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VRSDT = VDIM

= VCC, VOVP = VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40NC to +125NC for MAX16814A_ _, TA = -40NC to +85NC for

MAX16814BE_ _, and TA = TJ = 0NC to +85NC for MAX16814U_ _ and MAX16814BU_ _, unless otherwise noted. Typical values are at

TA = +25NC.) (Note 2)

Absolute Maximum Ratings

Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer

board. For detailed information on package thermal considerations, refer to http://www.maximintegrated.com/thermal-tutorial.

Package Thermal Characteristics (Note 1)

20 TQFN/QFND

Junction-to-Ambient Thermal Resistance (BJA) ........ +39NC/W

Junction-to-Case Thermal Resistance (BJC) ............... +6NC/W

20 TSSOP

Junction-to-Ambient Thermal Resistance (BJA) ..... +37.7NC/W

Junction-to-Case Thermal Resistance (BJC) ............ +2.0NC/W

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Operating Voltage Range VIN 4.75 40 V

Active Supply Current IIN MAX16814A_ _ and MAX16814U_ _ 2.5 5 mA

MAX16814B_ _ _ only 2.75 5.5

Standby Supply Current VEN = 0V 15 40 µA

IN Undervoltage Lockout VIN rising 3.975 4.3 4.625 V

IN UVLO Hysteresis 170 mV

VCC REGULATOR

Regulator Output Voltage VCC 6.5V < VIN < 10V, 1mA < ILOAD < 50mA 4.75 5.0 5.25 V

10V < VIN < 40V, 1mA < ILOAD < 10mA

Dropout Voltage VIN - VCC, VIN = 4.75V, ILOAD = 50mA 200 500 mV

Short-Circuit Current Limit VCC shorted to SGND 100 mA

VCC Undervoltage Lockout

Threshold VCC rising 4 V

VCC UVLO Hysteresis 100 mV

RT OSCILLATOR

Switching Frequency Range fSW 200 2000 kHz

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Electrical Characteristics (continued)

(VIN = VEN = 12V, RRT = 12.25kI, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VRSDT = VDIM

= VCC, VOVP = VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40NC to +125NC for MAX16814A_ _, TA = -40NC to +85NC for

MAX16814BE_ _, and TA = TJ = 0NC to +85NC for MAX16814U_ _ and MAX16814BU_ _, unless otherwise noted. Typical values are at

TA = +25NC.) (Note 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Maximum Duty Cycle

fSW = 200kHz to 600kHz, MAX16814A_ _

and MAX16814U_ _ 85 89 93

fSW = 600kHz to 2000kHz, MAX16814A_ _

and MAX16814U_ _ 82 86 90

fSW = 200kHz to 600kHz, MAX16814B_ _ 90 94 98

fSW = 600kHz to 2000kHz, MAX16814B _ _ _ 86 90 94

Oscillator Frequency Accuracy

fSW = 200kHz to 2MHz, MAX16814A_ _

and MAX16814U_ _ -7.5 +7.5 %

fSW = 200kHz to 2MHz, MAX16814B_ _ _ -7 +7

Sync Rising Threshold 4 V

Minimum Sync Frequency 1.1fSW Hz

PWM COMPARATOR

PWM Comparator Leading-Edge

Blanking Time 60 ns

PWM to NDRV Propagation Delay Including leading-edge blanking time 90 ns

SLOPE COMPENSATION

Peak Slope Compensation

Current Ramp Magnitude

Current ramp added to the CS input,

MAX16814A_ _ only 44 49 54

µA x fSW

Current ramp added to the CS input,

MAX16814U_ _ and MAX16814B_ _ _ 45 50 55

CS LIMIT COMPARATOR

Current-Limit Threshold (Note 3) 396 416 437 mV

CS Limit Comparator to NDRV

Propagation Delay

10mV overdrive, excluding leading-edge

blanking time 10 ns

ERROR AMPLIFIER

OUT_ Regulation Voltage 1 V

Transconductance gM340 600 880 µS

No-Load Gain (Note 4) 75 dB

COMP Sink Current VOUT_ = 5V, VCOMP = 2.5V 160 375 800 µA

COMP Source Current VOUT_ = 0V, VCOMP = 2.5V 160 375 800 µA

MOSFET DRIVER

NDRV On-Resistance ISINK = 100mA (nMOS) 0.9 ω

ISOURCE = 100mA (pMOS) 1.1

Peak Sink Current VNDRV = 5V 2.0 A

Peak Source Current VNDRV = 0V 2.0 A

Rise Time CLOAD = 1nF 6 ns

Fall Time CLOAD = 1nF 6 ns

LED CURRENT SOURCES

OUT_ Current-Sink Range VOUT_ = VREF 20 150 mA

Channel-to-Channel Matching IOUT_ = 100mA ±2 %

IOUT_ = 100mA, all channels on ±1.5

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Note 2: All MAX16814A_ _ are 100% tested at TA = +125NC, while all MAX16814U_ _ and MAX16814B _ _ _ are 100% tested at

TA = +25°C. All limits overtemperature are guaranteed by design, not production tested.

Note 3: CS threshold includes slope-compensation ramp magnitude.

Note 4: Gain = δVCOMP/δVCS, 0.05V < VCS < 0.15V.

Electrical Characteristics (continued)

(VIN = VEN = 12V, RRT = 12.25kI, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VRSDT = VDIM

= VCC, VOVP = VCS = VLEDGND = VPGND = VSGND = 0V, TA = TJ = -40NC to +125NC for MAX16814A_ _, TA = -40NC to +85NC for

MAX16814BE_ _, and TA = TJ = 0NC to +85NC for MAX16814U_ _ and MAX16814BU_ _, unless otherwise noted. Typical values are at

TA = +25NC.) (Note 2)

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

Output Current Accuracy

IOUT_ =

100mA

TA = +125°C, MAX16814A_ _

only ±3

TA = -40°C to +125°C,

MAX16814A_ _ only ±5

IOUT_ =

50mA to

150mA

TA = +25°C, MAX16814U_ _ and

MAX16814B_ _ _ ±2.75

TA = 0°C to +85°C, MAX16814U_

_ and MAX16814BU _ _ ±4

TA = -40°C to +85°C for

MAX16814BE _ _ ±4

OUT_ Leakage Current VDIM = 0V, VOUT_ = 40V 1 µA

LOGIC INPUTS/OUTPUTS

EN Reference Voltage

VEN rising, MAX16814A_ _ only 1.125 1.23 1.335

VEN rising, MAX16814U_ _ and

MAX16814B_ _ _ 1.144 1.23 1.316

EN Hysteresis 50 mV

EN Input Current VEN = 40V ±600 nA

DIM Input High Voltage 2.1 V

DIM Input Low Voltage 0.8 V

DIM Hysteresis 250 mV

DIM Input Current ±2 µA

DIM to LED Turn-On Delay DIM rising edge to 10% rise in IOUT_ 100 ns

DIM to LED Turn-Off Delay DIM falling edge to 10% fall in IOUT_100 ns

IOUT_ Rise and Fall Times 200 ns

FLT Output Low Voltage VIN = 4.75V and ISINK = 5mA 0.4 V

FLT Output Leakage Current VFLT = 5.5V 1.0 µA

LED Short Detection Threshold Gain = 3V 1.75 2.0 2.25 V

Short Detection Comparator Delay 6.5 µs

RSDT Leakage Current ±600 nA

OVP Trip Threshold Output rising 1.19 1.228 1.266 V

OVP Hysteresis 70 mV

OVP Leakage Current VOVP = 1.25V ±200 nA

Thermal-Shutdown Threshold Temperature rising 165 °C

Thermal-Shutdown Hysteresis 15 °C

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Typical Operating Characteristics

(VIN = VEN = 12V, fSW = 300kHz, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VOVP = VCS =

VLEDGND = VDIM = VPGND = VSGND = 0V, load = 4 strings of 7 white LEDs, TA = +25NC, unless otherwise noted.)

SUPPLY CURRENT

vs. SWITCHING FREQUENCY

MAX16814 toc03

fSW (kHz)

(mA)

1600140012001000800600400

3.2

3.4

3.6

3.8

4.0

4.2

4.4

3.0

200 1800 2000

CNDRV = 13pF

VSETI vs. PROGRAMMED CURRENT

MAX16814 toc06

LED STRING CURRENT (mA)

VSETI (V)

124987246

1.229

1.230

1.231

1.232

1.233

1.234

1.228

20 150

SWITCHING WAVEFORM AT 5kHz

(50% DUTY CYCLE) DIMMING

MAX16814 toc01

IOUT1

100mA/div

VOUT

10V/div

VLX

10V/div

40Fs/div

FIGURE 2

SWITCHING FREQUENCY

vs. TEMPERATURE

MAX16814 toc04

TEMPERATURE (NC)

SWITCHING FREQUENCY (kHz)

1007525 500-25

292

294

296

298

300

302

304

306

308

310

290

-50 125

EN THRESHOLD VOLTAGE

vs. TEMPERATURE

MAX16814 toc07

TEMPERATURE (NC)

EN THRESHOLD VOLTAGE (V)

1007550250-25

1.15

1.20

1.25

1.30

1.10

-50 125

VEN RISING

VEN FALLING

SUPPLY CURRENT vs. SUPPLY VOLTAGE

MAX16814 toc02

VIN (V)

IIN (mA)

40353025201510

2.6

2.8

3.0

3.2

3.4

3.6

3.8

2.4

CNDRV = 13pF TA = +125NC

TA = +25NC

TA = -40NC

VSETI vs. TEMPERATURE

MAX16814 toc05

TEMPERATURE (NC)

SETI

(V)

1007550250-25

1.224

1.228

1.232

1.236

1.240

1.220

-50 125

EN LEAKAGE CURRENT

vs. TEMPERATURE

MAX16814 toc08

TEMPERATURE (NC)

EN LEAKAGE CURRENT (nA)

1007550250-25

120

150

-50 125

VEN = 2.5V

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Typical Operating Characteristics (continued)

(VIN = VEN = 12V, fSW = 300kHz, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VOVP = VCS =

VLEDGND = VDIM = VPGND = VSGND = 0V, load =4 strings of 7 white LEDs, TA = +25NC, unless otherwise noted.)

VCC LINE REGULATION

MAX16814 toc09

VIN (V)

VCC (V)

353025201510

5.00

5.02

5.04

5.06

5.08

4.96

4.98

TA = +125NC

TA = +25NC

TA = -40NC

VCC LOAD REGULATION

MAX16814 toc10

IVCC (mA)

VCC (V)

604020

4.92

4.94

4.96

4.98

5.00

5.02

5.04

5.06

5.08

5.10

4.90

TA = -40NC

TA = +25NC

TA = +125NC

SWITCHING FREQUENCY vs. 1/RT

MAX16814 toc11

1/RT (mS)

SWITCHING FREQUENCY (MHz)

0.260.220.14 0.180.100.06

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

0.02 0.30

STARTUP WAVEFORM WITH

DIM ON PULSE WIDTH < tSW

MAX16814 toc12

IOUT_

100mA/div

VIN

20V/div

VDIM

5V/div

VLED

20V/div

40ms/div

STARTUP WAVEFORM WITH DIM

ON PULSE WIDTH = 10tSW

MAX16814 toc13

IOUT1

100mA/div

VLED

10V/div

VIN

20V/div

VDIM

5V/div

40ms/div

FIGURE 2

STARTUP WAVEFORM WITH DIM

CONTINUOUSLY ON

MAX16814 toc14

IOUT1

100mA/div

VLED

10V/div

VIN

20V/div

VDIM

5V/div

40ms/div

FIGURE 2

MOSFET DRIVER ON-RESISTANCE

vs. TEMPERATURE

MAX16814 toc15

TEMPERATURE (NC)

ON-RESISTANCE (I)

1007550250-25

0.7

0.9

1.1

1.3

1.5

0.5

-50 125

pMOS

nMOS

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Typical Operating Characteristics (continued)

(VIN = VEN = 12V, fSW = 300kHz, RSETI = 15kI, CVCC = 1FF, VCC = VDRV, NDRV = COMP = OUT_ = unconnected, VOVP = VCS =

VLEDGND = VDIM = VPGND = VSGND = 0V, load = 4 strings of 7 white LEDs, TA = +25NC, unless otherwise noted.)

LED CURRENT SWITCHING WITH DIM

AT 5kHz AND 50% DUTY CYCLE

MAX16814 toc16

IOUT3

100mA/div

IOUT4

100mA/div

IOUT1

100mA/div

IOUT2

100mA/div

100Fs/div

FIGURE 2

LED CURRENT RISING AND FALLING

WAVEFORM

MAX16814 toc17

VDIM

5V/div

ILED

50mA/div

4Fs/div

FIGURE 2

OUT_ LEAKAGE CURRENT

vs. TEMPERATURE

MAX16814 toc20

TEMPERATURE (NC)

OUT_ LEAKAGE CURRENT (nA)

100

0.1

1007550250-25-50 125

VDIM = 0V

VOUT = 40V

OUT_ CURRENT vs. 1/RSETI

MAX16814 toc18

1/RSETI (mS)

OUT_

(mA)

0.0850.0700.0550.0400.025

100

120

140

160

0.010 0.100

OVP LEAKAGE CURRENT

vs. TEMPERATURE

MAX16814 toc21

TEMPERATURE (NC)

OVP LEAKAGE CURRENT (nA)

1007525 500-25

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

-50 125

VOVP = 1.25V

COMP LEAKAGE CURRENT

vs. TEMPERATURE

MAX16814 toc19

TEMPERATURE (NC)

COMP LEAKAGE CURRENT (nA)

1007550250-25

0.2

0.4

0.6

0.8

1.0

-50 125

VDIM = 0V

VCOMP = 4.5V

VCOMP = 0.5V

RSDT LEAKAGE CURRENT

vs. TEMPERATURE

MAX16814 toc22

TEMPERATURE (NC)

RSDT LEAKAGE CURRENT (nA)

1007550250-25

100

150

200

250

-50 125

VRSDT = 0.5V

VRSDT = 2.5V

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Pin Description

Pin Congurations

NAME FUNCTION

TQFN/

QFND TSSOP

1 4 IN Bias Supply Input. Connect a 4.75V to 40V supply to IN. Bypass IN to SGND with a ceramic

capacitor.

2 5 EN Enable Input. Connect EN to logic-low to shut down the device. Connect EN to logic-high or IN

for normal operation. The EN logic threshold is internally set to 1.23V.

3 6 COMP Switching Converter Compensation Input. Connect the compensation network from COMP to

SGND for current-mode control (see the Feedback Compensation section).

4 7 RT

Oscillator Timing Resistor Connection. Connect a timing resistor (RT) from RT to SGND to program

the switching frequency according to the formula RT = 7.350 x 109/fsw (for the MAX16814A_ _

and the MAX16814U_ _) or to the formula RT = 7.72 x 109/fsw (for the MAX16814B_ _ _). Apply an

AC-coupled external clock at RT to synchronize the switching frequency with an external clock.

5 8 FLT Open-Drain Fault Output. FLT asserts low when an open LED, short LED, or thermal shutdown

is detected. Connect a 10kω pullup resistor from FLT to VCC.

6 9 OVP Overvoltage-Threshold-Adjust Input. Connect a resistor-divider from the switching converter

output to OVP and SGND. The OVP comparator reference is internally set to 1.23V.

7 10 SETI LED Current-Adjust Input. Connect a resistor (RSETI) from SETI to SGND to set the current

through each LED string (ILED) according to the formula ILED = 1500/RSETI.

8 11 RSDT

LED Short Detection Threshold Adjust Input. Connect a resistive divider from VCC to RSDT and

SGND to program the LED short detection threshold. Connect RSDT directly to VCC to disable

LED short detection. The LED short detection comparator is internally referenced to 2V.

9 12 SGND Signal Ground. SGND is the current return path connection for the low-noise analog signals.

Connect SGND, LEDGND, and PGND at a single point.

PGND

OUT4

OUT3IN

VCC

DRV

NDRV

TOP VIEW

MAX16814

LEDGND

OUT2

OUT1RT

COMP

138 DIMFLT

129 SGNDOVP

1110 RSDTSETI

EP*

*EXPOSED PAD.

TSSOP

FLT

OUT3

OUT2

OUT1

OUT4

1 2

NDRV

4 5

15 14 12 11

DRV

VCC

SGND

RSDT

SETI

OVP

MAX16814

COMP LEDGND

PGND

EP*

10 DIM

TQFN/QFND

TOP VIEW

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Pin Description (continued)

NAME FUNCTION

TQFN/

QFND TSSOP

10 13 DIM Digital PWM Dimming Input. Apply a PWM signal to DIM for LED dimming control. Connect DIM

to VCC if dimming control is not used.

11 14 OUT1

LED String Cathode Connection 1. OUT1 is the open-drain output of the linear current sink that

controls the current through the LED string connected to OUT1. OUT1 sinks up to 150mA. If

unused, connect OUT1 to LEDGND.

12 15 OUT2

LED String Cathode Connection 2. OUT2 is the open-drain output of the linear current sink that

controls the current through the LED string connected to OUT2. OUT2 sinks up to 150mA. If

unused, connect OUT2 to LEDGND.

13 16 LEDGND LED Ground. LEDGND is the return path connection for the linear current sinks. Connect

SGND, LEDGND, and PGND at a single point.

14 17 OUT3

LED String Cathode Connection 3. OUT3 is the open-drain output of the linear current sink that

controls the current through the LED string connected to OUT3. OUT3 sinks up to 150mA. If

unused, connect OUT3 to LEDGND.

15 18 OUT4

LED String Cathode Connection 4. OUT4 is the open-drain output of the linear current sink that

controls the current through the LED string connected to OUT4. OUT4 sinks up to 150mA. If

unused, connect OUT4 to LEDGND.

16 19 CS

Current-Sense Input. CS is the current-sense input for the switching regulator. A sense resistor

connected from the source of the external power MOSFET to PGND sets the switching current

limit. A resistor connected between the source of the power MOSFET and CS sets the slope

compensation ramp rate (see the Slope Compensation section).

17 20 PGND Power Ground. PGND is the switching current return path connection. Connect SGND,

LEDGND, and PGND at a single point.

18 1 NDRV Switching n-MOSFET Gate-Driver Output. Connect NDRV to the gate of the external switching

power MOSFET.

19 2 DRV

MOSFET Gate-Driver Supply Input. Connect a resistor between VCC and DRV to power the

MOSFET driver with the internal 5V regulator. Bypass DRV to PGND with a minimum of 0.1µF

ceramic capacitor.

20 3 VCC 5V Regulator Output. Bypass VCC to SGND with a minimum of 1µF ceramic capacitor as close

as possible to the device.

— — EP Exposed Pad. Connect EP to a large-area contiguous copper ground plane for effective power

dissipation. Do not use as the main IC ground connection. EP must be connected to SGND.

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Figure 1. Simplified Functional Diagram

FAULT FLAG

LOGIC

TSHDN

( = 50FA x fsw)

0.425V

OVP

COMP

ILIM

MAX16814

CS BLANKING

TSHDN

PWM

LOGIC

DRV

CLK

2.5V

NDRV

PGND

THERMAL

SHUTDOWN

SOFT-START

100ms

BANDGAP

VREF

SS_REF SS_DONE

UVLO

5V LDO

REGULATOR

SLOPE

COMPENSATION

RAMP/RT OSC

LOGIC

(REF/FB

SELECTOR)

SHORT LED

DETECTOR

RSDTFLT

POKD

VREF

LEDGND

OUT_

DIM

OPEN-LED

DETECTOR

LOGIC

MIN STRING

VOLTAGE

UNUSED

STRING

DETECTOR

SHDN

TSHDN

COMP

VCC

POKD

POK

VBG = 1.235V

VBG

SGND

SETIOVP

SHDN

REF

SGND

1.23V

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MAX16814 Integrated, 4-Channel, High-Brightness LED

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Figure 2. Circuit Used for Typical Operating Characteristics

OUT2

OUT1

IN NDRV CS OVP

PGND LEDGND

OUT3

OUT4

VDRV

VCC

SETI

FLT

RSDT

VIN

C5 C1

SGND

MAX16814

7 HBLEDS

PER STRING

C2 C7

RSETI

RCS

RSCOMP

VCC

RCOMP

CCOMP

DIM

COMP

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MAX16814 Integrated, 4-Channel, High-Brightness LED

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Detailed Description

The MAX16814 high-efficiency HB LED driver

integrates all the necessary features to implement a

high-performance backlight driver to power LEDs in

small to medium-sized displays for automotive as well

as general applications. The device provides load-dump

voltage protection up to 40V in automotive applications.

The MAX16814 incorporates two major blocks: a DC-DC

controller with peak current-mode control to implement

a boost, coupled-inductor boost-buck, or a SEPIC-type

switched-mode power supply and a 4-channel LED

driver with 20mA to 150mA constant current-sink capa-

bility per channel. Figure 1 is the simplified functional

diagram and Figure 2 shows the circuit used for typical

operating characteristics.

The MAX16814 features a constant-frequency peak

current-mode control with programmable slope

compensation to control the duty cycle of the PWM

controller. The high-current FET driver can provide up

to 2A of current to the external n-channel MOSFET.

The DC-DC converter implemented using the controller

generates the required supply voltage for the LED

strings from a wide input supply range. Connect LED

strings from the DC-DC converter output to the 4-channel

constant current-sink drivers that control the current

through the LED strings. A single resistor connected

from the SETI input to ground adjusts the forward current

through all four LED strings.

The MAX16814 features adaptive voltage control that

adjusts the converter output voltage depending on the

forward voltage of the LED strings. This feature mini-

mizes the voltage drop across the constant current-sink

drivers and reduces power dissipation in the device. A

logic input (EN) shuts down the device when pulled low.

The device includes an internal 5V LDO capable of pow-

ering additional external circuitry.

All the versions of the MAX16814 include PWM dimming.

The MAX16814A_ and the MAX16814U_ versions, in par-

ticular, provide very wide (5000:1) PWM dimming range

where a dimming pulse as narrow as 1µs is possible at

a 200Hz dimming frequency. This is made possible by

a unique feature that detects short PWM dimming input

pulses and adjusts the converter feedback accordingly.

Advanced features include detection and string-

disconnect for open-LED strings, partial or fully shorted

strings, and unused strings. Overvoltage protection

clamps the converter output voltage to the programmed

OVP threshold in the event of an open-LED condi-

tion. Shorted LED string detection and overvoltage

protection thresholds are programmable using RSDT

and OVP inputs, respectively. An open-drain FLT signal

asserts to indicate open-LED, shorted-LED, and over-

temperature conditions. Disable individual current-sink

channels by connecting the corresponding OUT_ to

LEDGND. In this case, FLT does not assert indicating

an open-LED condition for the disabled channel. The

device also features an overtemperature protection that

shuts down the controller if the die temperature exceeds

+165NC.

Current-Mode DC-DC Controller

The peak current-mode controller allows boost, coupled-

inductor buck-boost, or SEPIC-type converters to generate

the required bias voltage for the LED strings. The switch-

ing frequency can be programmed over the 200kHz to

2MHz range using a resistor connected from RT to SGND.

Programmable slope compensation is available to com-

pensate for subharmonic oscillations that occur at above

50% duty cycles in continuous-conduction mode.

The external MOSFET is turned on at the beginning of

every switching cycle. The inductor current ramps up

linearly until it is turned off at the peak current level set by

the feedback loop. The peak inductor current is sensed

from the voltage across the current-sense resistor (RCS)

connected from the source of the external MOSFET to

PGND. The MAX16814 features leading-edge blanking to

suppress the external MOSFET switching noise. A PWM

comparator compares the current-sense voltage plus the

slope-compensation signal with the output of the trans-

conductance error amplifier. The controller turns off the

external MOSFET when the voltage at CS exceeds the

error amplifier’s output voltage. This process repeats every

switching cycle to achieve peak current-mode control.

Error Amplier

The internal error amplifier compares an internal feed-

back (FB) with an internal reference (REF) and regulates

its output to adjust the inductor current. An internal mini-

mum string detector measures the minimum current-sink

voltage with respect to SGND out of the four constant-

current-sink channels. During normal operation, this

minimum OUT_ voltage is regulated to 1V through

feedback. The error amplifier takes 1V as the REF

and the minimum OUT_ voltage as the FB input. The

amplified error at the COMP output controls the inductor

peak current to regulate the minimum OUT_ voltage at

1V. The resulting DC-DC converter output voltage is the

highest LED string voltage plus 1V.

The converter stops switching when the LED strings are

turned off during PWM dimming. The error amplifier is

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MAX16814 Integrated, 4-Channel, High-Brightness LED

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disconnected from the COMP output to retain the com-

pensation capacitor charge. This allows the converter

to settle to steady-state level almost immediately when

the LED strings are turned on again. This unique feature

provides fast dimming response, without having to use

large output capacitors.

For the MAX16814A_ _ and the MAX16814U_ _, if the

PWM dimming on-pulse is less than or equal to five

switching cycles, the feedback controls the voltage on

OVP so that the converter output voltage is regulated at

95% of the OVP threshold. This mode ensures that narrow

PWM dimming pulses are not affected by the response

time of the converter. During this mode, the error amplifier

remains connected to the COMP output continuously and

the DC-DC converter continues switching.

Undervoltage Lockout (UVLO)

The MAX16814 features two undervoltage lockouts that

monitor the input voltage at IN and the output of the inter-

nal LDO regulator at VCC. The device turns on after both

VIN and VCC exceed their respective UVLO thresholds.

The UVLO threshold at IN is 4.3V when VIN is rising and

4.15V when VIN is falling. The UVLO threshold at VCC is

4V when VCC is rising and 3.9V when VCC is falling.

Enable

EN is a logic input that completely shuts down the

device when connected to logic-low, reducing the

current consumption of the device to less than 40FA.

The logic threshold at EN is 1.23V (typ). The voltage

at EN must exceed 1.23V before any operation can

commence. There is a 50mV hysteresis on EN. The EN

input also allows programming the supply input UVLO

threshold using an external voltage-divider to sense the

input voltage as shown below.

Use the following equation to calculate the value of R1

and R2 in Figure 3:

UVLO

R1 - 1 R2

1.23V



= ×





where VUVLO is the desired undervoltage lockout level

and 1.23V is the EN input reference. Connect EN to IN

if not used.

Soft-Start

The MAX16814 provides soft-start with internally set timing. At

power-up, the MAX16814 enters soft-start once unused LED

strings are detected and disconnected (see the Open-LED

Management and Overvoltage Protection section). During

soft-start, the DC-DC converter output ramps towards

95% of the OVP voltage and uses feedback from the OVP

input. Soft-start terminates when the minimum current-sink

voltage reaches 1V or when the converter output reaches

95% OVP. The typical soft-start period is 100ms. The 1V

minimum OUT_ voltage is detected only when the LED

strings are enabled by PWM dimming. Connect OVP to

the boost converter output through a resistive divider

network (see the Typical Operating Circuit).

When there is an open-LED condition, the converter output

hits the OVP threshold. After the OVP is triggered, open-

LED strings are disconnected and, at the beginning of the

dimming PWM pulse, control is transferred to the adaptive

voltage control. The converter output discharges to a level

where the new minimum OUT_ voltage is 1V.

Oscillator Frequency/External Synchronization

The internal oscillator frequency is programmable

between 200kHz and 2MHz using a resistor (RT) con-

nected from the RT input to SGND. Use the equation

below to calculate the value of RT for the desired switch-

ing frequency, fSW.

TSW

7.35 10 Hz

(for the MAX16814A_ _ and the MAX16814U_ _).

TSW

7.72 10

(for the MAX16814B_ _ _).

Synchronize the oscillator with an external clock by

AC-coupling the external clock to the RT input. The

capacitor used for the AC-coupling should satisfy the

following relation:

( )

-3

SYNC

9.862

C -0.144 10 F



≤ ×µ





where RT is in Ω.

Figure 3. Setting the MAX16814 Undervoltage Lockout

Threshold

1.23V

VIN

MAX16814

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MAX16814 Integrated, 4-Channel, High-Brightness LED

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The pulse width for the synchronization pulse should

satisfy the following relations:

( )

PW S

CLK

PW SS

CLK

PW CI CLK

V 0.5

0.8 V V 3.4

t t 1.05 t



− +>





< −×

where tPW is the synchronization source pulse width,

tCLK is the synchronization clock time period, tCI is the

programmed clock period, and VS is the synchronization

pulse voltage level.

5V LDO Regulator (VCC)

The internal LDO regulator converts the input voltage

at IN to a 5V output voltage at VCC. The LDO regulator

supplies up to 50mA current to provide power to internal

control circuitry and the gate driver. Connect a resistor

between VCC and DRV to power the gate-drive circuitry;

the recommended value is 4.7I. Bypass DRV with a

capacitor to PGND. The external resistor and bypass

capacitor provide noise filtering. Bypass VCC to SGND

with a minimum of 1FF ceramic capacitor as close to the

device as possible.

PWM MOSFET Driver

The NDRV output is a push-pull output with the on-resis-

tance of the pMOS typically 1.1I and the on-resistance

of the nMOS typically 0.9I. NDRV swings from PGND to

DRV to drive an external n-channel MOSFET. The driver

typically sources 2.0A and sinks 2.0A allowing for fast

turn-on and turn-off of high gate-charge MOSFETs.

The power dissipation in the MAX16814 is mainly a

function of the average current sourced to drive the

external MOSFET (IDRV) if there are no additional loads

on VCC. IDRV depends on the total gate charge (QG)

and operating frequency of the converter. Connect DRV

to VCC with a 4.7I resistor to power the gate driver with

the internal 5V regulator.

LED Current Control

The MAX16814 features four identical constant-current

sources used to drive multiple HB LED strings. The

current through each one of the four channels is adjust-

able between 20mA and 150mA using an external

resistor (RSETI) connected between SETI and SGND.

Select RSETI using the following formula:

SETI OUT_

R 1500 I=

where IOUT_ is the desired output current for each of the

four channels.

If more than 150mA is required in an LED string, use two

or more of the current source outputs (OUT_) connected

together to drive the string as shown in Figure 4.

LED Dimming Control

The MAX16814 features LED brightness control using an

external PWM signal applied at DIM. A logic-high signal

on the DIM input enables all four LED current sources

and a logic-low signal disables them.

For the MAX16814A_ _ and the MAX16814U_ _, the duty

cycle of the PWM signal applied to DIM also controls

the DC-DC converter’s output voltage. If the turn-on

duration of the PWM signal is less than or equal to 5

oscillator clock cycles (DIM pulse width decreasing) then

the boost converter regulates its output based on feed-

back from the OVP input. During this mode, the converter

output voltage is regulated to 95% of the OVP threshold

voltage. If the turn-on duration of the PWM signal is

greater than or equal to 6 oscillator clock cycles (DIM

pulse width increasing), then the converter regulates its

output so that the minimum voltage at OUT_ is 1V.

When the DIM signal crosses the 5 or 6 oscillator clock-

cycle boundary, the control loop of the MAX16814

experiences a discontinuity due to an internal mode

transition, which can cause flickering (the boost output

voltage changes, as described in previous paragraph).

To avoid flicker, the following is recommended:

●Avoid crossing the 5 or 6 oscillator clock-cycle

boundary.

Figure 4. Configuration for Higher LED String Current

OUT1

40mA TO 300mA

PER STRING

BOOST CONVERTER

OUTPUT

MAX16814 OUT2

OUT3

OUT4

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MAX16814 Integrated, 4-Channel, High-Brightness LED

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●Do not set the OVP level higher than 3V

above the maximum LED operating voltage.

●Optimize the compensation components so

that recovery is as fast as possible. If the loop

phase margin is less than 45°, the output voltage

may ring during the 5 or 6 oscillator clock-cycle

boundary crossing, which can contribute to flicker.

Fault Protections

Fault protections in the MAX16814 include cycle-

by-cycle current limiting using the PWM controller,

DC-DC converter output overvoltage protection, open-

LED detection, short LED detection and protection, and

overtemperature shutdown. An open-drain LED fault

flag output (FLT) goes low when an open-LED string

is detected, a shorted LED string is detected, and

during thermal shutdown. FLT is cleared when the fault

condition is removed during thermal shutdown and

shorted LEDs. FLT is latched low for an open-LED

condition and can be reset by cycling power or toggling

the EN pin. The thermal shutdown threshold is +165NC

and has 15NC hysteresis.

Open-LED Management and

Overvoltage Protection

On power-up, the MAX16814 detects and disconnects

any unused current-sink channels before entering

soft-start. Disable the unused current-sink channels

by connecting the corresponding OUT_ to LEDGND.

This avoids asserting the FLT output for the unused

channels. After soft-start, the MAX16814 detects open

LED and disconnects any strings with an open LED from

the internal minimum OUT_ voltage detector. This keeps

the DC-DC converter output voltage within safe limits

and maintains high efficiency. During normal operation,

the DC-DC converter output regulation loop uses the

minimum OUT_ voltage as the feedback input. If any

LED string is open, the voltage at the opened OUT_ goes

to VLEDGND. The DC-DC converter output voltage then

increases to the overvoltage protection threshold set by

the voltage-divider network connected between the con-

verter output, OVP input, SGND. The overvoltage protec-

tion threshold at the DC-DC converter output (VOVP) is

determined using the following formula:

(see the Typical Operating Circuit)

OVP R1

V 1.23 1



= ×+





where 1.23V (typ) is the OVP threshold. Select R1 and

R2 such that the voltage at OUT_ does not exceed

the absolute maximum rating. As soon as the DC-DC

converter output reaches the overvoltage

protection threshold, the PWM controller is switched off,

setting NDRV low. Any current-sink output with VOUT_

< 300mV (typ) is disconnected from the minimum voltage

detector.

Connect the OUT_ of all channels without LED

connections to LEDGND before power-up to avoid OVP

triggering at startup. When an open-LED overvoltage

condition occurs, FLT is latched low.

Short-LED Detection

The MAX16814 checks for shorted LEDs at each rising

edge of DIM. An LED short is detected at OUT_ if the fol-

lowing condition is met:

VOUT_ > VMINSTR + 3 x VRSDT

where VOUT_ is the voltage at OUT_, VMINSTR is

the minimum current-sink voltage, and VRSDT is the

programmable LED short detection threshold set at

the RSDT input. Adjust VRSDT using a voltage-divider

resistive network connected at the VCC output, RSDT

input, and SGND.

Once a short is detected on any of the strings, the LED

strings with the short are disconnected and the FLT

output flag asserts until the device detects that the shorts

are removed on any of the following rising edges of DIM.

Connect RSDT directly to VCC to always disable LED

short detection.

Applications Information

DC-DC Converter

Three different converter topologies are possible with

the DC-DC controller in the MAX16814, which has

the ground-referenced outputs necessary to use the

constant current-sink drivers. If the LED string forward

voltage is always more than the input supply voltage

range, use the boost converter topology. If the LED string

forward voltage falls within the supply voltage range, use

the boost-buck converter topology. Boost-buck topology

is implemented using either a conventional SEPIC con-

figuration or a coupled-inductor boost-buck configura-

tion. The latter is basically a flyback converter with 1:1

turns ratio. 1:1 coupled inductors are available with tight

coupling suitable for this application. Figure 6 shows

the coupled-inductor boost-buck configuration. It is also

possible to implement a single inductor boost-buck con-

verter using the MAX15054 high-side FET driver.

The boost converter topology provides the highest effi-

ciency among the above mentioned topologies. The

coupled-inductor boost-buck topology has the advan-

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tage of not using a coupling capacitor over the SEPIC

configuration. Also, the feedback loop compensation for

SEPIC becomes complex if the coupling capacitor is not

large enough. A coupled-inductor boost-buck is not suit-

able for cases where the coupled-inductor windings are

not tightly coupled. Considerable leakage inductance

requires additional snubber components and degrades

the efficiency.

Power-Circuit Design

First select a converter topology based on the previous

factors. Determine the required input-supply voltage

range, the maximum voltage needed to drive the LED

strings including the minimum 1V across the constant

LED current sink (VLED), and the total output current

needed to drive the LED strings (ILED) as follows:

LED STRING STRING

II N

= ×

where ISTRING is the LED current per string in amperes

and NSTRING is the number of strings used.

Calculate the maximum duty cycle (DMAX) using the

following equations:

For boost configuration:

LED D1 IN_MIN

MAX LED D1 DS

(V V V )

D(V V V 0.3V)

+−

=+− −

For SEPIC and coupled-inductor boost-buck configura-

tions:

LED D1

MAX IN_MIN DS LED D1

(V V )

D(V V 0.3V V V )

=−− + +

where VD1 is the forward drop of the rectifier diode in

volts (approximately 0.6V), VIN_MIN is the minimum input

supply voltage in volts, and VDS is the drain-to-source

voltage of the external MOSFET in volts when it is on,

and 0.3V is the peak current-sense voltage. Initially, use

an approximate value of 0.2V for VDS to calculate DMAX.

Calculate a more accurate value of DMAX after the power

MOSFET is selected based on the maximum inductor

current. Select the switching frequency (fSW) depending

on the space, noise, and efficiency constraints.

Inductor Selection

Boost and Coupled-Inductor Boost-Buck

Congurations

In all the three converter configurations, the average

inductor current varies with the line voltage and the

maximum average current occurs at the lowest line

voltage. For the boost converter, the average inductor

current is equal to the input current. Select the maxi-

mum peak-to-peak ripple on the inductor current (DIL).

The recommended peak-to-peak ripple is 60% of the

average inductor current.

Use the following equations to calculate the maximum

average inductor current (ILAVG) and peak inductor

current (ILP) in amperes:

LED

AVG MAX

IL 1D

=−

Allowing the peak-to-peak inductor ripple DIL to be

+30% of the average inductor current:

AVG

IL IL 0.3 2∆= × ×

and:

P AVG IL

IL IL 2

∆

= +

Calculate the minimum inductance value, LMIN, in

henries with the inductor current ripple set to the maxi-

mum value:

MIN DS MAX

MIN SW

(VIN V 0.3V) D

Lf IL

−− ×

=×∆

where 0.3V is the peak current-sense voltage. Choose

an inductor that has a minimum inductance greater than

the calculated LMIN and current rating greater than ILP.

The recommended saturation current limit of the selected

inductor is 10% higher than the inductor peak current

for boost configuration. For the coupled-inductor boost-

buck, the saturation limit of the inductor with only one

winding conducting should be 10% higher than ILP.

SEPIC Conguration

Power circuit design for the SEPIC configuration is very

similar to a conventional boost-buck design with the

output voltage referenced to the input supply voltage.

For SEPIC, the output is referenced to ground and the

inductor is split into two parts (see Figure 5 for the SEPIC

configuration). One of the inductors (L2) takes LED

current as the average current and the other (L1) takes

input current as the average current.

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Use the following equations to calculate the average

inductor currents (IL1AVG, IL2AVG) and peak inductor

currents (IL1P, IL2P) in amperes:

LED MAX

AVG MAX

I D 1.1

IL1 1D

××

=−

The factor 1.1 provides a 10% margin to account for the

converter losses:

AVG LED

IL2 I=

Assuming the peak-to-peak inductor ripple DIL is Q30%

of the average inductor current:

AVG

IL1 IL1 0.3 2∆= × ×

and:

P AVG IL1

IL1 IL1 2

∆

= +

AVG

IL2 IL2 0.3 2∆= ××

and:

P AVG IL2

IL2 IL2 2

∆

= +

Calculate the minimum inductance values L1MIN and

L2MIN in henries with the inductor current ripples set to

the maximum value as follows:

MIN DS MAX

MIN SW

MIN DS MAX

MIN SW

(VIN V 0.3V) D

L1 f IL1

(VIN V 0.3V) D

L2 f IL2

−− ×

=×∆

−− ×

=×∆

where 0.3V is the peak current-sense voltage. Choose

inductors that have a minimum inductance greater than

the calculated L1MIN and L2MIN and current rating

greater than IL1P and IL2P, respectively. The recom-

mended saturation current limit of the selected inductor

is 10% higher than the inductor peak current:

For simplifying further calculations, consider L1 and L2

as a single inductor with L1 and L2 connected in parallel.

The combined inductance value and current is calcu-

lated as follows:

MIN MIN

MIN MIN MIN

L1 L2

LL1 L2

and:

AVG AVG

AVG

IL IL1 IL2= +

where ILAVG represents the total average current through

both the inductors together for SEPIC configuration. Use

these values in the calculations for SEPIC configuration

in the following sections.

Select coupling capacitor CS so that the peak-to-

peak ripple on it is less than 2% of the minimum input

supply voltage. This ensures that the second-order

effects created by the series resonant circuit comprising

L1, CS, and L2 does not affect the normal operation of

the converter. Use the following equation to calculate the

minimum value of CS:

LED MAX

SIN_MIN SW

CV 0.02 f

≥

××

where CS is the minimum value of the coupling capacitor

in farads, ILED is the LED current in amperes, and the

factor 0.02 accounts for 2% ripple.

Slope Compensation

The MAX16814 generates a current ramp for slope

compensation. This ramp current is in sync with

the switching frequency and starts from zero at the

beginning of every clock cycle and rises linearly to

reach 50FA at the end of the clock cycle. The slope-

compensating resistor, RSCOMP, is connected between

the CS input and the source of the external MOSFET.

This adds a programmable ramp voltage to the CS input

voltage to provide slope compensation.

Use the following equation to calculate the value of slope

compensation resistance (RSCOMP).

For boost configuration:

( )

LED IN_MIN CS

SCOMP MIN SW

V 2V R 3

RL 50 A f 4

− ××

=× ××F

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For SEPIC and coupled-inductor boost-buck:

( )

LED IN_MIN CS

SCOMP MIN SW

V V R3

RL 50 A f 4

−

××

=× ××F

where VLED and VIN_MIN are in volts, RSCOMP and RCS

are in ohms, LMIN is in henries and fSW is in hertz.

The value of the switch current-sense resistor, RCS, can

be calculated as follows:

For boost:

( )

MAX LED IN_MIN

LP MN SW

D V 2V R 3

0.396 0.9 I R 4L f

× − ××

×=× + ××

For SEPIC and boost-buck:

( )

MAX LED IN_MIN

MN SW

D V V R3

0.396 0.9 I R 4L f

× − ××

×=× + ××

where 0.396 is the minimum value of the peak cur-

rent-sense threshold. The current-sense threshold also

includes the slope compensation component. The mini-

mum current-sense threshold of 0.396 is multiplied by

0.9 to take tolerances into account.

Output Capacitor Selection

For all the three converter topologies, the output capaci-

tor supplies the load current when the main switch is

on. The function of the output capacitor is to reduce the

converter output ripple to acceptable levels. The entire

output-voltage ripple appears across constant current-

sink outputs because the LED string voltages are stable

due to the constant current. For the MAX16814, limit

the peak-to-peak output voltage ripple to 200mV to get

stable output current.

The ESR, ESL, and the bulk capacitance of the output

capacitor contribute to the output ripple. In most of the

applications, using low-ESR ceramic capacitors can

dramatically reduce the output ESR and ESL effects.

To reduce the ESL and ESR effects, connect multiple

ceramic capacitors in parallel to achieve the required

bulk capacitance. To minimize audible noise during

PWM dimming, the amount of ceramic capacitors on the

output are usually minimized. In this case, an additional

electrolytic or tantalum capacitor provides most of the

bulk capacitance.

External MOSFET Selection

The external MOSFET should have a voltage rating

sufficient to withstand the maximum output voltage

together with the rectifier diode drop and any

possible overshoot due to ringing caused by parasitic

inductances and capacitances. The recommended

MOSFET VDS voltage rating is 30% higher than the sum

of the maximum output voltage and the rectifier diode

drop.

The recommended continuous drain current rating of the

MOSFET (ID), when the case temperature is at +70NC, is

greater than that calculated below:

RMS AVG MAX

ID IL D 1.3



= ××





The MOSFET dissipates power due to both switching

losses and conduction losses. Use the following equa-

tion to calculate the conduction losses in the MOSFET:

COND AVG MAX DS(ON)

P IL D R= ××

where RDS(ON) is the on-state drain-to-source resistance

of the MOSFET.

Use the following equation to calculate the switching

losses in the MOSFET:

AVG LED GD SW

SW GON GOFF

IL V C f

P2 II



× ××

= ×+





where IGON and IGOFF are the gate currents of the

MOSFET in amperes, when it is turned on and turned

off, respectively. CGD is the gate-to-drain MOSFET

capacitance in farads.

Rectier Diode Selection

Using a Schottky rectifier diode produces less forward

drop and puts the least burden on the MOSFET during

reverse recovery. A diode with considerable reverse-

recovery time increases the MOSFET switching loss.

Select a Schottky diode with a voltage rating 20% higher

than the maximum boost-converter output voltage and

current rating greater than that calculated in the follow-

ing equation:

−= ×

D AVG MAX

I IL (1 D ) x 1.2

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MAX16814 Integrated, 4-Channel, High-Brightness LED

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Feedback Compensation

During normal operation, the feedback control loop

regulates the minimum OUT_ voltage to 1V when LED

string currents are enabled during PWM dimming. When

LED currents are off during PWM dimming, the control

loop turns off the converter and stores the steady-state

condition in the form of capacitor voltages, mainly the

output filter capacitor voltage and compensation capaci-

tor voltage. For the MAX16814A_ _ and the MAX16814U_

_, when the PWM dimming pulses are less than or equal

to 5 switching clock cycles, the feedback loop regulates

the converter output voltage to 95% of OVP threshold.

The worst-case condition for the feedback loop is when

the LED driver is in normal mode regulating the minimum

OUT_ voltage to 1V. The switching converter small-signal

transfer function has a right-half plane (RHP) zero for

boost configuration if the inductor current is in continuous

conduction mode. The RHP zero adds a 20dB/decade

gain together with a 90N-phase lag, which is difficult to

compensate.

The worst-case RHP zero frequency (fZRHP) is

calculated as follows:

For boost configuration:

LED MAX

ZRHP LED

V (1 D )

f 2 LI

−

=π× ×

For SEPIC and coupled-inductor boost-buck

configurations:

LED MAX

ZRHP LED MAX

V (1 D )

f 2 LI D

−

=π× × ×

where fZRHP is in hertz, VLED is in volts, L is the induc-

tance value of L1 in henries, and ILED is in amperes. A

simple way to avoid this zero is to roll off the loop gain

to 0dB at a frequency less than one fifth of the RHP zero

frequency with a -20dB/decade slope.

The switching converter small-signal transfer function

also has an output pole. The effective output impedance

together with the output filter capacitance determines the

output pole frequency fP1 that is calculated as follows:

For boost configuration:

LED

P1 LED OUT

f2V C

=×π× ×

For SEPIC and coupled-inductor boost-buck configurations:

LED MAX

P1 LED OUT

f2V C

=×π× ×

where fP1 is in hertz, VLED is in volts, ILED is in amperes,

and COUT is in farads.

Compensation components (RCOMP and CCOMP)

perform two functions. CCOMP introduces a low-

frequency pole that presents a -20dB/decade slope

to the loop gain. RCOMP flattens the gain of the error

amplifier for frequencies above the zero formed by

RCOMP and CCOMP. For compensation, this zero is

placed at the output pole frequency fP1 so that it pro-

vides a -20dB/decade slope for frequencies above fP1

to the combined modulator and compensator response.

The value of RCOMP needed to fix the total loop gain

at fP1 so that the total loop gain crosses 0dB with

-20dB/decade slope at 1/5 the RHP zero frequency is

calculated as follows:

For boost configuration:

ZRHP CS LED

COMP P1 COMP LED MAX

f RI

R5 f GM V (1 D )

××

=× × × ×−

For SEPIC and coupled-inductor boost-buck

configurations:

ZRHP CS LED MAX

COMP P1 COMP LED MAX

f RI D

R5 f GM V (1 D )

×××

=× × × ×−

where RCOMP is the compensation resistor in

ohms, fZRHP and fP2 are in hertz, RCS is the switch

current-sense resistor in ohms, and GMCOMP is the

transconductance of the error amplifier (600FS).

The value of CCOMP is calculated as follows:

COMP COMP Z1

C 2R f

=π× ×

where fZ1 is the compensation zero placed at 1/5 of

the crossover frequency that is, in turn, set at 1/5 of the

fZRHP.

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

If the output capacitors do not have low ESR, the ESR

zero frequency may fall within the 0dB crossover fre-

quency. An additional pole may be required to cancel

out this pole placed at the same frequency. This is

usually implemented by connecting a capacitor in paral-

lel with CCOMP and RCOMP. Figure 5 shows the SEPIC

configuration and Figure 6 shows the coupled-inductor

boost-buck configuration.

Analog Dimming Using External

Control Voltage

Connect a resistor RSETI2 to the SETI input as shown

in Figure 7 for controlling the LED string current using

an external control voltage. The MAX16814 applies a

fixed 1.23V bandgap reference voltage at SETI and

measures the current through SETI. This measured current

multiplied by a factor of 1220 is the current through

each one of the four constant current-sink channels.

Adjust the current through SETI to get analog dimming

functionality by connecting the external control voltage

to SETI through the resistor RSETI2. The resulting change

in the LED current with the control voltage is linear and

inversely proportional. The LED current control range

remains between 20mA to 150mA.

Use the following equation to calculate the LED current

set by the control voltage applied:

( )

OUT SETI SETI2

1.23 V

1500

I 1220

−

=+×

Figure 5. SEPIC Configuration

OUT1

OVPCSNDRVIN

DRV

VCC

CSD1

UP TO 40V

RCS

RSCOMP

MAX16814

OUT2

OUT3

OUT4

SETI

FLT

VCC

RSETI

RSDT

PGND LEDGNDSGND

VIN

4.75V TO 40V

NR1

DIM

COMP

RCOMP

CCOMP

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MAX16814 Integrated, 4-Channel, High-Brightness LED

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PCB Layout Considerations

LED driver circuits based on the MAX16814 device use

a high-frequency switching converter to generate the

voltage for LED strings. Take proper care while laying

out the circuit to ensure proper operation. The switching-

converter part of the circuit has nodes with very fast

voltage changes that could lead to undesirable effects

on the sensitive parts of the circuit. Follow the guidelines

below to reduce noise as much as possible:

1) Connect the bypass capacitor on VCC and DRV as

close to the device as possible and connect the

capacitor ground to the analog ground plane using

vias close to the capacitor terminal. Connect SGND

of the device to the analog ground plane using a via

close to SGND. Lay the analog ground plane on the

inner layer, preferably next to the top layer. Use the

analog ground plane to cover the entire area under

critical signal components for the power converter.

2) Have a power ground plane for the switching-

converter power circuit under the power components

(input filter capacitor, output filter capacitor, inductor,

MOSFET, rectifier diode, and current-sense resis-

tor). Connect PGND to the power ground plane as

close to PGND as possible. Connect all other ground

connections to the power ground plane using vias

close to the terminals.

3) There are two loops in the power circuit that carry

high-frequency switching currents. One loop is when

the MOSFET is on (from the input filter capacitor

positive terminal, through the inductor, the internal

MOSFET, and the current-sense resistor, to the input

capacitor negative terminal). The other loop is when

the MOSFET is off (from the input capacitor positive

terminal, through the inductor, the rectifier diode,

output filter capacitor, to the input capacitor negative

terminal). Analyze these two loops and make the loop

areas as small as possible. Wherever possible, have a

return path on the power ground plane for the switch-

ing currents on the top layer copper traces, or through

power components. This reduces the loop area con-

siderably and provides a low-inductance path for

the switching currents. Reducing the loop area also

reduces radiation during switching.

4) Connect the power ground plane for the constant-

current LED driver part of the circuit to LEDGND as

close to the device as possible. Connect SGND to

PGND at the same point.

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MAX16814 Integrated, 4-Channel, High-Brightness LED

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Figure 7. Analog Dimming with External Control Voltage

Figure 6. Coupled-Inductor Boost-Buck Configuration

OUT1

OVPCSNDRVIN

DRV

VCC

(1:1)

UP TO 40V

RCS

RSCOMP

MAX16814

OUT2

OUT3

OUT4

SETI

FLT

VCC

RSETI

RSDT

PGND LEDGNDSGND

VIN

4.75V TO 40V

NR1

DIM

COMP

RCOMP

CCOMP

SETI

1.23V

MAX16814

RSETI2

RSETI VC

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Typical Operating Circuit

OUT1

OVPCSNDRVIN

DRV

VCC

UP TO 40V

RCS

RSCOMP

MAX16814

OUT2

OUT3

OUT4

SETI

FLT

VCC

RSETI

RSDT

PGND LEDGNDSGND

VIN

4.75V TO 40V

NR1

DIM

COMP

RCOMP

CCOMP

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Chip Information

PROCESS: BiCMOS DMOS

Package Information

For the latest package outline information and land patterns, 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.

PACKAGE

TYPE

PACKAGE

CODE

OUTLINE

NO.

LAND PATTERN

NO.

20 TSSOP-EP U20E+1 21-0108 90-0114

20 TQFN-EP T2044+3 21-0139 90-0037

20 QFND-EP

(Side Wettable) G2044Y+1 21-0576 90-0360

+Denotes a lead(Pb)-free/RoHS-compliant package.

*EP = Exposed pad.

/V denotes an automotive qualified part; (SW) = side wettable.

Ordering Information

PART TEMP RANGE PIN-PACKAGE

MAX16814ATP+ -40°C to +125°C20 TQFN-EP*

MAX16814ATP/V+ -40°C to +125°C20 TQFN-EP*

MAX16814AGP/VY+

-40°C to +125°C20 QFND-EP* (SW)

MAX16814AUP+ -40°C to +125°C20 TSSOP-EP*

MAX16814AUP/V+ -40°C to +125°C20 TSSOP-EP*

MAX16814BETP+ -40°C to +85°C20 TQFN-EP*

MAX16814BEUP+ -40°C to +85°C20 TSSOP-EP*

MAX16814BUTP+ 0°C to +85°C20 TQFN-EP*

MAX16814BUUP+ 0°C to +85°C20 TSSOP-EP*

MAX16814UTP+ 0°C to +85°C20 TQFN-EP*

MAX16814UUP+ 0°C to +85°C20 TSSOP-EP*

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MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

Revision History

REVISION

NUMBER

REVISION

DATE DESCRIPTION PAGES CHANGED

0 7/09 Initial release —

1 9/09 Correction to slope compensation description and block diagram 10, 18

2 11/09 Correction to synchronization description frequency and minor

edits 1–4, 8, 12–20, 22, 25

3 2/10 Correction to CSYNC formula 13

4 6/10 Added MAX16814BE _ _ parts; corrected specification 1–4, 8, 13, 25

5 3/11 Correction to output current accuracy specification and Absolute

Maximum Ratings 1, 2, 4

6 10/11 Correction to the last formula and description 19

7 1/13 Added side-wettable package option and updated EN leakage in

Electrical Characteristics 1, 2, 4, 8, 9, 23, 24

8 4/13 Minor corrections to Figures 1, 2, and the LED Diming Control,

Rectifier Diode Selection, and Feedback Compensation sections 10, 11, 14, 18, 19

9 11/13 Corrected VCOMP offset voltage in Figure 1 10

10 2/15 Updated the Benefits and Features section 1

11 3/16 Updated the LED Dimming Control section 14

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.

│

MAX16814 Integrated, 4-Channel, High-Brightness LED

Driver with High-Voltage DC-DC Controller

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.