DC1470A - Demo Manual

DEMO MANUAL DC1470A
LT3743 High Current
Synchronous Step-Down LED
Driver with Three-State Control
DESCRIPTION
Demonstration circuit 1470A is a high current synchronous
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. Grounding cathode of the LED allows customers
to use positive input supply.
The input voltage range of the LT3743 itself is 6V to 36V.
However, the demo board utilizes 30V MOSFETs to demonstrate 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
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
Design files for this circuit board are available at
http://www.linear.com/demo/DC1470A
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.
Specifications are at TA = 25°C
SYMBOL
PARAMETER
CONDITIONS
PVIN*
Input Supply Range, PVIN = VIN
VOUT*
MIN
TYP
MAX
UNITS
L1 is Optimized for 12V
12
26.4
V
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.
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1
DEMO MANUAL DC1470A
DESCRIPTION
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.
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
toggle the output between 5A to 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
Demonstration circuit 1470A is easy to set up to evaluate 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.
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.
3.Turn on the power at the input.
2
dc1470af
DEMO MANUAL DC1470A
QUICK START PROCEDURE
Figure 1. Proper Measurement Equipment Setup
IS–
IS+
Figure 2. Measuring Voltage Across R25
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3
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
3
2
R17, R27
RES., CHIP, 0Ω, 0603
4
0
R25
RES., CHIP, 2512, OPT
5
0
Q4 OPT
VISHAY, CRCW06030000Z0EA
Hardware for Demo Board Only
4
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)
dc1470af
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.
A
B
C
VIN
*
SYNC
CTRL_SEL
PWM
CTRL_L
CTRL_H
EN/UVLO
GND
6V - 36V
E8
E7
E6
E5
E4
E2
E3
E1
5
R9
100K
R18
24.9K
R10
100K
R19
432K
R11
OPT
R20
100K
R12
100K
R21
OPT
R1
124K
R13
100K
C7
2nF
R2
374K
R4
C8
1uF
R14
100K
(400kHz)
R22
OPT
100K
C2
1uF
50V
VIN
15
8
16
17
18
7
6
4
3
2
28
RT
SS
SYNC
CTRL_SEL
PWM
CTRL_L
CTRL_H
CTRL_T
VREF
EN/UVLO
VIN
U1
LT3743EUFD
4
23
HG
25
CBOOT
VCL
VCH
PWMGL
PWMGH
SENSE-
SENSE+
LG
SW
VCC_INT
C4
22uF
6.3V
VCC_INT
C3
0.22uF
13
14
22
19
12
11
R8
51K
C15
33nF
3
10
R16
R7
51K
0.0025
R3
+
+
+
C24
OPT
C25
470uF
Si7234DP
Q5
R24
2K
A
SIZE
DATE:
IC NO.
OPT
1.2nF
C26
E14
E13
E11
DATE
*
IS-
IS+
LED-
VOUT*
GND
6V - 36V
PVIN
10-02-09
LT3743EUFD
1
DEMO CIRCUIT 1470A
SHEET
3
1 OF 1
REV
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
LTC Confidential-For Customer Use Only
R6
10k
R5
51K
E10
E12
E9
C27
10uF
Si7234DP
Friday, July 31, 2015
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
2
APPROVED
WALKER B.
R25
C20
OPT
C21
470uF
1
Q6
8
7
5
6
+
TECHNOLOGY
+
PRODUCTION
DESCRIPTION
REVISION HISTORY
HIGH CURRENT SYNCHRONOUS
STEP-DOWN LED DRIVER WITH THREE-STATE CONTROL
SCHEMATIC
4
2
C14
OPT
C13
OPT
8
7
5
6
C6
470uF
C5
470uF
C11
100uf,50V
50CE100LX
CONTRACT NO.
C22
OPT
C23
470uF
4
2
+
+
*
3
1
VIN
REV
ECO
R17 0
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A APPROVALS
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO PCB DES. ANTONINA K.
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
ENG. WALKER B. TITLE:
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
CUSTOMER NOTICE
R23
3.01K
VCC_INT
C19
OPT
C18
470uF
C1
C12
4.7uF
C16
C17
4.7uF
* See Quick Start Guide
C9
5.6nF
D2
DFLS240
OPT
L1
1.3uH
BSC080N03LS G
Q2
Q1
C10
5.6nF
10
R15
Q3
BSC011N03LSI
Q4
OPT
4
26
24
27
D1
PMEG4002EB
R27
0
4
R26
OPT
2
1
5
6
7
8
1
2
3
5
6
7
8
1
2
3
D
2
1
3
3
1
3
4
GND
1
GND
5
GND
9
GND
20
GND
21
GND
29
FB
10
5
A
B
C
D
DEMO MANUAL DC1470A
SCHEMATIC DIAGRAM
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5
DEMO MANUAL DC1470A
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
6
dc1470af
Linear Technology Corporation
LT 0915 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
●
FAX: (408) 434-0507 ● www.linear.com
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