Datasheet LTC3725, LTC3726 Datasheet (Linear Technology)

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

DESCRIPTION

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

LTC3725 / LTC3726

Demonstration circuit 1031A-C is a 36V-72Vin, synchronous forward converter featuring the LTC3725/LTC3726. This circuit was designed specifically to attain a high current, low ripple, synchronously rectified forward to efficiently power 5.0V loads at up to 20A from a typical telecom input volt-

trol of the supply eliminating the need for an optocoupler, 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.

age range. This circuit features secondary-side con-

Table 1. Performance Summary (TA = 25°C)

PARAMETER CONDITION VALUE

Minimum Input Voltage 36V

Maximum Input Voltage 72V

Output Voltage V

Maximum Output Current 200LFM Airflow 20A

Typical Output Ripple V

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

Load Transient Response

VIN = 36V to 72V, I

OUT

VIN = 72V, I

OUT

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

Settling Time 40us

= 0A to 20A 5.0V

OUT

= 20A 100mV

OUT

P–P

Nominal Switching Frequency 300kHz

Efficiency VIN = 48V, I

= 20A 91.5% Typical

OUT

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 applied, 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 signals and bias power through T2.

The transition from primary to secondary control occurs 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-theshelf magnetics and attaining high efficiency.

For large values of input inductance, a 100V, 47uF electrolytic capacitor can be added across the input terminals to damp the input filter and provide adequate stability. See Linear Technology Application Note AN19 for a discussion on input filter stability analysis. A recommended part is the Sanyo 100MV39AX.

1

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 capacitor. See Figure 2 for proper scope probe technique.

1.

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.

2.

With power off, connect the supply to the input terminals +Vin and –Vin.

a.

Input voltages lower than 36V can keep the converter from turning on due to the undervoltage lockout feature of the LTC3725/LTC3726.

3.

Turn on the power at the input.

NOTE:

Make sure that the input voltage never ex-

ceeds 72V.

4.

Check for the proper output voltage of 5.0V

5.

Turn off the power at the input.

6.

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.

a.

If efficiency measurements are desired, an ammeter 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.

b.

A voltmeter with a capability of measuring at least 5.0V can be placed across the output terminals in order to get an accurate output voltage measurement.

b.

If efficiency measurements are desired, an ammeter capable of measuring 3.5Adc can be put in series with the input supply in order to measure the DC1031A-C’s input current.

c.

A voltmeter with a capability of measuring at least 72V can be placed across the input terminals in order to get an accurate input voltage measurement.

7.

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.

8.

Once the proper output voltage is established, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other desired parameters.

2

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

3

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

86

88

90

92

94

6 8 10 12 14 16 18 20

LOAD CURRENT (A)

EFFICIENCY (%)

36V

48V

72V

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 materials and layout.

Figure 3. Efficiency (200lfm airflow)

50mV/div

1us/div

Figure 4. Output Ripple Voltage (72Vin, 20Aout)

4

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Vout

200mV/DIV

Iout

10A/div

20us/DIV

Figure 5. Output Voltage Transient Response (48Vin, 10A to 20A step)

5

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)

6

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

Figure 9. Temp Data (36Vin, 20A, 25C, 200LFM airflow – back

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Figure 10. Temp Data (72Vin, 20A, 25C, 200LFM airflow – front)

Figure 11. Temp Data (72Vin, 20A, 25C, 200LFM airflow – back)

7

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

604

4.42K

+Vout

C68

6.3V

220uF

+

6.3V

2x100uF

L2

C31,C33

0.87uH

1/4W

R2

C67

1.2

-Vout

5.0V/20A

25V

4.7uF

VCC

Q27

FCX491

(SOT89)

1K

R76

D1

CMPSH1-4

Q12

VA

Si7336ADP

1/4W

D28

R85

3.01K

R55

100

R50

1W

R79

510

VSW

Si7336ADP

Q14

0.002 R54

100

VA

2.4

R51

115

T1

23.4 x 20.1 x 9.4mm PLANAR

VIN

72

10

C69

4

3 9

Si7450DP

Q8

1/4W

50V

1.5nF

1nF

C66

200V

0.022

R48

1W

R3

100

330pF

C27

R29

3x1.0uF

C3,C4,C5

100V

Q28

R41

4

MO DE

3

V CC

16

-VOUT

MMBZ5236B

7.5V

C70

R58

100K

S G

1

IS +

11

U2

330pF

IS -

10

S W

12

FG

2

PT+

15

C71

634

T2

1

C72

5.1K

C73

4

FB/IN+

IS

10

G AT E

7

ND RV

3

FB/PH

IT H

FS/S YNC

LT C372 6EGN

1uF

8

0.1uF

470pF

S LP

RU N/S S

P GND

G ND

PT-

14

PT-

5

100

R61

5

FS/IN-

U1

LT C372 5EM SE

UL VO

VCC

(SOT6)

FDC2512

8

SSFLT

2

1

R46

C77

2.2uF

C79

2.2nF

6.2K

R68

C75

5

9

7

6

13

8

R63

100K

G ND

11

P GND

6

V SLMT

9

C29

C24

1uF

47pF

124K

R69

100K

R66

C78

VIN

33nF

CONFI DENTIAL

LINEAR TECH NOLOGY CO RPORATION

PT-

D29

C81

33nF

VSW

-VOUT

C30

2.2nF

250V

CUSTOMER NOTICE

WI TH LTC PARTS.

THIS C IRCUI T IS DISTRIBUTED

TO C USTOMERS ON LY FOR USE

LINEA R TEC HNOLOG Y HA S MADE A BES T EF FO RT T O DES IGN A C IRCUIT

THA T ME ETS CUSTO MER-SUP PLIED S PECIF ICAT IONS; HO WEV ER, IT

536

R89

1N4148W

10pF

Q34

2N7002

TE CHNOLO GY A PPLICAT ION S ENGI NEERING FO R ASSIS TANCE .

AF FECT CIRCUIT PERF ORMA NCE OR RE LIABI LITY. CONTA CT LINE AR

SUB STIT UTIO N AND PRIN TED CIR UIT BO ARD LA YOUT MAY S IGNIF ICANT LY

RELIA BLE O PERAT ION IN THE A CTUAL APPLI CATIO N. COM PONEN T

REMA INS T HE CUST OME R'S RESPO NSIBIL ITY T O V ERIFY PROP ER AND

-VOUT

L1

1uH

C2

1.0uF

100V

+Vin

36-72Vin

-Vin

R18

365K

Figure 12. Simplified Schematic

C55

470pF

100uF, 6.3V CER TDK C3225X5R0J107M (1210)

1uF,100V TDK C3225X7R2A105M (1210)

C68 Sanyo 6TPE220MI

C30 Murata GA343QR7GD222KW01L (1812)

L1 Vishay IHLP-2525CZER1R0M-01

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

L2 Cooper HC1-R87

T1 PA0811 (4:4:2:1)

R22

15.0K

8

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

A

1

REV

+Vout

E3

C80

6.3V

220uF

+

C68

6.3V

220uF

+

E7

+VOUT

C31

100uF

C33

100uF

L2

0.87uH D25

*

R2

5

Q12

678

Si7336ADP

R79

510

Q14

Si7336ADP

T1

*

11531098

72

4

6 7 8

opt.

Q11

5

VIN

5

Q8

Si7450DP

C5

1.0uF

C4

1.0uF

C3

1.0uF

-Vout

E4

opt.

C23

R75

opt.

-

E8

6.3V

1.2

D1

*

VSW

5 678

100V

-VOUT

C67

4.7uF

25V

1/4W

VA

VCC

Q26

4

1

opt.

23

Q32

R50

1W

0.002

VA

VCC

4

1 23

VA

R52

*

50V

C69

R51

200V

C66

1nF

2 3

2 3 1

1

4

0

R3

R49

100

23

R76

1K

1206

opt.

1/4W

2.4

1/4W

1W

R48

*

C27

VCC

Q27

FCX491

1

R83

R55

100

1%

R54

100

1%

opt.

Q25

opt.

Q33

330pF

R41

*

4

MODE

3

16

-VOUT

D28

7.5V

0

MMBZ5236B

1

opt.

R56

11

*

R85

C70

330pF

10

12

2

0

R84

opt.

R53

T2

1

C72

5.1K

R58

4

IS

10

7

R29

100K

3

8

3

Q28

FDC2512

2 5 6

4 1

FB/PH

VCC

SG

IS+

IS-

SW

FG

PT+

PT-

15

14

PT-

1uF

C71

634

5

8

0.1uF

470pF

C73

R61

FB/IN+

GATE

U1

NDRV

LTC3725EMSE

UL VO

VCC

1

R46

604

C77

2.2uF

C76

opt.

R68

6.2K

ITH

5

R69

FS/SYNC

SLP

RUN/SS

PGND

GND

100

5

FS/IN-

GND

PGND

VSLMT

SSFL T

2

C24

C55

*

9

R66

100K

7

6

13

8

U2

LTC3726EGN

R63

*

VIN

11

6

R87

9

C29

33nF

1uF

470pF

PT-

Phone: (408)432-1900

Fax: (408)434-0507

Milpitas, CA 95035

D29

C81

VSW

C79

2.2nF

47pF

C75

C78

33nF

-VOUT

C30

2.2nF

250V

opt.

R86

0

R88

*

R89

1N4148W

1

10pF

Q34

2N7002

C69

2.2nF

PA0865(4:4:1:1)

PA0815(6:6:2:1)

910

opt

R85

0

R69

R63

160K

R48 T1

0.039

0.039 2.2nF

R41 R89

2.74K

1.91K 910

D25

CMPSH1-4

D1

opt.

Vout/Iout

3.3V/20A

2.5V/20A

1630 McCarthy Blvd.

2 3

1.5nF

TECHNOLOGY

-VOUT

TITLE

DATE

J. W U 12/5/05

APPROVALS

CONTRACT NO.

CHECKED

DRAWN

CUSTOMER NOTICE

536

3.01K

124K

100K5.0V/20A

0.022

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

opt.

CMPSH1-4

LINEAR TECHNOLOGY HAS MADE A BEST EFFORT TO DESIGN A

CIRCUIT THAT MEETS CUSTOMER-SUPPLIED SPECIFICATIONS;

HOWEVER, IT REMAINS THE CUSTOMER'S RESPONSIBILITY TO

VERIFY PROPER AND RELIABLE OPERATION IN THE ACTUAL

OF

1

SHEET

DC1031 A

DWG NO

FILENAME:

CAGE CODE

LTC3725EMSE, LTC3726EGN, 36V - 72Vin Forward Converter

SIZE

SCALE:

K. Mathews 12/5 /05

Wednesday , August 23, 2006

ENGINEER

DESIGNER

APPROVED

THIS CIRCUIT IS PROPRIETARY TO LINEAR TECHNOLOGY AND

SUPPLIED FOR USE WITH LINEAR TECHNOLOGY PARTS.

CIRUIT BOARD LAYOUT MAY SIGNIFICANTLY AFFECT CIRCUIT

TECHNOLOGY APPLICATIONS ENGINEERING FOR ASSISTANCE.

PERFORMANCE OR RELIABILITY. CONTACT LINEAR

APPLICATION. COMPONENT SUBSTITUTION AND PRINTED

L1

1.0uH

C2

1.0uF

100V

E1

+Vin

36-72Vin

E2

-Vin

R18

0

R77

365K

R22

15.0K

Figure 13. Full Board Schematic

VERSION TAB LE

*

VERSION

DC1031A-A

DC1031A-B

DC1031A-C

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

L2 Coil Tronics HC1-R87

L1 Vishay IHLP-2525CZER1R0M-01 or

C68 Sanyo 6TPE220MI

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

For All The Versions

COOPER HCP0703-1R0-R

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

9

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

Item Qty Reference Part Description Manufacture / Part #

REQUIRED CIRCUIT COMPONENTS1

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

10

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1031A-C

36V-72VIN, SYNCHRONOUS FORWARD CONVERTER

45 1 R89 RES., CHIP, 536, 1/16W, 5%, 0603 AAC, CR16-5360FM 46 1 T1 TRANSFORMER, 1750VDC BASIC, PA0811 PULSE, PA0811 47 1 T2 TRANSFORMER, 1500VRMS BASIC, PA0297 PULSE, PA0297 48 1 U1 I.C., LTC3725EMSE, MS10E LINEAR TECH., LTC3725EMSE 49 1 U2 I.C., LTC3726EGN, SSOP16GN LINEAR TECH., LTC3726EGN

ADDITIONAL DEMO BOARD CIRCUIT COMPONENTS2

1 0 C23,C76 (opt.) CAP., 0603

2 0 C80 (opt.) CAP., POSCAP, 220uF, 6.3V, 20% 7343

3 0 D25 (opt.) DIODE, Schottky, CMPSH1-4, 40V, SOT23

4 0 Q11 (opt.) FET, N-CH, POWERPAK SO-8

5 0 Q25,Q26 (opt.) NPN Transistor, FMMT619, SOT23

6 0 Q32,Q33 (opt.) PNP Transistor, FMMT718, SOT23

7 5 R49,R83,R84,R87,R88 RES., CHIP, 0, 1/16W, 0603 Panasonic, ERJ3GEY0R00V

8 0 R52 (opt.) RES., CHIP, 1206

9 0 R53,R56,R75 (opt.) RES., CHIP, 0603 11 1 R77 RES., CHIP, 0, 1/8W, 0805 AAC, CJ10-000M 12 0 R86 (opt.) RES., CHIP, 0805

HARDWARE-FOR DEMO BOARD ONLY:

1 2 E1,E2 TESTPOINT, TURRET, .094" MILL-MAX, 2501-2

2 2 E3,E4 STUD PEM, KFH-032-10

3 4 E3,E4

4 2 E3,E4 Ring, Lug Ring # 10 KEYSTONE 8205

5 2 E3,E4 WASHER, STAR #10 BRASS NICHEL ANY

6 2 E8,E7 TURRET, MILL-MAX2308-2-00-44

7 4 (STAND-OFF) STAND-OFF, NYLON 0.50" KEYSTONE 8833 (SNAP ON)

Notes:

1. Required Circuit Components are those parts that are required to implement the circuit function

2. Additional Demo Board Circuit Components are those parts that provide added functionality for the demo board but are not required in the actual circuit.

(2 EACH)

NUT, BRASS, #10-32 ANY

Figure 14. Bill of Materials

11