Linear Technology LT3748 Quick setup guide

dc1694bfa

DEMO MANUAL DC1694B

DESCRIPTION

LT3748

100V Isolated

Flyback Converter

Demonstration circuit 1694B is an isolated flyback con-

verter featuring the LT

3748. The demo circuit is designed

for a 12V output from a 22V to 75V DC input. The output

current is up to 2.5A. The part senses the isolated output

voltage directly from the primary side flyback waveform

during the off time of the power switch. No third winding,

opto-coupler, or signal transformer is required for regula-

tion. A minimum load of approximately 2% of maximum

load is required on the output to maintain regulation.

The demo circuit can be easily modified for applications

of different input, and output voltage/current, with some

pre-designed transformers from vendors such as Würth

Electronics, Sumida, Pulse Engineering and Coilcraft. Both

EP13 and EFD20 core transformers can be assembled on

the board. A two-stage filter is optional for applications

requiring very small output ripple.

PERFORMANCE SUMMARY

The LT3748 is a high input voltage isolated flyback con-

troller operating with input supply voltages from 5V to

100V, and 1.9A average gate drive source and sink current.

The LT3748 utilizes boundary mode operation to provide

a high efficiency, small size solution with improved load

regulation of ±5% over the full line, load and temperature

ranges. The LT3748 can be used in a wide variety of indus-

trial,automotive,medical,telecom,data-comapplications,

where regulated isolated output is required.

The LT3748 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 1694B.

Design files for this circuit board are available at

http://www.linear.com/demo/DC1694B

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 MIN TYP MAX UNITS

Input Voltage Range 22 48 75 V

Output Voltage VIN = 22V to 75V

IOUT = 50mA to 2.5A

11.4 12 12.6 V

Maximum Output Current VIN = 22V to 75V 2.5 A

Output Voltage Ripple (Peak-to-Peak) VIN = 22V to 75V, IOUT = 2.5A 420 mV

Switching Frequency VIN = 48V, IOUT = 2.5A 289 kHz

Efficiency VIN = 48V, IOUT = 2.5A 86.5 %

Specifications are at TA= 25°C

dc1694bfa

DEMO MANUAL DC1694B

QUICK START PROCEDURE

Demo circuit 1694B is easy to set up to evaluate the

performance of the LT3748. Refer to Figure 1 for proper

measurement equipment setup and follow the procedure

below.

1. With power off, connect the input power supply to VIN

and GND.

2. Connect the load to the terminals VOUT+ and VOUT– on

the board. Apply a load between 100mA to 2.5A to the

output.

3. Turn on the power at the input. Increase VIN to 22V.

NOTE: Make sure that the input voltage does not exceed

75V.

4. Check for the proper output voltages. The output should

be regulated at 12V (±5%).

NOTE: If there is no output, temporarily disconnect

the power supply. Make sure that the load is properly

connected. If the output voltage is out of spec, make

sure minimum load current is applied to the output,

the load is not set too high, and the DC power supply

does not hit the current limit.

NOTE: If higher operating voltage is required, power

componentswithhigher voltage ratings should be used.

NOTE: The LT3748 requires minimum load to maintain

good regulation. A Zener diode D4 is placed between

VOUT+ and VOUT– to clamp the output voltage to ~13V

if minimum load requirement is not met. Depending on

input voltage and output regulation, a 100mA minimum

load is usually sufficient.

5. Oncethe proper output voltage isestablished,adjust the

input and load within the operating range and observe

the output voltage regulation, ripple voltage, efficiency

and other parameters.

NOTE: When measuring the input or output voltage

ripples, 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. See

Figure 2 for proper scope probe technique.

dc1694bfa

DEMO MANUAL DC1694B

QUICK START PROCEDURE

Figure 1. Proper Measurement Equipment Setup

Figure 2. Proper Scope Probe Placement for Measuring Input or Output Ripple

INPUT OR OUTPUT CAPACITOR

dc1694bfa

DEMO MANUAL DC1694B

PARTS LIST

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART #

Required Circuit Components

1 1 C1 CAP., ELECTRO., 100µF, 100V CHEMI-CON, EMVY101ARA101MKE0S

2 2 C2, C3 CAP., X7R, 2.2µF, 100V, 20% 1210 TDK C3225X7R2A225M

3 1 C6 CAP., X7R, 1.0µF, 100V, 20% 1206 AVX, 12061C105MAT2A

4 1 C7 CAP., X7R, 0.1µF, 16V, 10% 0402 TDK, C1005X7R1C104K

5 1 C8 CAP., C0G, 470pF, 50V, 5% 0402 TDK, C1005COG1H471J

6 1 C9 CAP., X5R, 4.7µF, 16V, 20% 0805 AVX, 0805YD475MAT2A

7 1 C10 CAP., C0G, 220pF, 100V, 5% 0805 AVX, 08051A221JAT2A

8 1 C11 CAP., X7R, 22nF, 25V, 10% 0402 MURATA, GRM155R71E223KA61D

9 1 C12 CAP., X7R, 2200pF, 250V, 10% 1812 MURATA, GA343QR7GD222KW01L

10 3 C16, C17, C18 CAP., X7R, 22µF,16V, 20% 1210 TDK, C3225X7R1C226M

11 1 C20 CAP., COG, 270pF, 100V, 5% 0805 MURATA, GRM2165C2A271JA01D

12 1 D1 DIODE., PDS5100, Power DI-5 DIODE INC., PDS5100-13

13 1 D3 Schottky Barrier Rec., BAT41, SOD523 ST, BAT41KFILM

14 1 D4 ZENER DIODE, DFLZ13, 13V, PowerDI-123 DIODE INC., DFLZ13-7

15 1 Q1 N-MOSFET, SI7450DP, PowerPAK VISHAY, SI7450DP-T1-GE3

16 1 R1 RES., CHIP, 12.1k, 1% 0402 VISHAY, CRCW040212K1FKED

17 1 R3 RES., CHIP, 402k, 1% 0402 VISHAY, CRCW0402402KFKED

18 1 R5 RES., CHIP, 6.04k, 1% 0402 NIC, NRC04F6041TRF

19 1 R6 RES., CHIP, 32.4k, 1% 0402 VISHAY, CRCW040232K4FKED

20 1 R7 RES., CHIP, 150k, 1% 0603 VISHAY, CRCW0603150KFKED

21 2 R8, R13 RES., CHIP, 0, 1% 0603 VISHAY, CRCW06030000Z0EA

22 1 R9 RES., CHIP, 63.4k, 1% 0402 VISHAY, CRCW040263K4FKED

23 1 R10 RES., CHIP, 0.015Ω, 1/8W, 1% 0805 VISHAY, WSL0805R015F

24 2 R11, R12 RES., CHIP, 43Ω, 1/4W, 5% 1206 VISHAY, CRCW120643R0JNEA

25 1 R14 RES., CHIP, 10, 1% 0603 VISHAY, CRCW060310R0FKED

26 1 R15 RES., CHIP, 22, 1/8W, 5% 0805 VISHAY, CRCW080522R0JNEA

27 1 T1 TRANSFORMER Midcom, Inc. 750311607

28 1 U1 I.C. LT3748EMS, MSOP-16 LINEAR TECH., LT3748EMS#TRPBF

Additional Demo Board Circuit Components

1 0 C4, C5, C13, C14, C15 ( OPT.) CAP., 1210

2 0 C19 (OPT.) CAP., 0603

3 0 D5 (OPT.) Schottky Barrier Rec., SOD-323

4 0 L1 (OPT.) INDUCTOR

5 0 ROUT (OPT.) RES., 1210

Hardware – For Demo Board Only

1 4 E1, E2, E5, E6 TESTPOINT, TURRET, .094” pbf MILL-MAX, 2501-2-00-80-00-00-07-0

2 1 JP1 3 PIN 0.079 SINGLE ROW HEADER SAMTEC, TMM103-02-L-S

3 1 XJP1 SHUNT, .079” CENTER SAMTEC, 2SN-BK-G

4 4 MTG 4 CORNERS STAND-OFF, NYLON (SNAP ON), 0.25” TALL KEYSTONE, 8831

dc1694bfa

DEMO MANUAL DC1694B

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.

Figure 3. DC1694B Demo Circuit Schematic

SCHEMATIC DIAGRAM

NOTE: UNLESS OTHERWISE SPECIFIED

1. ALL RESISTORS ARE 0402.

ALL CAPACITORS ARE 0402.

VOUT-

VOUT+

22V - 75V

12V / 2.5A

750311607

1210

VIN

GND

E1E1

LT3748EMS

VIN1

EN/UVLO

SENSE 7

INTVCC 5

GATE 6

RFB 16

RREF

GND

0.1uF

C16

16V

22uF

C16

16V

22uF

C17C17

C13

1210

C13

1210

C18C18

6.04K

22nF

C11

22nF

C11

BAT41KFILM

SOD523

BAT41KFILM

SOD523

PDS5100

0.47uH

OPT.

0.47uH

OPT.

1210

OPT

1210

OPT

JP1

SHDN

JP1

SHDN

E5E5

E2E2

100V

2.2uF

1210

100V

2.2uF

1210

470pF

C15

OPT

C15

OPT

SI7450DP

67 8

C3C3

OPT.

R14

0603

R14

0603

270pF

C20

100V

0805

270pF

C20

100V

0805

C5C5

150K

0603

150K

0603

Midcom

VOPTVOPT

4.7uF

16V

0805

4.7uF

16V

0805

ROUT

OPT

1210

ROUT

OPT

1210

R12

43 1206

R12

43 1206

R11

43 1206

R11

43 1206

R10

0.015

0805

R10

0.015

0805

63.4K

C12

1812

250V

2200pF

C12

1812

250V

2200pF

C19

OPT.

0603

C19

OPT.

0603

C10

220pF 0805

100V

C10

220pF 0805

100V

R8 0

0603

R8 0

0603

12.1k

DFLZ13

13V

DFLZ13

13V

C14C14

100uF

100V

100uF

100V

32.4k

402k

E6E6

1uF

1206

100V

1uF

1206

100V

R15

22 0805

R15

22 0805

R13 0

0603

R13 0

0603

dc1694bfa

DEMO MANUAL DC1694B

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ●FAX: (408) 434-0507 ●www.linear.com

 LINEAR TECHNOLOGY CORPORATION 2012

LT 0914 • PRINTED IN USA

DEMONSTRATION BOARD IMPORTANT NOTICE

Linear Technology Corporation (LT C ) 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 LT C 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 LT C 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. LT C assumes no liability for applications assistance,

customer product design, software performance, or infringement of patents or any other intellectual property rights of any kind.

LT C 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 LT C applica-

tion engineer.

Mailing Address:

Linear Technology

1630 McCarthy Blvd.

Milpitas, CA 95035

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