Linear Technology DC1470A Quick setup guide

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dc1470af
DEMO MANUAL DC1470A
DESCRIPTION
LT3743 High Current
Synchronous Step-Down LED
Driver with Three-State Control
Demonstrationcircuit1470Aisahighcurrentsynchronous
step-down LED driver with three-state control featuring
the LT
®
3743EUFD. The demo board is optimized for 20A
output from a 12V input. Being an LED driver, the output
current is being regulated until the output voltage reaches
a programmed voltage limit. This voltage limit on this
demo board is set to around 6V by R5 and R6. The 6V is
chosen because of the 6.3V voltage rating of the output
capacitors. The ideal load to be used with this demo board
is a single LED, such as PT120 from Luminus Devices.
Smaller LEDs may not be able to handle the high current,
even for a short period of time. At 20A, the demo circuit can
operate continuously. However, it is necessary to mount
the LED load on a proper heat sink and possibly with a
fan to avoid exceeding its maximum temperate rating.
Note: The DC470A will drive a LED with its cathode
grounded.GroundingcathodeoftheLED allows customers
to use positive input supply.
The input voltage range of the LT3743 itself is 6Vto 36V.
However,the demo board utilizes 30VMOSFETsto demon-
strate best efficiency so the maximum recommended input
voltage is 24V for the demo board. When input is above
20V during PWM dimming, a slightly larger inductance 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.
PERFORMANCE SUMMARY
may be needed. The typical efficiency of the demo board
is 94% from a 12V input to 5V, 20A load. The lower the
input voltage, the higher the efficiency tends to be with
a given load. At output power level of 100W, a couple of
percent of efficiency improvement is a huge advantage in
minimizing temperature rise. If an efficiency measurement
is needed in an application, the output voltage must be
measured at the output capacitors instead of at the LED
load. This prevents cable loss from being counted as a
loss of the board. If efficiency measurement is required
during PWM dimming, the average current and voltage
values should be measured with proper equipment. All
LT3743 circuits turn off unnecessary circuits during PWM
off period to minimize power losses. As a result, efficiency
in many PWM dimming applications is almost the same
as efficiency of the constant current applications.
The DC1470A uses a split output capacitor configuration
to achieve <2μs current rise time from 0A to 20A. To see
the real rise time, connecting wires between the LED and
the board should be minimized to no more than 2 inches
Specifications are at TA= 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
PVIN* Input Supply Range, PVIN = VIN L1 is Optimized for 12V 12 26.4 V
VOUT* Output Voltage With One PT120 LED, 6V is the Over
Voltage Limit
4.5 6 V
IOUT Output Current CTRL_SEL > 1V 18.8 20 21.2 A
fSW Switching Frequency 400 430 460 kHz
IRISE Current Rise Time Following a PWM Rising Edge 2 μs
EFF Efficiency at DC VIN = 12V, VOUT = 5V, IOUT = 20A 94 %
*PVIN and VIN of the demo circuit are limited to 24V typical by the selection of MOSFETs. The LT3743 input range is 6V to 36V. VOUT maximum of the
demo circuit is limited to 6V due to the selection of the output capacitors.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1470A

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DEMO MANUAL DC1470A
total to minimize the wire inductance. 1-inch is even better.
The cathode of the LED should return to LED– with R25
populated with a resistor in a few mΩ. It is recommended
to measure the voltage on R25 with a short 50Ω coax
cable directly into a BNC connector on the oscilloscope.
The current can then be calculated from the measured
voltage. To get accurate current, R25 should be measured
before it is mounted on the board. A current probe adds
more delays to the rise time so using a current probe is
not recommended. If fast rise time measurement is not
necessary, the cathode of the LED can be connected to
GND as shown in Figure 1.
R27 can be used to slow down the gate drive. Slower gate
drive helps to reduce ringing on the SW node without
noticeable effect on the efficiency. A 10Ω is usually more
than enough to completely damp any ringing.
DESCRIPTION
Demonstration circuit 1470A is easy to set up to evalu-
ate the performance of the LT3743. Refer to Figure 1 for
proper measurement equipment setup and follow the
procedure below:
1. With power off, connect the input power supply to PVIN
and GND. The input power supply should have a current
limit of 10A or more.
2. With power off, connect a LED between VOUT and GND
or between VOUT and LED–, if fast rise time is to be
verified. When returning LED to LED–, R25 needs to
be populated. To check voltage across R25, the best
set up is to solder a short 50Ω coax cable across R25.
Connect the other end of the cable directly into a BNC
connector on an oscilloscope. A less perfect but easier
set up is to touch the probe tip directly across the IS+
and IS– terminals with out the probe ground wire. See
Figure 2 for setup. The latter set up tends to have more
noise but is ok for non-critical measurements. The LED
connecting wires should be as short as possible, 1 inch
total being ideal.
3. Turn on the power at the input.
R15, R16 and C15 help filtering out voltage spikes seen
on the SENSE+or SENSE–pin. It is critical to have those
components on a board.
The LT3743 has a three-state control. It can change output
current among zero, a low level and a high level, all in a
few μs. The low current level of the demo board is set to
around 5A. The high current level is 20A. Both levels can
be adjusted by changing the voltage dividers on CTRL_H
and CTRL_L. Applying a PWM signal to CTRL_SEL will
toggletheoutputbetween 5Ato 20A. While applying a PWM
signal to the PWM pin will toggle the output between either
0A to 5A or 0A to 20A depending on the CTRL_SEL level.
The LT3743 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this demo manual
for DC1470A.
QUICK START PROCEDURE
4. At this time, the output current will be slightly below
5A. If no output current is observed, turn off PVIN and
check the connections.
5. To increase the load current to 20A, turn off PVIN. Pull
CTRL_SEL high either by populating R21 or by using an
external voltage source. Make sure the load can handle
20A continuously and the load voltage is not too high
for the board. Then turn on PVIN.
6. Both the low current level, 5A and the high current
level 20A can be adjusted by changing the voltage on
CTRL_L and CTRL_H terminals between 0V and 2V.
7. To evaluate the transient between 0A and a non-zero
current level, apply a PWM signal to the PWM terminal.
The nonzero current level is dictated by the CTRL_SEL
and CTRL_H or CTRL_L voltages.
8. To evaluate the transient between two non-zero cur rent
levels, apply a PWM signal to the CTRL_SEL terminal.
9. To modify the demo board for other applications, please
contact Linear Applications Group for help.

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DEMO MANUAL DC1470A
QUICK START PROCEDURE
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Voltage Across R25
IS– IS+

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DEMO MANUAL DC1470A
PARTS LIST
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 4 C1, C12, C16, C17 CAP., X7R, 4.7μF, 50V, 10%, 1210 MURATA, GRM32ER71H475KA88L
2 1 C2 CAP., X7R, 1μF, 50V, 10%,0805 MURATA, GRM21BR71H105KA12L
3 1 C3 CAP., X7R, 0.22μF, 10V,10%,0603 MURATA, GRM188R71A224KA01D
4 1 C4 CAP., X5R, 22μF, 6.3V, 20%, 0805 MURATA, GRM21BR60J226ME39L
5 6 C5, C6, C18, C21, C23, C25 CAP., POSCAP, 470μF, 6.3V, D4D PANSONIC, 6TPF470MAH
6 1 C7 CAP., C0G, 2nF, 50V, 0603 MURATA, GRM1885C1H202JA01
7 1 C8 CAP., X7R, 1μF, 16V, 10%,0603 MURATA, GRM188R71C105KA12D
8 2 C9,C10 CAP., C0G, 5600pF, 50V, 5% 0603 MURATA, GRM1885C1H562JA01D
9 1 C11 CAP., ALUM., ELECT., 100μF, 50V SUN ELECTRONICS., 50CE100LX
10 1 C15 CAP., X5R, 0.033μF, 50V, 0603 AVX, 06035D333KAT2A
11 1 C26 CAP., X7R, 1200pF, 50V,5%, 0603 AVX, 06035C122JAT2A
12 1 C27 CAP., X7R, 10μF, 25V,10%,1206 MURATA, GRM31CR71E106KA12L
13 1 D1 SCHOTTKY RECTIFIER, 40V, SOD523 NXP SEMI., PMEG4002EB,115
14 1 D2 2.0A LOW VF SCHOTTKY RECTIFIER DIODES INC., DFLS240L-7
15 1 L1 INDUCTOR, 1.3μH WURTH ELECTRONICS, 7443551130
16 2 Q1,Q2 N-CHANNEL MOSFET, LFPAK INFINEON, BSC080N03LS G
17 1 Q3 N-CHANNEL MOSFET, LFPAK INFINEON, BSC011N03LSI
18 2 Q5,Q6 MOSFET, 40V, DUAL N-CHANEL, PPAK VISHAY, Si7234DP
19 1 R1 RES., CHIP, 124k, 1%, 1/W, 0603 VISHAY, CRCW0603124KFKEA
20 1 R2 RES., CHIP, 374k, 1%, 1/W, 0603 VISHAY, CRCW0603374KFKEA
21 1 R3 RES., CHIP, 0.0025Ω, 1W, 1%, 2512 VISHAY, WSL25122L500FEA
22 7 R4, R9, R10, R12, R13, R14, R20 RES., CHIP, 100k, 1%, 1/W, 0603 VISHAY, CRCW0603100KFKEA
23 3 R5, R7, R8 RES., CHIP, 51k, 1%, 1/W, 0603 VISHAY, CRCW060351K0FKEA
24 1 R6 RES., CHIP, 10k, 1%, 1/W, 0603 VISHAY, CRCW060310K0FKEA
25 2 R15, R16 RES., CHIP, 10Ω, 1%, 1/W, 0603 VISHAY, CRCW060310R0FKEA
26 1 R18 RES., CHIP, 24.9k, 1%, 1/W, 0603 VISHAY, CRCW060324K9FKEA
27 1 R19 RES., CHIP, 432k, 1%, 1/W, 0603 VISHAY, CRCW0603432KFKEA
28 1 R23 RES., CHIP, 3.01k, 1%, 1/W, 0603 VISHAY, CRCW06033K01FKEA
29 1 R24 RES., CHIP, 2k, 1%, 1/W, 0603 VISHAY, CRCW06032K00FKEA
30 1 U1 I.C. LT3743EUFD, 28-PIN QFN-4×5 LINEAR TECH., LT3743EUFD#PBF
Additional Demo Board Circuit Components
1 0 C13, C14, C19, C20, C22, C24 CAP., D4D, OPT
2 0 R11, R21, R22, R26 RES., OPT, 0603 VISHAY, CRCW06030000Z0EA
3 2 R17, R27 RES., CHIP, 0Ω, 0603
4 0 R25 RES., CHIP, 2512, OPT
5 0 Q4 OPT
Hardware for Demo Board Only
1 10 E1-E8, E13, E14 TURRET, TESTPOINT, 091" MILL MAX 2501-2-00-80-00-00-07-0
2 4 E9-E12 JACK BANANA KEYSTONE, 575-4
3 4 STAND-OFF STAND-OFF, NYLON 0.5" TALL KEYSTONE, 8833(SNAP ON)

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DEMO MANUAL DC1470A
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
5
5
4
4
3
3
2
2
1
1
D D C C B B A A
6V - 36V
(400kHz)
HIGH CURRENT SYNCHRONOUS
* See Quick Start Guide
*
*
*
VIN
VCC_INT
VIN
VCC_INT
REVISION HISTORY DESCRIPTION DATEAPPROVEDECO REV
WALKER B.PRODUCTION13 10-02-09
REVISION HISTORY DESCRIPTION DATEAPPROVEDECO REV
WALKER B.PRODUCTION13 10-02-09
REVISION HISTORY DESCRIPTION DATEAPPROVEDECO REV
WALKER B.PRODUCTION13 10-02-09
SIZE DATE:
IC NO.
REV
SHEET OF
TITLE:
CONTRACT NO.
APPROVALS
PCB DES.
ENG.
TECHNOLOGY Fax: [phone]
Milpitas, CA 95035 Phone: [phone] McCarthy Blvd. LTC Confidential-For Customer Use Only
CUSTOMER NOTICE
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL APPLICATION. COMPONENT SUBSTITUTION AND PRINTED CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY. CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
SCHEMATIC
3
Friday, July 31, 2015
11
STEP-DOWN LED DRIVER WITH THREE-STATE CONTROL
ANTONINA K.
WALKER B.
A
LT3743EUFD
DEMO CIRCUIT 1470A
SIZE DATE:
IC NO.
REV
SHEET OF
TITLE:
CONTRACT NO.
APPROVALS
PCB DES.
ENG.
TECHNOLOGY Fax: [phone]
Milpitas, CA 95035 Phone: [phone] McCarthy Blvd. LTC Confidential-For Customer Use Only
CUSTOMER NOTICE
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL APPLICATION. COMPONENT SUBSTITUTION AND PRINTED CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY. CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
SCHEMATIC
3
Friday, July 31, 2015
11
STEP-DOWN LED DRIVER WITH THREE-STATE CONTROL
ANTONINA K.
WALKER B.
A
LT3743EUFD
DEMO CIRCUIT 1470A
SIZE DATE:
IC NO.
REV
SHEET OF
TITLE:
CONTRACT NO.
APPROVALS
PCB DES.
ENG.
TECHNOLOGY Fax: [phone]
Milpitas, CA 95035 Phone: [phone] McCarthy Blvd. LTC Confidential-For Customer Use Only
CUSTOMER NOTICE
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS; HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL APPLICATION. COMPONENT SUBSTITUTION AND PRINTED CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT PERFORMANCE OR RELIABILITY. CONTACT LINEAR TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
SCHEMATIC
3
Friday, July 31, 2015
11
STEP-DOWN LED DRIVER WITH THREE-STATE CONTROL
ANTONINA K.
WALKER B.
A
LT3743EUFD
DEMO CIRCUIT 1470A
E5
CTRL_L
E12
GND
C26 1.2nF
+
C18 470uF
R6 10k
+
C25 470uF
C1
4.7uF
R19
432K
R23
3.01K
R15 10
R5 51K
R2
374K
Q2
BSC080N03LS G
3
2
1
4
5
6
7
8
C8 1uF
+
C14 OPT
Q3
BSC011N03LSI
3
2
1
4
5
6
7
8
R17 0
R7 51K
R1 124K
R27
0
E7
CTRL_SEL
Q5
Si7234DP
3
4
1
27
8 6 5
E1
VIN
R21 OPT
U1
LT3743EUFD
EN/UVLO
2
VREF
3
CTRL_T
4
CTRL_H
6
CTRL_L
7
SS
8
GND
21
FB
10
SENSE+ 11
SENSE- 12
VCL 13
VCH 14
RT
15
SYNC
16
CTRL_SEL
17
PWM
18
PWMGH 19
PWMGL 22
HG 23
SW 24
CBOOT 25
LG 26
VCC_INT 27
VIN
28
GND
29
GND
5
GND
20
GND
1
GND
9
D1
PMEG4002EB
1 2
+
C23
470uF
C15
33nF
E13
IS+
R26
OPT
R20
100K
R16 10
C16
4.7uF
E11
LED-
+
C21 470uF
E8
SYNC
R3 0.0025
D2
DFLS240
OPT
R10
100K
L1
1.3uH
C27 10uF
R22 OPT
R11 OPT
E14
IS-
R13
100K
R4 100K
+
C11
100uf,50V
50CE100LX
R9
100K
R24 2K
R8 51K
Q1
3
2
1
4
5
6
7
8
E4
CTRL_H
+
C24 OPT
+
C19 OPT
+
C13 OPT
C17
E9
PVIN
6V - 36V
R25 OPT
C9 5.6nF
+
C22 OPT
C4
22uF
6.3V
+
C6 470uF
C7
2nF
R18
24.9K
E6
PWM Q6
Si7234DP
3
4
1
27
8 6 5
E2
EN/UVLO
R12
100K
C12
+
C20 OPT
E10
VOUT
*
Q4
OPT
3
2
1
4
5
6
7
8
R14 100K
C2 1uF 50V
C3
0.22uF
E3
GND
+
C5 470uF
C10
5.6nF

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dc1470af
DEMO MANUAL DC1470A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
 LINEAR TECHNOLOGY CORPORATION 2015
LT 0915 • PRINTED IN USA
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

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