Linear Technology LT3512 Quick setup guide

1
dc1803af
DEMO MANUAL DC1803A
DESCRIPTION
LT3512: Monolithic
High Voltage Isolated
Flyback Converter
Demonstration circuit 1803A is a monolithic high voltage
isolatedflybackconverterfeaturingtheLT
®
3512.Thedemo
circuit is designed for a 5V isolated output from an input
voltage range of 36V to 75V. The maximum output current
is 500mA. VIN can be lower if output current is less than
500mA. The circuit doesn’t require an opto-isolator due to
the output voltage being sensed directly from the primary
side transformer winding. A third winding is used to bias
the LT3512 for highest efficiency.
The flyback converter requires a minimum loading to
maintaingood regulation.A Zenerdiode isplaced between
VOUT+and VOUT–to clamp output voltage to ~7.5V if mini-
mum load requirement is not met. Depending on the input
voltage and the output regulation requirement, a 20mA to
30mA minimum load is usually sufficient.
The demo circuit uses a diode-Zener clamp to limit the
peak spike voltage due to transformer leakage inductance.
A diode-Zener clamp is more efficient than a RCD clamp.
The LT3512 operates in boundary mode and also provides
output voltage temperature compensation.
PERFORMANCE SUMMARY
(TA= 25°C)
The LT3512 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 1803A.
Design files for this circuit board are available at
http://www.linear.com/demo
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.
PARAMETER CONDITIONS VALUE UNITS
Minimum Input Supply Voltage 36 V
Maximum Input Supply Voltage 75 V
Output Voltage IOUT = 500mA 5 V
Output Voltage Tolerance IOUT = 500mA ±5 %
Switching Frequency VIN = 36V, IOUT = 500mA 160 kHz
VIN = 75V, IOUT = 500mA 240 kHz
Maximum Output Current 500 mA
Efficiency VIN = 36V, IOUT = 500mA 84 %
Figure 1. DC1803A Efficiency
LOAD CURRENT (mA)
50 100 150 250 300 400 450
0
EFFICIENCY (%)
10
30
40
50
350
90
DC1803A F01
20
200 500
60
70
80
VIN = 36V
VIN = 75V
VOUT = 5V
TA= 25°C

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dc1803af
DEMO MANUAL DC1803A
QUICK START PROCEDURE
Figure 2. Proper Measurement Equipment Setup
PARTS LIST
Demonstration circuit 1803A is easy to set up to evalu-
ate the performance of the LT3512. Refer to Figure 2 for
proper measurement equipment setup and to follow the
procedure below:
Note: When measuring the input or output voltage ripple, care must be
taken to avoid a long ground lead on the oscilloscope probe. Measure the
input or output voltage ripple by touching the probe tip directly across the
VIN and GND or VOUT+and VOUT–terminals.
Note: Make sure GND and VOUT–are not connected together accidently,
such as by two oscilloscope probes.
1. With power off, connect the input power supply to VIN
and GND.
2. Connect a load of 500mA or less to VOUT+and VOUT–
terminals (not GND).
3. Turn on the power at the input.
4. Check for the proper output voltage (5V).
Note: If there is no output, temporarily disconnect the load to make
sure that the load is not set too high.
5. Oncetheproperoutputvoltageisestablished,adjustthe
load and input within the operating ranges and observe
the output voltage regulation, ripple voltage, efficiency
and other parameters.
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
Required Circuit Components
1 1 C2 CAP., X7R, 1μF 100V, 10%, 1206 MURATA, GRM31CR72A105KA01L
2 1 C3 CAP., X5R, 47μF 10V, 10%, 1210 MURATA, GRM32ER61A476KE20L
3 1 C5 CAP., ELECT., 10μF 100V SUN ELEC., 100CE10BS
4 1 C9 CAP., X7R, 4.7μF 16V, 10%, 0805 TAIYO YUDEN, EMK212B7475KG
5 1 C10 CAP., X7R, 3300pF, 50V, 0402 AVX, 04025C332KAT2A
6 1 D1 DIODE, SCHOTTKY, SOD-123 DIODES INC SBR1A40S3
7 1 D2 DIODE, SOD-123 DIODES INC. BAV21W-7-F
8 1 D4 ZENER DIODE, SOD-123 ON SEMI., MMSZ5266BT1G
9 1 D5 ZENER DIODE, SOD-123 CENTRAL SEMI., CMHZ5236B TR
10 1 R3 RES., CHIP, 806k, 1%, 0805 VISHAY, CRCW0805806KFKEA
11 1 R4 RES., CHIP, 169k, 1%, 0603 VISHAY, CRCW0603169KFKEA

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dc1803af
DEMO MANUAL DC1803A
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However,noresponsibilityisassumed foritsuse.LinearTechnologyCorporationmakesnorepresentation
that the interconnection of its circuits as described herein will not infringe on existing patent rights.
PARTS LIST
SCHEMATIC DIAGRAM
ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER
12 1 R5 RES., CHIP, 31.6k, 5%, 0402 VISHAY, CRCW040231K6JNED
13 1 R6 RES., CHIP, 75k, 1%, 0402 VISHAY, CRCW040275K0FKED
14 1 R7 RES., CHIP, 16.9k, 1%, 0402 VISHAY, CRCW040216K9FKED
15 1 R8 RES., CHIP, 10k, 1%, 0402 VISHAY, CRCW040210K0FKED
16 1 T1 TRANSFORMER, 175μH WÜRTH ELEC., 750311559
17 1 U1 I.C., LT3512EMS, 16-PIN MSOP LINEAR TECH., LT3512EMS
Additional Demo Board Circuit Components
1 1 C6 CAP., X7R, 1000pF 2000V, 10%,1206 AVX 1206GC102KAT1A
2 0 C7 (OPT) CAP., 0402
3 1 D3 DIODE, SCHOTTKY, SOD-323 CENTRAL SEMI., CMDSH-3 TR
4 1 R9 RES., CHIP, 20, 1%, 0402 VISHAY, CRCW040220R0FKED
Hardware-For Demo Board Only
1 6 E1-E6 TESTPOINT, TURRET, 0.095" MILL-MAX, 2501-2-00-80-00-00-07-0
5
5
4
4
3
3
2
2
1
1
D D
C C
B B
A A
VOUT-
VIN
GND
+5V@500mA
VOUT+
36V - 75V
EN / UVLO
BIAS
Lp = 175uH
0805
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0805
(OPT)
1206 1210
1206
0603
VOUT+
BIAS
VOUT-
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5(9,6,21+,6725<
'(6&5,37,21 '$7($33529('(&2 5(9
:$/.(5%
352'8&7,21 
BB
5(9,6,21+,6725<
'(6&5,37,21 '$7($33529('(&2 5(9
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:$/.(5%
352'8&7,21 
BB
D2
BAV21W
D2
BAV21W
2 1
C3
47uF
10V
C3
47uF
10V
C7
(OPT)
C7
(OPT)
R4 169KR4 169K
U1
LT3512EMS
U1
LT3512EMS
EN/UVLO
1
SW 16
VIN 3
TC
11
BIAS 6
RFB 14
GND
5
GND
8
GND
9
VC
10
RREF
12
NC
7
E4E4
C10
3300pF
C10
3300pF
R5
31.6K
R5
31.6K
R6
75K
R6
75K
D3
CMDSH-3
D3
CMDSH-3
21
E5E5
D1 SBR1A40S3D1 SBR1A40S3
2 1
C9
4.7uF
16V
C9
4.7uF
16V
E6E6
R9 20 R9 20
R8
10K
R8
10K
C2
1uF
100V
C2
1uF
100V
C6
1000pF
2000V
C6
1000pF
2000V
T1
750311559
T1
750311559
3
4
8
5
2
1
6
7
E3E3
E1E1
D4
MMSZ5266BTIG
D4
MMSZ5266BTIG
21
R3
806K
R3
806K
+C5
10uF
100V
+C5
10uF
100V
R7
16.9K
R7
16.9K
E2E2
D5
CMHZ5236B
D5
CMHZ5236B
2 1

4
dc1803af
DEMO MANUAL DC1803A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
[phone] ●FAX: [phone] ●www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2011
LT 0411 • PRINTED IN USA
DEMONSTRATION BOARD IMPORTANT NOTICE
Linear Technology Corporation (LTC) provides the enclosed product(s) under the following AS IS conditions:
Thisdemonstrationboard(DEMOBOARD)kitbeing sold or provided byLinearTechnologyisintendedfor 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 direc-
tive 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 applica-
tion engineer.
Mailing Address:
Linear Technology
1630 McCarthy Blvd.
Milpitas, CA 95035
Copyright © 2004, Linear Technology Corporation

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