DC1784A - Demo Manual

DEMO MANUAL DC1784A
LT3797EUKG
Triple LED Boost Controller
Description
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 between 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
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 capacitors are 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
a 52-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
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.
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1
DEMO MANUAL DC1784A
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
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).
2
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, simply 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
a 3.3V to 5V rectangular waveform with varying duty
cycle.
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DEMO MANUAL DC1784A
DEmo circuit Options
DC1784A can be adjusted for higher output voltage, different 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
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 different topology than boost. A few simple changes including
feedback overvoltage protection feedback resistors, output 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.
LED current on DC1784A is set for 1A with 0.25Ω resistors R2, R3, R4. For a different maximum LED current,
change this resistor:
250mV/RLED = ILED.
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3
DEMO MANUAL DC1784A
DEmo circuit Options
Figure 1. Test Procedure Setup Drawing for DC1784A
4
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DEMO MANUAL DC1784A
DEmo circuit Options
ILED
250:1
IL1
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
1
OVLO
(RISING)
TURN-ON
(FALLING)
0.6
0.4
0.2
0
0
TURN-ON
(RISING)
4
UVLO
(FALLING)
2
6
PVIN (V)
8
10
12
14 30
32
34
36
38
40
42
Figure 3. DC1784A CTRL LED Current Foldback at Low PVIN with UVLO Falling and Rising
100
98
96
94
92
EFFICIENCY (%)
ILED (A)
0.8
90
88
86
84
82
80
0
5
10
15
20
25
30
35
40
45
PVIN (V)
Figure 4. DC1784A Efficiency at Maximum ILED vs PVIN with 50V LEDs (at 1A) on All Three Channels
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5
DEMO MANUAL DC1784A
Parts List
ITEM
QTY
REFERENCE
PART DESCRIPTION
MANUFACTURER/PART NUMBER
Cap., X7R, 1µF, 50V, 10%, 0805
MURATA, GRM21BR71H105KA12L
Required Circuit Components
1
1
C1
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
3
2
J1, J2
CONNECTOR, BANANA JACK
KEYSTONE, 575-4
6
dc1784af
J2
E2
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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
GND
GND
GND
GND
INTVCC
FLT3
FLT2
FLT1
CTRL3
CTRL2
CTRL1
OVLO
E29
E28
E27
E26
E9
E8
E7
E6
E5
E4
E25
E24
E23
EN/UVLO
GND
VIN
R23
100K
0603
INTVCC
R29
0
1206
INTVCC
VIN
2.5V - 40V
R24
100K
0603
R22
140K
REF
R18
1M
R25
100K
0603
R19
1M
PVIN
R21
140K
R17
1M
PVIN
R32
OPT
R31
OPT
R26
100K
PVIN
PVIN
R27
105K
R28
0
PVIN
R20
140K
R46
OPT
C37
33uF
50V
C1
1uF
50V
0805
+
R33
OPT
C22
OPT
FLT3
FLT2
FLT1
REF
CTRL3
CTRL2
CTRL1
OVLO
100V
1210
1210
C25
C19
C5
4.7uF
R2
0.25 M2
2010 SI7113DN
3
8
2
7
1
6
5
EN/UVLO
VIN
C9
10uF
10V
0603
3
2
1
7
10
9
8
52
51
50
R11
0.008
2010
BSC039N06NS
M1
1210
L1
10uH
D1
2
1
3
PDS360
R34
OPT
R41
OPT
0603
4
C31
C2
4.7uF
50V
1210
5
6
7
8
1
2
3
PVIN
C16
OPT
15
PVIN
45
16
C34
OPT
23
GATE1
4
21
SENSEP1
INTVCC
22
SENSEN1
INTVCC
46
R5
3.9K
C10
6.8nF
4
C32
C3
4.7uF
50V
1210
C17
OPT
310kHz
R1
47.5K
1
PDS360
D2
1210
C35
OPT
OPT
R42
OPT
0603 C23
R7
3.9K
C12
6.8nF
100V
1210
1210
C27
C20
C6
4.7uF
OUT2
C28
OPT
R44
OPT
0603
C18
OPT
0603
C13
0.1uF
OPT
C24
0603
C14
0.1uF
4
0603
C15
0.1uF
D3
1
1210
C36
OPT
R13
0.008
2010
PDS360
BSC039N06NS
M5
2
3
L3
10uH
PVIN
C33
C4
4.7uF
50V
1210
LED2+
R43
OPT
0603
R3
0.25 M4
2010 SI7113DN
8
3
2
7
6
1
5
U1
LT3797EUKG
C11
6.8nF
R6
3.9K
R12
0.008
2010
BSC039N06NS
M3
2
3
L2
10uH
PVIN
TG1
19
VC1
14
ISN1
5
6
7
8
1
2
3
24
28
GATE2
25
SENSEP2
PVIN
VC3
40
ISP1
RT
11
LED1+
GND
53
4
OUT1
C26
OPT
SS1
20
VC2
26
SENSEN2
31
ISP2
32
ISN2
33
TG2
27
PVIN
SS2
44
GATE3
42
SENSEN3
43
SENSEP3
SS3
41
5
6
7
8
1
2
3
36
ISP3
37
SYNC
12
PWM3
PWM2
PWM1
SW2
BOOST
SW1
FBH3
FBH2
FBH1
TG3
35
ISN3
6
5
4
47
48
49
38
30
17
SD25-470-R
L4
47uH
C8
0.1uF 0603
R45
OPT
0603
R37
OPT
0603
PVIN
R36
OPT
0603
PVIN
R35
OPT
0603
R4
0.25 M6
2010 SI7113DN
3
8
2
7
6
1
5
LED3+
PVIN
100V
1210
1210
C29
C21
C7
4.7uF
C30
OPT
OUT3
4
J1
R38
OPT
0603
R16
1M
0603
R15
1M
0603
R14
1M
0603
R39
OPT
0603
D6
ES1B
D5
ES1B
D4
ES1B
R30
0
0603
R40
OPT
0603
REF
23.2K
R10
23.2K
R9
23.2K
R8
1
1
1
2
2
2
OUT3
OUT2
OUT1
E22
E21
E20
E19
E18
E17
E16
E15
E14
E13
SYNC
PWM3
PWM2
PWM1
GND
GND
GND
OUT3
OUT2
OUT1
UP TO 50V LED 1A
E12
LED3+
UP TO 50V LED 1A
E11
LED2+
UP TO 50V LED 1A
E10
LED1+
DEMO MANUAL DC1784A
Schematic Diagram
dc1784af
7
DEMO MANUAL DC1784A
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) 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 LTC 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 LTC 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. LTC assumes no liability for applications assistance,
customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.
LTC 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 LTC application engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation
8
dc1784af
Linear Technology Corporation
LT 0114 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2014
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