Linear Technology DC1784A Quick setup guide

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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

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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

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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.

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DEMO MANUAL DC1784A
Demo circuit options
Figure 1. Test Procedure Setup Drawing for DC1784A

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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
0.2
0.4
0.6
0.8
1
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)
80
82
84
86
88
90
92
94
96
98
100
0 5 10 15 20 25 30 35 40 45
EFFICIENCY (%)
PVIN (V)

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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

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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 GND GND
UP TO 50V LED 1A
GND VIN PVIN GND GND GND GND
2.5V - 40V
SD25-470-R
0603 0603 0603
0603
0603 0603 0603 0603
0603 0603 0603
0603
0603 0603 0603
UP TO 50V LED 1A UP TO 50V LED 1A
310kHz
OUT1
LED2+
OUT2
PVIN
OUT2
OUT3
OUT1
VIN
LED3+
LED1+
OUT3
PVIN
PVIN
PVIN
PVIN
PVIN
PVIN
INTVCC
PVINPVIN PVIN
REF
INTVCC
REF
PVIN
PVIN
PVIN
M4 SI7113DN M4 SI7113DN
2
4
7
3
16
8 5
R36 OPT 0603 R36 OPT 0603
C12 6.8nF C12 6.8nF
R38 OPT R38 OPT
C31C31
E8E8
R37 OPT 0603 R37 OPT 0603
R9
23.2K
R9
23.2K
E26E26
R29 0 1206 R29 0 1206
E20E20
R2 0.25 2010 R2 0.25 2010
E2E2 C29C29
E17E17
R43
OPT
0603
R43
OPT
0603
R20
140K
R20
140K
R3 0.25 2010 R3 0.25 2010
C6 4.7uF
100V 1210
C6 4.7uF
100V 1210
C34
OPT
1210
C34
OPT
1210
R8
23.2K
R8
23.2K
L1 10uH L1 10uH
M6
SI7113DN
M6
SI7113DN
2
4
7
3
16
8
5
D1
PDS360
D1
PDS360
12
3
M1
BSC039N06NS
M1
BSC039N06NS
2
4
7
3
1 6
8
5
R26 100K R26 100K
J2J2
C14 0.1uF C14 0.1uF
E19E19
C27C27
C35
OPT
1210
C35
OPT
1210
M2 SI7113DN M2 SI7113DN
2
4
7
3
16
8
5
R23 100K R23 100K
R31 OPT R31 OPT
E24E24
R24 100K R24 100K
R19 1M R19 1M
R25 100K R25 100K
+
C37 33uF 50V
+
C37 33uF 50V
E27E27
R1 47.5K R1 47.5K
R46 OPT R46 OPT
C15 0.1uF C15 0.1uF
R12 0.008 2010 R12 0.008 2010
C7 4.7uF
100V 1210
C7 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
D4
ES1B
D4
ES1B
12
R45 OPT 0603 R45 OPT 0603
R30
0
R30
0
D3
PDS360
D3
PDS360
12
3
E16E16
E9E9
R4 0.25 2010 R4 0.25 2010
C28
1210
OPT C28
1210
OPT
E10E10
C19C19
R5 3.9K R5 3.9K
R21
140K
R21
140K
C32C32
C25C25
R44 OPT 0603 R44 OPT 0603
C3 4.7uF
50V
1210 C3 4.7uF
50V
1210
E14E14
C26 OPT
1210
C26 OPT
1210
C11 6.8nF C11 6.8nF
E28E28
R7
3.9K
R7
3.9K
R42
OPT
0603
R42
OPT
0603
E21E21
R10
23.2K
R10
23.2K
D2
PDS360
D2
PDS360
1
2
3
R15 1M R15 1M
D5
ES1B
D5
ES1B
12
C1 1uF 50V
0805
C1 1uF 50V
0805
C36
OPT
1210
C36
OPT
1210
R40 OPT R40 OPT
C33C33
C18 OPT C18 OPT
C8
0.1uF
C8
0.1uF
R11 0.008 2010 R11 0.008 2010
R17 1M R17 1M
C16 OPT C16 OPT
C24
OPT
C24
OPT
R28
0
R28
0
E7E7
D6
ES1B
D6
ES1B
12
C4 4.7uF 50V 1210 C4 4.7uF 50V 1210
R22
140K
R22
140K
E4E4
L2 10uH L2 10uH
C9
10uF 10V
C9
10uF 10V
C2 4.7uF 50V 1210 C2 4.7uF 50V 1210
R41 OPT
0603
R41 OPT
0603
R27
105K
R27
105K
E29E29
C22
OPT
C22
OPT
E11E11
C20C20
C5 4.7uF
100V 1210
C5 4.7uF
100V 1210
R34 OPT R34 OPT
E12E12
C17
OPT
C17
OPT
E22E22
U1
LT3797EUKG
U1
LT3797EUKG
FLT1
1
FLT2
2
FLT3
3
PWM1 4 PWM2 5 PWM3 6
REF
7
CTRL1
8
CTRL2
9
CTRL3
10
RT
11
SYNC
12
TG1 14
ISN115
ISP116
FBH1 17
VC1
19
SS1
20
SENSEN121
SENSEP122
GATE1 23
GATE2 24
SENSEP225
SENSEN226
SS2
27
VC2
28
FBH2 30
ISP231
ISN232
TG2 33
TG3 35
ISN336
ISP337
FBH3 38
VC3
40
SS3
41
SENSEN342
SENSEP343
GATE3 44
INTVCC
45
INTVCC
46
SW2 47
BOOST 48
SW1 49
VIN
50
EN/UVLO
51
OVLO
52
GND
53
R32 OPT R32 OPT
C23
OPT
C23
OPT
E23E23
L3 10uH L3 10uH
E25E25
E13E13
E18E18
R33 OPT R33 OPT
M3
BSC039N06NS
M3
BSC039N06NS
2
4
7
3
1 6
8
5
L4
47uH
L4
47uH
R6 3.9K R6 3.9K
R35 OPT 0603 R35 OPT 0603
R14 1M R14 1M
C10 6.8nF C10 6.8nF
R18 1M R18 1M
E5E5
C21C21
R16 1M R16 1M
M5
BSC039N06NS
M5
BSC039N06NS
2
4
7
3
1 6
8
5

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DEMO MANUAL DC1784A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●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
Copyright © 2004, Linear Technology Corporation