DEMO MANUAL DC1602A
LT3741
High Power Constant Current, Constant
Voltage Synchronous Buck Controller
Description
Demonstration circuit 1602A is a high power constant
current, constant voltage synchronous buck controller
featuring the
LT
®
3741.
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. The voltage limit on
this demo board is set to around 6V by R11 and R14. The
6V is chosen because of the 10V voltage rating of the output
capacitors. Higher output voltage can be easily achieved
with higher voltage rated 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.
The input voltage range of the LT3741 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. 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. Output current can
be adjusted by varying the CTRL1 voltage.
R16 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.
R10, R13 and C14 help filtering out voltage spikes seen
on the SENSE
+
or SENSE
–
pin. It is critical to have those
components on a board.
The LT3741 data sheet gives a complete description of
the part, operation and application information. The data
sheet must be read in conjunction with this quick start
guide for demo circuit 1602A.
Design files for this circuit board are available at
http://www.linear.com/demo/DC1602A.
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
V
OUT
F
SW
EFE
PARAMETER
Input Supply Range. PV
IN
= V
IN
Output Voltage
Output Current
Output Voltage
Switching Frequency
Efficiency at DC
Specifications are at T
A
= 25°C
CONDITIONS
L1 is Optimized for 12V.
With ONE PT120 LED. 6V Is the Overvoltage
Limit
In Current Mode
In Voltage Mode
R3 = 100k
V
IN
= 12V, V
OUT
= 5V, I
OUT
= 20A
18.8
5.88
380
MIN
TYP
12
4.5
20
6
420
94
MAX
24
6
21.2
6.12
460
UNITS
V
V
A
V
kHz
%
* PV
IN
and V
IN
of the demo circuit are limited to 24V typical by the selection of MOSFETs. The LT3741 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.
dc1602af
1
DEMO MANUAL DC1602A
Quick start proceDure
Demonstration circuit 1602A is easy to set up to evalu-
ate the performance of the LT3741. 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.
3. Turn on the power at the input. Be careful not to look
at a powered LED directly.
4. Carefully evaluate other design parameters as needed.
5. Adjust CTRL1 to change output current.
6. To modify the demo board for other applications, please
contact Linear Applications Group for help.
–
+
+
–
–
LOAD
+
DC1602 F01
Figure 1. Proper Measurement Equipment Setup
2
dc1602af
DEMO MANUAL DC1602A
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
QTY
1
4
2
1
1
2
1
1
1
1
1
1
1
1
2
1
1
1
3
1
1
2
1
1
1
1
1
REFERENCE
C1
C2, C3, C4, C5
C8, C10
C6
C7
C9, C11
C12
C13
C14
C15
C17
D1
D2
L1
Q1, Q2
Q3
R1
R2
R3, R5, R8
R4
R7
R10, R13
R11
R12
R14
R15
U1
PART DESCRIPTION
CAP ALUM., ELECT., 100µF, 50V
.,
CAP X7R, 4.7µF, 50V, 10%, 1210
.,
CAP POSCAP 150µF, 10V
.,
,
CAP X7R, 1µF, 50V, 10%, 0805
.,
CAP X7R, 0.22µF, 10V, 10%, 0603
.,
CAP X5R, 47µF, 16V, 10%, 1210
.,
CAP X5R, 22µF, 6.3V, 20%, 0805
.,
CAP COG, 2nF, 50V, 0603
.,
CAP NPO, 33nF, 16V, 0603
.,
CAP X7R, 10000pF, 16V, 0603
.,
CAP U2J, 5100pF, 50V, 0603
.,
1.0A LOW VF SCHOTTKY RECTIFIER
2.0A LOW VF SCHOTTKY RECTIFIER
INDUCTOR, 1.3µH
MOSFET, N-CHANNEL, PG-TDSON-8
MOSFET, N-CHANNEL, PG-TDSON-8
RES., CHIP 374k, 1%, 0603
,
RES., CHIP 124k, 1%, 0603
,
RES., CHIP 100k, 1%, 0603
,
RES., CHIP 0.0025, 1W, 1%, 2512
,
RES., CHIP 45.3k, 1%, 0603
,
RES., CHIP 10Ω, 1%, 0603
,
RES., CHIP 40.2k, 1%, 0603
,
RES., CHIP 680k, 1%, 0603
,
RES., CHIP 10k, 1%, 0603
,
RES., CHIP 66.5k, 1%, 0603
,
I.C. LT3741EFE, 20-PIN TSSOP
MANUFACTURER/PART NUMBER
SUN ELECT., 50CE100LX
MURATA, GRM32ER71H475KA88L
SANYO, 10TPF150ML
MURATA, GRM21BR71H105KA12L
MURATA, GRM188R71A224KA01D
MURATA, GRM32ER61C476KE15L
MURATA, GRM21BR60J226ME39L
MURATA, GRM1885C1H202JA01D
MURATA, GRM188R71C333KA01D
MURATA, GRM188R71C103KA01D
MURATA, GRM1887U1H512JA01D
DIODES INC., DFLS140
DIODES INC., DFLS240L
WE., 7443551130
INFINEON, BSC080N03LS G
INFINEON, BSC011N03LSI
VISHAY, CRCW0603374KFKEA
VISHAY, CRCW0603124KFKEA
VISHAY, CRCW0603100KFKEA
VISHAY, WSL25122L500FEA
VISHAY, CRCW060345K3FKEA
VISHAY, CRCW060310R0FKEA
VISHAY, CRCW060340K2FKEA
VISHAY, CRCW0603680KFKEA
VISHAY, CRCW060310K0JNEA
VISHAY, CRCW060366K5FKEA
LINEAR TECH., LT3741EFE#PBF
Required Circuit Components
dc1602af
3
DEMO MANUAL DC1602A
parts List
ITEM
1
2
3
4
1
2
3
QTY
0
0
1
0
4
6
4
REFERENCE
C16, C18
Q4
R16
R9, R17
E1, E2, E4, E5
E3, E6, E7, E8, E9, E10
STAND-OFF
PART DESCRIPTION
CAP 0603, OPT
.,
MOSFET, OPT
RES., CHIP 0Ω, 0603
,
RES., 1206, OPT
JACK, BANANA
TURRET, TESTPOINT , 091"
STAND-OFF NYLON, 0.5" tall
,
KEYSTONE, 575-4
MILL MAX 2501-2-00-80-00-00-07-0
KEYSTONE, 8833(SNAP ON)
VISHAY, CRCW06030000Z0ED
MANUFACTURER/PART NUMBER
Additional Demo Board Circuit Components
Hardware: For Demo Board Only
4
dc1602af
5
4
3
2
ECO
__
2
2-1
1-6-16
VIN
REBUILD CHANGED Q1,Q2,Q3
WALKER B.
PRODUCTION
WALKER B.
02-02-10
REV
REVISION HISTORY
DESCRIPTION
APPROVED
DATE
1
VIN
*
C2
C3
4.7uF
1210
C6
1uF
50V
0805
VIN
C4
C5
4.7uF
1210
D
6V - 36V
E1
D
+
C1
100uF,50V
50CE100LX
GND
E2
GND
U1
LT3741EFE
3
BSC080N03LS G
HG
CBOOT
2
D1
DFLS140
1
VCC_INT
C12
22uF
0805
R17
OPT
1206
C18
OPT
18
2
1
C9
C11
47uF
1210
19
1
1
2
3
R16
0
C7
0.22uF
17
R4
0.0025
2512
E4
C8
C10
150uF
E5
4
L1
1.3uH
WE 7443551130
5
6
6
7
8
4
R3
100K
14
RT
R5
100K
15
SYNC
EN/UVLO
VIN
Q1
Q2
VIN
schematic Diagram
E9
EN/UVLO
R1
374K
E3
R2
124K
VOUT
*
20A @ 6V
C
C
GND
SYNC
5
VREF
SW
5
5
6
7
7
8
Q3
BSC011N03LSI
Q4
OPT
D2
DFLS240L
4
1
2
2
3
1
E8
GND
E10
C13
2nF
R7
45.3K
8
CTRL1
LG
R9
OPT
6
CTRL2
SS
VC
21
GND
16
7 GND
2 GND
GND
FB
10
SENSEN
12
R13
10
9
C15
10nF
13
R15
66.5K
C17
5nF
C14
33nF
R10
10
R12
680K
SENSEP
11
20
R8
100K
CTRL1
E6
CTRL2
B
E7
R11
40.2K
B
C16
R14
10k
OPT
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.
A
NOTE: UNLESS OTHERWISE SPECIFIED
CUSTOMER NOTICE
APPROVALS
A.K.
WALKER B.
*
- SEE QUICK START GUIDE
TECHNOLOGY
TITLE: SCHEMATIC
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
www.linear.com
Fax: (408)434-0507
LTC Confidential-For Customer Use Only
LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A
CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;
HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO PCB DES.
VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL
APPLICATION. COMPONENT SUBSTITUTION AND PRINTED
APP ENG.
CIRCUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT
PERFORMANCE OR RELIABILITY. CONTACT LINEAR
TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.
A
1. ALL RESISTORS ARE IN OHMS, 0603.
ALL CAPACITORS ARE IN MICROFARADS, 0603.
HIGH POWER CONSTANT CURRENT,
CONSTANT VOLTAGE SYNCHRONOUS BUCK CONTROLLER
SIZE
THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND
SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.
N/A
SCALE = NONE
3
2
IC NO.
DATE:
Thursday, January 07, 2016
DEMO CIRCUIT 1602A
1
LT3741EFE
REV.
2-1
SHEET 1
OF 1
5
4
DEMO MANUAL DC1602A
dc1602af
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