Linear Technology LTC3725 Manual de usuario

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

LTC3725 / LTC3726

DESCRIPTION

Demonstration circuit 1031A-C is a 36V-72Vin, syn-

chronous forward converter featuring the

LTC3725/LTC3726. This circuit was designed spe-

cifically to attain a high current, low ripple, synchro-

nously rectified forward to efficiently power 5.0V

loads at up to 20A from a typical telecom input volt-

age range. This circuit features secondary-side con-

trol of the supply eliminating the need for an opto-

coupler, self-starting architecture, input undervoltage

lockout, and output overvoltage protection.

Design files for this circuit board are available.

Call the LTC factory.

,LTC and LT are registered trademarks of Linear Technology Corporation.

Table 1.

Performance Summary (TA= 25°C)

PARAMETER CONDITION VALUE

Minimum Input Voltage 36V

Maximum Input Voltage 72V

Output Voltage V

OUT

= 36V to 72V, I

OUT

= 0A to 20A 5.0V

Maximum Output Current 200LFM Airflow 20A

Typical Output Ripple V

OUT

= 72V, I

OUT

= 20A 100mV

P–P

Size Component Area x Top Component Height 2.3” x 0.9” x 0.394”

Peak Deviation with Load Step of 10A to 20A (10A/us) ±200mV

Load Transient Response

Settling Time 40us

Nominal Switching Frequency 300kHz

Efficiency V

= 48V, I

OUT

= 20A 91.5% Typical

OPERATING PRINCIPLES

The LTC3726 controller is used on the secondary and

the LTC3725 driver with self-starting capability is

used on the primary. When an input voltage is ap-

plied, the LTC3725 begins a controlled soft-start of

the output voltage. As this voltage begins to rise, the

LTC3726 secondary controller is quickly powered up

via T1, D1, and Q27. The LTC3726 then assumes

control of the output voltage by sending encoded

PWM gate pulses to the LTC3725 primary driver via

the small signal transformer, T2. The LTC3725 then

operates as a simple driver receiving both input sig-

nals and bias power through T2.

The transition from primary to secondary control oc-

curs seamlessly at a fraction of the output voltage.

From that point on, operation and design simplifies to

that of a simple buck converter. Secondary sensing

eliminates delays, tames large-signal overshoot and

reduces output capacitance while utilizing off-the-

shelf magnetics and attaining high efficiency.

For large values of input inductance, a 100V, 47uF elec-

trolytic capacitor can be added across the input termi-

nals to damp the input filter and provide adequate stabil-

ity. See Linear Technology Application Note AN19 for a

discussion on input filter stability analysis. A recom-

mended part is the Sanyo 100MV39AX.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

QUICK START PROCEDURE

Demonstration circuit 1031A-C is easy to set up to

evaluate the performance of the LTC3725/LTC3726.

Refer to Figure 1 for proper measurement equipment

setup and 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 output (or

input) voltage ripple by touching the probe tip and

probe ground directly across the input or output ca-

pacitor. See Figure 2 for proper scope probe tech-

nique.

Set an input power supply that is capable of 36V to

72V at a current of at least 3.5A to a voltage of 36V.

Then, turn off the supply.

With power off, connect the supply to the input

terminals +Vin and –Vin.

Input voltages lower than 36V can keep the con-

verter from turning on due to the undervoltage

lockout feature of the LTC3725/LTC3726.

If efficiency measurements are desired, an am-

meter capable of measuring 3.5Adc can be put

in series with the input supply in order to meas-

ure the DC1031A-C’s input current.

A voltmeter with a capability of measuring at

least 72V can be placed across the input termi-

nals in order to get an accurate input voltage

measurement.

Turn on the power at the input.

NOTE:

Make sure that the input voltage never ex-

ceeds 72V.

Check for the proper output voltage of 5.0V

Turn off the power at the input.

Once the proper output voltages are established,

connect a variable load capable of sinking 20A at

5.0V to the output terminals +Vout and –Vout. Set

the current for 0A.

If efficiency measurements are desired, an am-

meter or a resistor current shunt that is capable

of handling at least 20Adc can be put in series

with the output load in order to measure the

DC1031A-C’s output current.

A voltmeter with a capability of measuring at

least 5.0V can be placed across the output ter-

minals in order to get an accurate output voltage

measurement.

Turn on the power at the input.

NOTE:

If there is no output, temporarily disconnect

the load to make sure that the load is not set too

high.

Once the proper output voltage is established, ad-

just the load within the operating range and ob-

serve the output voltage regulation, ripple voltage,

efficiency and other desired parameters.

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Figure 1.

Proper Measurement Equipment Setup

Figure 2.

Measuring Input or Output Ripple

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

MEASURED DATA

Figures 3 through 11 are measured data for a typical DC1031A-C. Figures 12 through 21 are schematics, bill of mate-

rials and layout.

Figure 3.

Efficiency (200lfm airflow)

Figure 4.

Output Ripple Voltage (72Vin, 20Aout)

50mV/div

1us/div

86

88

90

92

94

6 8 10 12 14 16 18 20

LOAD CURRENT (A)

EFFICIENCY (%)

36V

48V

72V

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Figure 5.

Output Voltage Transient Response (48Vin, 10A to 20A step)

Vout

200mV/DIV

Iout

10A/div

20us/DIV

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Figure 6.

Temp Data (48Vin, 20A, 25



C, 200LFM airflow – front)

Figure 7.

Temp Data (48Vin, 20A, 25



C, 200LFM airflow – back)

Figure 8.

Temp Data (36Vin, 20A, 25



C, 200LFM airflow – front)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Figure 9.

Temp Data (36Vin, 20A, 25



C, 200LFM airflow – back

Figure 10.

Temp Data (72Vin, 20A, 25



C, 200LFM airflow – front)

Figure 11.

Temp Data (72Vin, 20A, 25



C, 200LFM airflow – back)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Figure 12.

Simplified Schematic

PT-

C31,C33

2x100uF

6.3V

124K

VIN

LINEAR TECHNOLOGY CORPORATION

CONFIDENTIAL

THIS CIRCUIT IS DISTRIBUTED

TO CUSTOMERS ONLY FOR USE

WITH LTC PARTS.

100

-VOUT

23.4 x 20.1 x 9.4mm PLANAR

115

3 9

R46

604

C81

10pF

+Vout

LTC3726EGN

IT H

S W

FB/PH

G ND

IS +

IS -

S G

V CC

PT+

PT-

S LP

F S/S Y NC

RUN /S S

M O DE

P G ND

R79

510

R69

-Vout

1.5nF

VCC

R63

330pF

C70

VSW

100

R54

R85

C79

2.2nF

CMPSH1-4

R89

536

1.2

1/4W

C27

330pF

+Vin

0.022

1.0uF

100V

C29

33nF

C75

47pF

-Vin

1uF,100V TDK C3225X7R2A105M (1210)

100uF, 6.3V CER TDK C3225X5R0J107M (1210)

C68 Sanyo 6TPE220MI

C30 Murata GA343QR7GD222KW01L (1812)

L1 Vishay IHLP-2525CZER1R0M-01

L2 Cooper HC1-R87

T1 PA0811 (4:4:2:1)

T2 Pulse PA0297 2(1.4mH):1:1

C3,C4,C5

100V

3x1.0uF

C77

2.2uF

36-72Vin

-VOUT

100

R55

Q27

FCX491

Si7336ADP

Q14

3.01K

Si7336ADP

Q12

D29

1N4148W

R76

1/4W

C72

0.1uF

5.0V/20A

VIN

C55

470pF

-VOUT

C78

33nF

LINE AR TECHNO LOGY HAS MADE A BEST EF FO RT T O DESIGN A CIRCUIT

THA T MEET S CUST OME R-SUPPLIED SPECIFICAT IONS; HOWEVER, IT

REMAINS THE CUSTOMER'S RESPO NSIBILIT Y T O VERIFY PRO PER AND

RELIABLE OPERATIO N IN THE ACT UAL APPLICAT ION. CO MPONENT

SUBSTIT UTION AND PRINT ED CIRUIT BOARD LAYO UT MAY SIG NIF ICANTLY

AFF ECT CIRCUIT PERF ORMANCE OR RELIABILIT Y. CONTACT LINEAR

TECHNOLOGY APPLICAT IONS ENG INEERING FO R ASSIST ANCE.

R61

100

C67

25V

4.7uF

PT-

C73

470pF

R18

365K

R66

100K

C68

220uF

6.3V

1uH

C24

1uF

(SOT6)

C30

2.2nF

250V

R22

15.0K

FDC2512

Q28

VSW

R58

5.1K

LTC3725EMSE

NDRV

VCC

V S LMT

G A T E

SSFLT

FB/IN+

FS/IN-

ULVO

P G ND

G ND

Q34

2N7002

R51

2.4

1/4W

C71

1uF

(SOT89)

R48

CUSTOMER NOTICE

4.42K

R29

100K

-VOUT R41

C66

1nF

200V

D28

MMBZ5236B

7.5V

C69

50V

R50

0.002

Si7450DP

R68

6.2K

0.87uH

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Figure 13.

Full Board Schematic

R54

100

opt.

For All The Versions

C2-C5 1uF,100V TDK C3225X7R2A105M (1210)

C31,C33 100uF, 6.3V CER TDK C3225X5R0J107M (1210)

C68 Sanyo 6TPE220MI

L1 Vishay IHLP-2525CZER1R0M-01 or

COOPER HCP0703-1R0-R

L2 Coil Tronics HC1-R87

T2 Pulse PA0297 2(1.4mH):1:1

100

C69

50V

PT-

R66

100K

R18

365K

opt

R68

6.2K

R63

R56

opt.

R87

C33

100uF

6.3V

3.3V/20A

R46

604

C31

100uF

6.3V

Q28

FDC2512

4 1

-Vout

160K

PA0815(6:6:2:1)

+VOUT

C70

330pF

R49

R69

R58

5.1K

D29

1N4148W

2.5V/20A

CMPSH1-4

DC1031A

Wednesday , August 23, 2006

J. WU 12/5/05

K. Mathews 12/5/05

LTC3725EMSE, LTC3726EGN, 36V - 72Vin Forward Converter

SIZE

SCALE:

CAGE CODE DWG NO REV

SHEET OF

FILENAME:

TITLE

CONTRACT NO.

APPROVALS DATE

DRAWN

CHECKED

APPROVED

ENGINEER

DESIGNER

TECHNOLOGY

1630 McCarthyBlvd.

Milpitas, CA95035

Phone: (408)432-1900

Fax: (408)434-0507

THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND

SUPPLIED FOR USEWITH LINEAR TECHNOLOGY PARTS.

LINEAR TECHNOLOGY HAS MADEA BEST EFFORT TO DESIGN A

CIRCUIT THAT MEETSCUSTOMER-SUPPLIED SPECIFICATIONS;

HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO

VERIFYPROPER AND RELIABLEOPERATION IN THE ACTUAL

APPLICATION. COMPONENT SUBSTITUTION AND PRINTED

CIRUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT

PERFORMANCE OR RELIABILITY. CONTACT LINEAR

TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.

CUSTOMER NOTICE

R41

R52

opt.

1/4W

R51

2.4

1/4W

D25

LTC3725EMSE

NDRV

VCC

VSLMT

GATE

SSFLT

FB/IN+

FS/IN-

ULVO

PGND

GND

1.5nF

VSW

R48

C81

10pF

Vout/Iout

C79

2.2nF

910

R89

Q11

opt.

2 3

6 7 8

100K5.0V/20A

-VOUT

Si7450DP

2 3

6 7 8

4.42K PA0811(4:4:2:1)

VCC

160K

C67

4.7uF

25V

C55

470pF

Q34

2N7002

2 3

R76

1206

2.74K

C69

VIN

R61

100

R63

C75

47pF

Q25

opt.

VERSION TABLE

R50

0.002

R41 R89

VSW

+Vout

R69

100V

1.0uF

C73

470pF

C66

1nF

200V

C24

1uF

C78

33nF

100V

1.0uF

1.91K 910

VIN

R55

100

Q26

opt.

R85

D28

MMBZ5236B

7.5V

R88

0-VOUT

R29

100K

1.0uF

100V

CMPSH1-4

Q14

Si7336ADP

678

0.039

124K

+Vin

C71

1uF

C77

2.2uF

opt.

PT-

DC1031A-A

R48 T1

VCC

C80

220uF

6.3V

opt.

R75

opt.

1.2

1/4W

-Vin

R22

15.0K

1.0uF

100V

C68

220uF

6.3V

0.022

PA0865(4:4:1:1)

-VOUT

C72

0.1uF

36-72Vin

R79

510

VERSION

opt.

Q32

opt.

R85

2.2nF

-VOUT

LTC3726EGN

ITH

FB/PH

GND

IS+

IS-

VCC

PT+

PT-

SLP

FS/SYNC

RUN/SS

MODE

PGND

R77

-VOUT

115

310

C76

opt.

R86

opt.

0.87uH

1.0uH

DC1031A-B

D25

C23

opt.

R53

opt.

0.039 2.2nF

C30

2.2nF

250V

C27

330pF

Q12

Si7336ADP

678

R83

C29

33nF

Q27

FCX491

DC1031A-C

536

opt

CMPSH1-4

R84

Q33

opt.

VCC

3.01K

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Item Qty Reference Part Description Manufacture / Part #

REQUIRED CIRCUIT COMPONENTS

1 4 C2,C3,C4,C5 CAP., X7R, 1.0uF, 100V, 20%, 1210 TDK, C3225X7R2A105M

2 2 C71,C24 CAP., X7R, 1uF, 16V 10%, 0805 TAIYO YUDEN, EMK212BJ105KG

3 2 C27,C70 CAP., X7R, 330pF, 25V, 10%, 0603 AVX, 06033C331KAT2A

4 2 C29,C78 CAP., X7R, 33nF, 25V, 10%, 0603 AVX, 06033C333KAT2A

5 1 C30 CAP., X7R, 2.2nF, 250V, 10%, 1812 MURATA, GA343QR7GD222KW01L

6 2 C31,C33 CAP., X5R, 100uF, 6.3V, 20%, 1210 TDK, C3225X5R0J107M

7 2 C73,C55 CAP., C0G, 470pF, 25V, 10%, 0603 AVX, 06033A471KAT2A

8 1 C66 CAP., C0G, 1nF, 200V, 10%, 1206 AVX, 12062A102KAT2A

9 1 C67 CAP., X7R, 4.7uF, 25V, 20%, 1206 TDK, C3216X7R1E475M

10 1 C68 CAP., POSCAP, 220uF, 6.3V, 20% 7343 SANYO, 6TPE220MI

11 1 C69 CAP., NPO, 1.5nF, 50V, 10%, 0805 AVX, 08055A152KAT2A

12 1 C72 CAP., X7R, 0.1uF, 25V, 10%, 0805 AVX, 08053C104KAT2A

13 1 C75 CAP., NPO, 47pF, 25V, 10%, 0603 AVX, 06033A470KAT2A

14 1 C77 CAP., X7R, 2.2uF, 16V, 20%, 1206 TDK, C3216X7R1C225M

15 1 C79 CAP., X7R, 2.2nF, 25V, 10%, 0603 AVX, 06033C222KAT2A

16 1 C81 CAP., C0G, 10pF, 50V, 5%, 0603 AVX, 06035A100JAT2A

17 1 D1 DIODE, Schottky, CMPSH1-4, 40V, SOT23 CENTRAL SEMI., CMPSH1-4-LTC

18 1 D28 Diode, MMBZ5236B, SOT23 DIODES INC., MMBZ5236B-7

19 1 D29 Diode, 1N4148W SOD-123 DIODES INC., 1N4148W-7-F

20 1 L1 INDUCTOR, 1.0uH VISHAY DALE, IHLP2525CZER1R0M01

0 L1 (second source) INDUCTOR, 1.0uH COOPER, HCP0703-1R0-R

21 1 L2 INDUCTOR, 0.87uH COOPER, HC1-R87

22 1 Q8 FET, N-CH,. Si7450DP, POWERPAK SO-8 VISHAY, Si7450DP

23 2 Q12,Q14 FET, N-CH,. Si7336ADP, POWERPAK SO-8 VISHAY, Si7336ADP

24 1 Q34 N-CH., Transistor. 2N7002 SOT23 DIODES INC., 2N7002-7-F

25 1 Q27 NPN TRANSISTOR, FCX491 ZETEX, FCX491

26 1 Q28 N-CH FET, 150V, FDC2512, Super SOT-6 FAIRCHILD, FDC2512

27 1 R2 RES., CHIP, 1.2, 1/4W, 5%, 1206 AAC, CR18-1R2JM

28 2 R54,R55 RES., CHIP, 100, 1/16W, 1%, 0603 VISHAY, CRCW06031000FRT6

29 1 R18 RES., CHIP, 365K, 1/8W, 1%, 0805 VISHAY, CRCW0805365KFKEB

30 1 R22 RES., CHIP, 15.0K, 1/16W, 1%, 0603 AAC, CR16-1502FM

31 1 R29 RES., CHIP, 100K, 1/8W, 5%, 0805 AAC, CR10-104JM

32 1 R41 RES., CHIP, 4.42K, 1/16W,1%, 0603 AAC, CR16-4421FM

33 1 R46 RES., CHIP, 604, 1/16W, 1%, 0603 AAC, CR16-6040FM

34 1 R48 RES., CHIP, 0.022, 1W, 2%, 2010 IRC, LRC-LRF2010-01-R022-G

35 1 R50 RES., CHIP, 0.002, 1W, 1%, 2512 PANASONIC, ERJM1WTF2M0U

36 1 R51 RES., CHIP, 2.4, 1/4W, 5%, 1206 AAC, CR18-2R4JM

37 1 R58 RES., CHIP, 5.1K, 1/16W, 5%, 0603 AAC, CR16-512JM

38 2 R3,R61 RES., CHIP, 100, 1/16W, 5%, 0603 AAC, CR16-101JM

39 2 R63,R66 RES., CHIP, 100K, 1/16W, 5%, 0603 AAC, CR16-104JM

40 1 R68 RES., CHIP, 6.2K, 1/16W, 5%, 0603 AAC, CR16-622JM

41 1 R69 RES., CHIP, 124K, 1/16W, 1%, 0603 AAC, CR16-1243FM

42 1 R76 RES., CHIP, 1K, 1/4W, 5%, 1206 AAC, CR18-102JM

43 1 R79 RES., CHIP, 510, 1/8W, 5%, 0805 e3 AAC, CR10-511JM

44 1 R85 RES., CHIP, 3.01K, 1/16W, 1%, 0603 AAC, CR16-3011FM

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