Linear Technology DC1784A Quick setup guide

dc1784af

DEMO MANUAL DC1784A

Description

LT3797EUKG

Triple LED Boost Controller

DC1784A is a triple boost LED driver featuring the LT3797

triple boost LED controller. It accepts an input voltage

from 2.5V to 40V(with higher transient) and drives three

independent strings of up to 50V LEDs at 1A. DC1784A

features independent PWM and analog dimming of each

of the three LED strings. Each of the three channels has

its own short-circuit protection, open LED protection, and

FAULT flag output.

Each or every channel can be altered to run as a different

topology such as buck-boost mode, buck mode, or SEPIC

depending upon the relationship between input and output

voltage. Although the boost is set up to power 50V of LEDs

at 1A, the maximum LED string voltage can be changed

to almost 100V and the LED current can be adjusted by

merely changing a few resistors and external components.

DC1784A features high efficiency at 310kHz switching

frequency. At high LED string voltages up to 50V and 1A

of LED current, the triple LED boost controller has 93.5%

efficiency. The switching frequency can be adjusted be-

tween 100kHz and 1MHz with a single resistor. All three

channels run in-phase with each other and an external

SYNC pin can be used to set the switching frequency and

phasing, as well as to optimize PWM dimming.

For low input voltage operation, down to 2.5V, the CTRL

pin voltage is reduced as the input voltage drops below

10.5V, reducing LED brightness and restraining the peak

switch currents in order to limit thermal rise on this PCB.

The LT3797 has a unique, internal buck-boost INTVCC

supply that powers the gate drivers at 7.8V, regardless

of the state of the input voltage, rather than using an LDO

from the input. UVLO turns the LEDs off when VIN drops

below 2.5V. Internal OVLO turns off the switching when

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

Technology Corporation. All other trademarks are the property of their respective owners.

the input exceeds 41V, but OVLO can be programmed

externally to a lower voltage if desired. The LT3797 can

withstand transients up to 60V. DC1784A can withstand

transients up to 50V with C3 > 50V rating.

Small ceramic input and output capacitorsare used to save

space and cost. The open LED overvoltage protection uses

the IC’s constant voltage regulation loop to regulate the

output to approximately 55V if the LED string is opened

although it may reach 59V peak during transient from

running LEDs to open. The unique FBH (feedback high)

pins allow the overvoltage protection of non-grounded

LED driver topologies such as buck-boost mode and buck

mode to be accomplished with just two resistors.

Modifications can be made to DC1784A in order to convert

the independent channels to higher or lower power or from

LED drivers to constant voltage regulators. They can easily

be changed from boost topology to SEPIC, buck mode, or

buck-boost mode LED drivers. Please consult the factory

or the LT3797 data sheet for details.

The LT3797 data sheet gives a complete description of

the device, operation and applications information. The

data sheet must be read in conjunction with this demo

manual for DC1784A. The LT3797EUKG is assembled in

a52-lead (7mm ×8mm) plastic QFN UKG package with

a thermally enhanced ground pad. Proper board layout

is essential for maximum thermal performance. See the

data sheet section ‘Layout Considerations’.

Design files for this circuit board are available at

http://www.linear.com/demo/DC1784A

dc1784af

DEMO MANUAL DC1784A

Quick start proceDure

DC1784A is easy to set up to evaluate the performance of

the LT3797EUKG. Follow the procedure below:

1. Connect three strings of LEDs that will run with forward

voltage less than 50V(at 1A), but greater than PVIN,

to the LED+and GND terminals on the PCB as shown

in Figure 1.

2. Connect the EN/UVLO terminal to GND.

3. With power off, connect the input power supply to the

PVIN and GND terminals. Make sure that the PVIN DC

input voltage does not exceed 40V (or VLED).

4. Turn the input power supply on and make sure the

voltage is between 2.5V and 40V (or VLED).

5. Connect the PWM1-3 input terminals to INTVCC or VREF

to enable 100% brightness control when EN/UVLO is

released.

6. Release the EN/UVLO-to-GND connection.

7. Observe the LED strings running at the programmed

LED current.

8. To change the brightness with analog dimming, sim-

ply attach a voltage source on any or all of the CTRL

terminals and set the voltage(s) between 0V and 1.5V.

See data sheet for details.

9. To change brightness with PWM dimming, remove the

connection from PWM1-3 to INTVCC or VREF and attach

a3.3V to 5V rectangular waveform with varying duty

cycle.

performance summary

PARAMETER CONDITIONS VALUE (TYPICAL)

Input Voltage PVIN Range Operating VIN = PVIN 2.5V to VLED (Up to 40V)

Switching Frequency R1 = 47.5k 310kHz

ILED CH1, CH2, CH3 R2, R3, R4 = 0.25Ω 10.5V < PVIN < VLED (40V) 1.0A

Low PVIN ILED (CTRL foldback) R2, R3, R4 = 0.25Ω PVIN = 4.0V

R2, R3, R4 = 0.25Ω PVIN = 6.0V

R2, R3, R4 = 0.25Ω PVIN = 9.0V

280mA

525mA

890mA

VLED Range CH1, CH2, CH3 R8, R9, R10 = 23.2k R14, R15, R16 = 1M PVIN < VLED < 50V

Open LED Voltage CH1, CH2, CH3 R8, R9, R10 = 23.2k R14, R15, R16 = 1M 55V

Typical Efficiency (100% PWM Duty Cycle) PVIN = 14V VLED = 50V and ILED = 1A CH1, CH2, CH3 93.5%

PVIN Under Voltage Lockout (Falling Turn-Off) R26 = 100k and R27 = 105k 2.5V

PVIN Under Voltage Lockout (Rising Turn-On) R26 = 100k and R27 = 105k 2.6V

INTVCC Operating 7.5V

Peak Switch Current Limit CH1, CH2, CH3 R11, R12, R13 = 0.008Ω 12.5A

dc1784af

DEMO MANUAL DC1784A

Demo circuit options

DC1784A can be adjusted for higher output voltage, dif-

ferent LED current, or different topology. The following

options are for simple changes to the demonstration

circuit. The data sheet gives more information regarding

designing with the LT3797. For more information, see

the data sheet for details or contact Linear Technology

technical support.

Maximum LED Voltage

DC1784A is set for 55V of overvoltage protection and the

maximum LED string voltage used on the standard build

should be 50V. However, the output can go up to 100V,

so OVP can be set at about 93V for maximum LED voltage

and the maximum LED string voltage is therefore about

87V. The limits are based upon open LED overshoot and

voltage and current regulation regions. If changes are

made in the FB resistors for higher voltage, the MOSFET

and catch diode should be switched out for higher voltage

devices. See the LT3797 data sheet for details.

Current or Voltage Regulation

The LT3797 can be used for constant current or voltage

regulation. If the load placed on the LED+to GND terminals

allows VOUT to climb high enough for VISP-FBH = 1.2V, then

the voltage regulation loop of the converter takes over. In

this case, the compensation for a given channel should be

adjusted for proper use as a constant voltage regulator.

The IC can be used as a boost or SEPIC constant voltage

regulator. Output voltage can be almost as high as 100V

when used as a constant voltage regulator.

LED Current and Switch Current

LED current on DC1784A is set for 1A with 0.25Ω resis-

tors R2, R3, R4. For a different maximum LED current,

change this resistor:

250mV/RLED = ILED.

A change in LED current or input voltage may lead to higher

or lower maximum switch current. R11, R12, R13 can be

changed to alter the maximum switch current for different

applications. 100mV/RSENSE = peak switch current.

Overvoltage Protection

Overvoltage protection is set with resistor pairs R8 & R14,

R9 & R15, R10 & R16. The high side feedback method

allows simple changes for different topologies.

For buck mode and buck-boost mode, see the data sheet

for details how to set the feedback resistors. Note that

R35, R36, R37 are provided as optional placeholders on

the demo circuit for simple feedback resistor changes for

these topologies.

BOOST, BUCK MODE, BUCK-BOOST MODE, SEPIC

Any channel of the DC1784A can be changed to a differ-

ent topology than boost. A few simple changes including

feedback overvoltage protection feedback resistors, out-

put resistor, components, and connection to input can

be made. Please consult the LT3797 data sheet and the

factory for details.

Undervoltage and Overvoltage Lockout

UVLO can be adjusted by changing the values of R26

and R27.

The LT3797 has an internal 41V OVLO that protects the IC

from switching at high input voltage transients. However,

an additional OVLO pin can be used to set a lower OVLO

using resistors R28, R31, and/or R46.

dc1784af

DEMO MANUAL DC1784A

Demo circuit options

Figure 1. Test Procedure Setup Drawing for DC1784A

dc1784af

DEMO MANUAL DC1784A

Figure 2. DC1784A 12VIN 100Hz PWM Dimming Waveforms at Different PWM Duty Cycles with 250:1 in Bold.

ILED Waveform (500mA/Div) Is on Top (with 50V LED String) and IL1 Waveform (2A/Div) Is on the Bottom

Figure 3. DC1784A CTRL LED Current Foldback at Low PVIN with UVLO Falling and Rising

Figure 4. DC1784A Efficiency at Maximum ILED vs PVIN with 50V LEDs (at 1A) on All Three Channels

Demo circuit options

250:1

ILED

IL1

0.2

0.4

0.6

0.8

0 2 4 6 8 10 12 14

ILED (A)

PVIN (V)

TURN-ON

(RISING)

30 32 34 36 38 40 42

OVLO

(RISING)

TURN-ON

(FALLING)

UVLO

(FALLING)

100

0 5 10 15 20 25 30 35 40 45

EFFICIENCY (%)

PVIN (V)

dc1784af

DEMO MANUAL DC1784A

parts List

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 1 C1 Cap., X7R, 1µF, 50V, 10%, 0805 MURATA, GRM21BR71H105KA12L

2 6 C2, C3, C4, C31, C32, C33 Cap., X7R, 4.7µF, 50V, 10%, 1210 MURATA, GRM32ER71H475KA88L

3 9 C5, C6, C7, C19, C20, C21, C25,

C27, C29

Cap., X7S, 4.7µF, 100V, 20%, 1210 TDK C3225X7S2A475M

4 4 C8, C13, C14, C15 Cap., X7R, 0.1µF, 10V, 10%, 0603 AVX, 0603ZC104KAT2A

5 1 C9 Cap., X5R, 10µF, 10V, 20%, 0603 SAMSUNG CL10A106MP8NNNC

6 3 C10, C11, C12 Cap., X7R, 6800pF, 25V, 10%, 0402 AVX, 04023C682KAT2A

7 3 D1, D2, D3 DIODE, PDS360, POWERDI-5 DIODES/ZETEX, PDS360-13

8 3 L1, L2, L3 IND, 10µH, HC9-100-R COILTRONICS, HC9-100-R

9 1 L4 IND., 47µH, SD SERIES, IND-SD25 COILTRONICS, SD25-470-R

10 3 M1, M3, M5 Mosfet, N-Channel, BSC039N06NS, PWRPAK SO-8 INFINEON, BSC039N06NS

11 3 M2, M4, M6 Mosfet, P-Channel, SI7113DN, PWRPAK1212-8 VISHAY, SI7113DN-T1-GE3

12 1 R1 RES., CHIP, 47.5k, 1/16W, 1%, 0402 VISHAY, CRCW040247K5FKED

13 3 R2, R3, R4 RES., CHIP, 0.25Ω, 1W, 1%, 2010 IRC, LRC-LR2010LF-01-R250-F

14 3 R5, R6, R7 RES., CHIP, 3.9k, 1%, 0402 VISHAY, CRCW04023K90FKED

15 3 R8, R9, R10 RES., CHIP, 23.2k, 1/16W, 1%, 0402 VISHAY, CRCW040223K2FKED

16 3 R11, R12, R13 RES., CHIP, 0.008Ω, 1W, 1%, 2010 SEI, CSRF2010FT8L00

17 3 R14, R15, R16 RES., CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA

18 1 U1 IC, LT3797EUKG QFN(52)(UKG)-7mm ×8mm LINEAR TECH.CORP. LT3797EUKG#PBF

Optional Electrical Components

1 0 C16, C17, C18, C22, C23, C24 CAP., OPT 0402 OPT

2 0 C26, C28, C30, C34, C35, C36 CAP., OPT 1210 OPT

3 1 C37 Cap., ALUM, 33µF, 50V, 6.3 ×7.7 PANASONIC, EEHZA1H330XP

4 3 D4, D5, D6 DIODE, ES1B, 150V/1A, SMA DIODES/ZETEX, ES1B-13-F

5 3 R17, R18, R19 RES., CHIP, 1M, 1/16W, 1%, 0402 VISHAY, CRCW04021M00FKED

6 3 R20, R21, R22 RES., CHIP, 140k, 1/16W, 1%, 0402 VISHAY, CRCW0402140KFKED

7 3 R23, R24, R25 RES., CHIP, 100k, 1/10W, 1%, 0603 VISHAY, CRCW0603100KFKEA

8 1 R26 RES., CHIP, 100k, 1/16W, 1% , 0402 VISHAY, CRCW0402100KFKED

9 1 R27 RES., CHIP, 105k, 1/16W, 1% , 0402 VISHAY, CRCW0402105KFKED

10 1 R28 RES., CHIP, 0Ω, 0402 VISHAY, CRCW04020000Z0ED

11 1 R29 RES., CHIP, 0Ω, 1/4W, 1% , 1206 VISHAY, CRCW12060000Z0EA

12 1 R30 RES., CHIP, 0Ω, 1/10W, 1%, 0603 VISHAY, CRCW06030000Z0EA

13 0 R31 to R34, R46 RES., OPT, 0402 OPT

14 0 R35 to R45 RES., OPT, 0603 OPT

Hardware

1 7 E2, E10, E11, E12, E16, E17, E18 TESTPOINT, TURRET 0.094" MILLMAX, 2501-2-00-80-00-00-07-0

2 20 E4 to E9, E13 to E15, E19 to E29 TESTPOINT, TURRET 0.064" MILL-MAX, 2308-2-00-80-00-00-07-0

32 J1, J2 CONNECTOR, BANANA JACK KEYSTONE, 575-4

dc1784af

DEMO MANUAL DC1784A

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

schematic Diagram

EN/UVLO

LED1+

LED2+

LED3+

OVLO

CTRL1

CTRL2

CTRL3

INTVCC

FLT1

FLT2

FLT3

SYNC

OUT1

OUT2

OUT3

PWM1

PWM2

PWM3

GND

UP TO 50V LED 1A

GND

VIN

PVIN

GND

2.5V - 40V

SD25-470-R

0603 0603 0603

0603

0603 0603 0603 0603

0603 0603 0603

0603

UP TO 50V LED 1A

310kHz

OUT1

LED2+

OUT2

PVIN

OUT2

OUT3

OUT1

VIN

LED3+

LED1+

OUT3

PVIN

INTVCC

PVINPVIN PVIN

REF

INTVCC

REF

PVIN

SI7113DN

R36

OPT

0603

R36

OPT

0603

C12

6.8nF

C12

6.8nF

R38

OPT

R38

OPT

C31C31

E8E8

R37

OPT

0603

R37

OPT

0603

23.2K

E26E26

R29

1206

R29

1206

E20E20

0.25

2010

0.25

2010

E2E2 C29C29

E17E17

R43

OPT

0603

R43

OPT

0603

R20

140K

R20

140K

0.25

2010

0.25

2010

4.7uF

100V

1210

4.7uF

100V

1210

C34

OPT

1210

C34

OPT

1210

23.2K

10uH

SI7113DN

PDS360

BSC039N06NS

1 6

R26

100K

R26

100K

J2J2

C14

0.1uF

C14

0.1uF

E19E19

C27C27

C35

OPT

1210

C35

OPT

1210

SI7113DN

R23

100K

R23

100K

R31

OPT

R31

OPT

E24E24

R24

100K

R24

100K

R19

R25

100K

R25

100K

C37

33uF

50V

C37

33uF

50V

E27E27

47.5K

R46

OPT

R46

OPT

C15

0.1uF

C15

0.1uF

R12

0.008

2010

R12

0.008

2010

4.7uF

100V

1210

4.7uF

100V

1210

R13

0.008

2010

R13

0.008

2010

J1J1

E6E6

R39

OPT

R39

OPT

C13

0.1uF

C13

0.1uF

C30

OPT

1210

C30

OPT

1210

E15E15

ES1B

R45

OPT

0603

R45

OPT

0603

R30

PDS360

E16E16

E9E9

0.25

2010

0.25

2010

C28

1210

OPT

C28

1210

OPT

E10E10

C19C19

3.9K

R21

140K

R21

140K

C32C32

C25C25

R44

OPT

0603

R44

OPT

0603

4.7uF

50V

1210

4.7uF

50V

1210

E14E14

C26

OPT

1210

C26

OPT

1210

C11

6.8nF

C11

6.8nF

E28E28

3.9K

R42

OPT

0603

R42

OPT

0603

E21E21

R10

23.2K

R10

23.2K

PDS360

R15

ES1B

1uF

50V

0805

1uF

50V

0805

C36

OPT

1210

C36

OPT

1210

R40

OPT

R40

OPT

C33C33

C18

OPT

C18

OPT

0.1uF

R11

0.008

2010

R11

0.008

2010

R17

C16

OPT

C16

OPT

C24

OPT

C24

OPT

R28

E7E7

ES1B

4.7uF

50V

1210

4.7uF

50V

1210

R22

140K

R22

140K

E4E4

10uH

10uF

10V

10uF

10V

4.7uF

50V

1210

4.7uF

50V

1210

R41

OPT

0603

R41

OPT

0603

R27

105K

R27

105K

E29E29

C22

OPT

C22

OPT

E11E11

C20C20

4.7uF

100V

1210

4.7uF

100V

1210

R34

OPT

R34

OPT

E12E12

C17

OPT

C17

OPT

E22E22

LT3797EUKG

FLT1

FLT2

FLT3

PWM1 4

PWM2 5

PWM3 6

REF

CTRL1

CTRL2

CTRL3

SYNC

TG1 14

ISN115

ISP116

FBH1 17

VC1

SS1

SENSEN121

SENSEP122

GATE1 23

GATE2 24

SENSEP225

SENSEN226

SS2

VC2

FBH2 30

ISP231

ISN232

TG2 33

TG3 35

ISN336

ISP337

FBH3 38

VC3

SS3

SENSEN342

SENSEP343

GATE3 44

INTVCC

SW2 47

BOOST 48

SW1 49

VIN

EN/UVLO

OVLO

GND

R32

OPT

R32

OPT

C23

OPT

C23

OPT

E23E23

10uH

E25E25

E13E13

E18E18

R33

OPT

R33

OPT

BSC039N06NS

1 6

47uH

3.9K

R35

OPT

0603

R35

OPT

0603

R14

C10

6.8nF

C10

6.8nF

R18

E5E5

C21C21

R16

BSC039N06NS

1 6

dc1784af

DEMO MANUAL DC1784A

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ●FAX: (408) 434-0507 ●www.linear.com

 LINEAR TECHNOLOGY CORPORATION 2014

LT 0114 • PRINTED IN USA

DEMONSTRATION BOARD IMPORTANT NOTICE

Linear Technology Corporation (LT C ) provides the enclosed product(s) under the following AS IS conditions:

This demonstration board (DEMO BOARD) kit being sold or provided by Linear Technology is intended for use for ENGINEERING DEVELOPMENT

OR EVALUATION PURPOSES ONLY and is not provided by LT C for commercial use. As such, the DEMO BOARD herein may not be complete

in terms of required design-, marketing-, and/or manufacturing-related protective considerations, including but not limited to product safety

measures typically found in finished commercial goods. As a prototype, this product does not fall within the scope of the European Union

directive on electromagnetic compatibility and therefore may or may not meet the technical requirements of the directive, or other regulations.

If this evaluation kit does not meet the specifications recited in the DEMO BOARD manual the kit may be returned within 30 days from the date

of delivery for a full refund. THE FOREGOING WARRANTY IS THE EXCLUSIVE WARRANTY MADE BY THE SELLER TO BUYER AND IS IN LIEU

OF ALL OTHER WARRANTIES, EXPRESSED, IMPLIED, OR STATUTORY, INCLUDING ANY WARRANTY OF MERCHANTABILITY OR FITNESS

FOR ANY PARTICULAR PURPOSE. EXCEPT TO THE EXTENT OF THIS INDEMNITY, NEITHER PARTY SHALL BE LIABLE TO THE OTHER FOR

ANY INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL DAMAGES.

The user assumes all responsibility and liability for proper and safe handling of the goods. Further, the user releases LT C from all claims

arising from the handling or use of the goods. Due to the open construction of the product, it is the user’s responsibility to take any and all

appropriate precautions with regard to electrostatic discharge. Also be aware that the products herein may not be regulatory compliant or

agency certified (FCC, UL, CE, etc.).

No License is granted under any patent right or other intellectual property whatsoever. LT C assumes no liability for applications assistance,

customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.

LT C currently services a variety of customers for products around the world, and therefore this transaction is not exclusive.

Please read the DEMO BOARD manual prior to handling the product. Persons handling this product must have electronics training and

observe good laboratory practice standards. Common sense is encouraged.

This notice contains important safety information about temperatures and voltages. For further safety concerns, please contact a LT C applica-

tion engineer.

Mailing Address:

Linear Technology

1630 McCarthy Blvd.

Milpitas, CA 95035

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