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 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
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.
PERFORMANCE SUMMARY
SYMBOL
PV
IN
*
V
OUT
*
I
OUT
f
SW
I
RISE
EFF
PARAMETER
Input Supply Range, P
VIN
= V
IN
Output Voltage
Output Current
Switching Frequency
Current Rise Time
Efficiency at DC
Specifications are at T
A
= 25°C
CONDITIONS
L1 is Optimized for 12V
With One PT120 LED, 6V is the Over
Voltage Limit
CTRL_SEL > 1V
Following a PWM Rising Edge
V
IN
= 12V, V
OUT
= 5V, I
OUT
= 20A
18.8
400
MIN
TYP
12
4.5
20
430
2
94
MAX
26.4
6
21.2
460
UNITS
V
V
A
kHz
μs
%
*PV
IN
and V
IN
of the demo circuit are limited to 24V typical by the selection of MOSFETs. The LT3743 input range is 6V to 36V. V
OUT
maximum of the
demo circuit is limited to 6V due to the selection of the output capacitors.
dc1470af
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 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 PV
IN
and GND. The input power supply should have a current
limit of 10A or more.
2. With power off, connect a LED between V
OUT
and GND
or between V
OUT
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.
4. At this time, the output current will be slightly below
5A. If no output current is observed, turn off PV
IN
and
check the connections.
5. To increase the load current to 20A, turn off PV
IN
. 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 PV
IN
.
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.
2
dc1470af
DEMO MANUAL DC1470A
QUICK START PROCEDURE
Figure 1. Proper Measurement Equipment Setup
Figure 2. Measuring Voltage Across R25
IS+
IS–
dc1470af
3
DEMO MANUAL DC1470A
PARTS LIST
ITEM
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
1
2
3
4
5
1
2
3
QTY
4
1
1
1
6
1
1
2
1
1
1
1
1
1
1
2
1
2
1
1
1
7
3
1
2
1
1
1
1
1
0
0
2
0
0
10
4
4
REFERENCE
C1, C12, C16, C17
C2
C3
C4
C5, C6, C18, C21, C23, C25
C7
C8
C9,C10
C11
C15
C26
C27
D1
D2
L1
Q1,Q2
Q3
Q5,Q6
R1
R2
R3
R4, R9, R10, R12, R13, R14, R20
R5, R7, R8
R6
R15, R16
R18
R19
R23
R24
U1
C13, C14, C19, C20, C22, C24
R11, R21, R22, R26
R17, R27
R25
Q4 OPT
E1-E8, E13, E14
E9-E12
STAND-OFF
TURRET, TESTPOINT, 091"
JACK BANANA
STAND-OFF, NYLON 0.5" TALL
MILL MAX 2501-2-00-80-00-00-07-0
KEYSTONE, 575-4
KEYSTONE, 8833(SNAP ON)
dc1470af
PART DESCRIPTION
CAP., X7R, 4.7μF, 50V, 10%, 1210
CAP., X7R, 1μF, 50V, 10%,0805
CAP., X7R, 0.22μF, 10V,10%,0603
CAP., X5R, 22μF, 6.3V, 20%, 0805
CAP., POSCAP, 470μF, 6.3V, D4D
CAP., C0G, 2nF, 50V, 0603
CAP., X7R, 1μF, 16V, 10%,0603
CAP., C0G, 5600pF, 50V, 5% 0603
CAP., ALUM., ELECT., 100μF, 50V
CAP., X5R, 0.033μF, 50V, 0603
CAP., X7R, 1200pF, 50V,5%, 0603
CAP., X7R, 10μF, 25V,10%,1206
SCHOTTKY RECTIFIER, 40V, SOD523
2.0A LOW VF SCHOTTKY RECTIFIER
INDUCTOR, 1.3μH
N-CHANNEL MOSFET, LFPAK
N-CHANNEL MOSFET, LFPAK
MOSFET, 40V, DUAL N-CHANEL, PPAK
RES., CHIP, 124k, 1%, 1/W, 0603
RES., CHIP, 374k, 1%, 1/W, 0603
RES., CHIP, 0.0025Ω, 1W, 1%, 2512
RES., CHIP, 100k, 1%, 1/W, 0603
RES., CHIP, 51k, 1%, 1/W, 0603
RES., CHIP, 10k, 1%, 1/W, 0603
RES., CHIP, 10Ω, 1%, 1/W, 0603
RES., CHIP, 24.9k, 1%, 1/W, 0603
RES., CHIP, 432k, 1%, 1/W, 0603
RES., CHIP, 3.01k, 1%, 1/W, 0603
RES., CHIP, 2k, 1%, 1/W, 0603
I.C. LT3743EUFD, 28-PIN QFN-4×5
CAP., D4D, OPT
RES., OPT, 0603
RES., CHIP, 0Ω, 0603
RES., CHIP, 2512, OPT
MANUFACTURER/PART NUMBER
MURATA, GRM32ER71H475KA88L
MURATA, GRM21BR71H105KA12L
MURATA, GRM188R71A224KA01D
MURATA, GRM21BR60J226ME39L
PANSONIC, 6TPF470MAH
MURATA, GRM1885C1H202JA01
MURATA, GRM188R71C105KA12D
MURATA, GRM1885C1H562JA01D
SUN ELECTRONICS., 50CE100LX
AVX, 06035D333KAT2A
AVX, 06035C122JAT2A
MURATA, GRM31CR71E106KA12L
NXP SEMI., PMEG4002EB,115
DIODES INC., DFLS240L-7
WURTH ELECTRONICS, 7443551130
INFINEON, BSC080N03LS G
INFINEON, BSC011N03LSI
VISHAY, Si7234DP
VISHAY, CRCW0603124KFKEA
VISHAY, CRCW0603374KFKEA
VISHAY, WSL25122L500FEA
VISHAY, CRCW0603100KFKEA
VISHAY, CRCW060351K0FKEA
VISHAY, CRCW060310K0FKEA
VISHAY, CRCW060310R0FKEA
VISHAY, CRCW060324K9FKEA
VISHAY, CRCW0603432KFKEA
VISHAY, CRCW06033K01FKEA
VISHAY, CRCW06032K00FKEA
LINEAR TECH., LT3743EUFD#PBF
Required Circuit Components
Additional Demo Board Circuit Components
VISHAY, CRCW06030000Z0EA
Hardware for Demo Board Only
4
5
4
3
2
ECO
1
3
PRODUCTION
WALKER B.
10-02-09
REV
REVISION HISTORY
DESCRIPTION
APPROVED
DATE
1
VIN
*
*
PVIN
E9
6V - 36V
GND
E12
D
D
R17 0
VIN
5
6
7
7
8
Q2
4
BSC080N03LS G
1
2
2
3
R26
OPT
4.7uF
4.7uF
C16
C17
+
Q1
C11
100uf,50V
50CE100LX
C1
C12
VIN
*
R27
0
U1
23
LT3743EUFD
25
1
HG
28
VIN
VCC_INT
C4
22uF
6.3V
24
C19
OPT
1
C13
OPT
5
6
7
7
8
C18
470uF
+
+
6V - 36V
E1
SCHEMATIC DIAGRAM
GND
2
D1
PMEG4002EB
VCC_INT
R3
0.0025
27
L1
1.3uH
R1
124K
CBOOT
R2
374K
C2
1uF
50V
C3
0.22uF
E3
VOUT
*
E10
C5
470uF
C6
470uF
C14
OPT
1
+
+
EN/UVLO
EN/UVLO
VREF
SW
CTRL_T
CTRL_H
1
2
2
3
CTRL_L
4
VCC_INT
3
SENSE+
R15
R16
10
10
C15
33nF
11
R23
3.01K
PWM
CTRL_SEL
SYNC
SENSE-
8
SS
PWMGL
15
RT
GND
GND
GND
GND
GND
GND
FB
VCL
R8
51K
C10
5.6nF
13
R7
51K
C9
5.6nF
VCH
14
22
R12
100K
R13
100K
C8
1uF
PWMGH
19
12
LG
2
3
R21
OPT
R22
OPT
6
7
18
17
16
D2
DFLS240
OPT
8
7
5
6
Q5
Si7234DP
C7
2nF
4
Q3
BSC011N03LSI
Q4
OPT
4
26
R4
100K
2
E2
C21
470uF
C20
OPT
C27
10uF
LED-
E11
2
4
3
C
C
R18
24.9K
R19
432K
R20
100K
CTRL_H
E4
CTRL_L
8
7
5
6
Q6
Si7234DP
R25
OPT
IS+
E13
PWM
E5
E6
CTRL_SEL
E7
IS-
E14
C23
470uF
C22
OPT
+
+
SYNC
E8
C25
470uF
C24
OPT
R24
2K
R9
100K
R10
100K
R11
OPT
B
B
1
5
20
21
29
10
R14
100K
(400kHz)
9
R5
51K
C26
R6
10k
1.2nF
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.
* See Quick Start Guide
A
CUSTOMER NOTICE
CONTRACT NO.
TECHNOLOGY
SCHEMATIC
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.
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
LTC Confidential-For Customer Use Only
A
HIGH CURRENT SYNCHRONOUS
STEP-DOWN LED DRIVER WITH THREE-STATE CONTROL
SIZE
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
A
3
IC NO.
DATE:
Friday, July 31, 2015
4
2
DEMO CIRCUIT 1470A
1
LT3743EUFD
REV
3
SHEET
1 OF 1
5
DEMO MANUAL DC1470A
dc1470af
5
NXP MCU
