Linear Technology DC1848A User manual

dc1848af

DEMO MANUAL DC1848A

Description

LT3976

40V, 5A, 2MHz Step-Down Switching Regulator

with 3.3µA Quiescent Current

Demonstrationcircuit1848Ais amonolithicstep-downDC/

DC switching regulator featuring the LT3976. The LT3976

is a compact, high efficiency, high speed monolithic step-

down switching regulator that consumes only 3.3μA of

quiescent current. The demo circuit is designed for 3.3V,

5A output from a 4.3V to 40V input. The switching fre-

quency can be programmed either via oscillator resistor or

external clock up to 2MHz. To synchronize to an external

clock, move JP2 to SYNC and apply the external clock to

the SYNC turret. The RTresistor (R5) should be chosen

to set the LT3976 internal switching frequency at least

20% below the lowest synchronization input frequency.

Low ripple Burst Mode

operation increases the efficiency

at the light load while keeping the output ripple below

15mV. The SYNC pin on the demo board is grounded by

default for low ripple burst mode operation.

The LT3976 is in shutdown when the EN pin is low and

active when the pin is high. The threshold of the EN pin

is accurate at 1.02V with 60mV of hysteresis. Users can

populate R7 and R8 to provide a programmable under

voltage lockout. A low dropout voltage of 500mV is main-

tainedwhen the input voltagedropsbelow the programmed

performance summary

output voltage. During a short circuit fault, the LT3976

has current limit foldback to limit the power dissipation.

The demo board has an EMI filter installed. The EMI per-

formance of the demo board is shown on Figure 2. The

limit in Figure 2 is EN55022 Class B. The figure shows

the circuit passes the test with a wide margin. To use the

EMI filter, the input should be tied to VEMI, not VIN. VEMI

pad is on the back of the demo board.

The LT3976 data sheet gives a complete description of

the part, operation and application information. The data

sheet must be read in conjunction with this demo manual

for demo circuit 1848A. The LT3976 is assembled in a

16-lead plastic MSOP and 24-lead 5mm × 3mm QFN

packages with an exposed pad for low thermal resistance.

Proper board layout is essential for both proper operation

and maximum thermal performance. See the data sheet

sections for details.

Design files for this circuit board are available at

http://www.linear.com/demo

L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks

of Linear Technology Corporation. All other trademarks are the property of their respective

owners.

Specifications are at TA= 25°C

PARAMETER CONDITIONS VALUE

Minimum Input Voltage 4.3V

Maximum Input Voltage 40V

Output Voltage VOUT VIN = 4.3V ~ 40V 3.3V ± 3%

Switching Frequency RT= 130k 400kHz ± 20%

Guaranteed Maximum Output Current IOUT VIN = 4.3V ~ 40V 5A

Typical Efficiency VIN = 12V, IOUT = 5A 82.1%

Typical Output Voltage Ripple VIN = 12V, IOUT = 5A 20mV

dc1848af

DEMO MANUAL DC1848A

Quick start proceDure

Demonstration circuit 1848A is easy to set up to evalu-

ate the performance of the LT3976. Refer to Figure 3 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 input or output voltage

ripple by touching the probe tip directly across the VIN

or VOUT and GND terminals. See Figure 4 for the proper

scope technique.

1. Place JP1 on the ON position.

2. Place JP2 on the RT FREQ position.

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

and GND. Make sure that the input voltage does not

exceed 40V.

4. With power off, connect load from VOUT to GND.

5. Turn on the power at the input.

6. Check for the proper output voltage (3.3V).

NOTE: If there is no output, temporarily disconnect the

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

is shorted.

7. Once the proper output voltage is established, adjust

the load within the operating ranges and observe the

output voltage regulation, ripple voltage, efficiency and

other parameters.

8. An external clock can be added to the SYNC terminal

when SYNC function is used (JP2 on the SYNC posi-

tion). Please make sure that the SYNC frequency is at

least 20% higher than the set switching frequency. See

the data sheet section Synchronization.

performance summary

LOAD CURRENT (A)

EFFICIENCY (%)

80 20.5

DC1848A F01

51.5 4.53 3.52.5 41

VIN = 12V

VOUT = 3.3V

fS= 400kHz

Figure 1. LT3976 Efficiency vs Load Current Figure 2. LT3976 Demo Board EMI Performance,

Switching Frequency 400kHz

dc1848af

DEMO MANUAL DC1848A

Quick start proceDure

Figure 3. Proper Measurement Equipment Setup

Figure 4. Measuring Input or Output Ripple

dc1848af

DEMO MANUAL DC1848A

parts List

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Demo Board Circuit Components

1 2 C1, C8 Cap., X5R, 47µF, 10V, 20% 1210 TDK, C325X5R1A476MT

2 1 C2 Cap., X5R, 0.47µF, 25V, 10% 0603 TDK, C1608X5R1E474K

3 2 C3 Cap., X5R, 10µF, 50V, 10%,1210 TDK, C3225X5R1H106K

4 1 C5 Cap., C0G, 10pF, 50V, 10% 0402 TDK, C1005C0G1H100D

5 1 C6 Cap., X7R, 10nF, 25V, 10%, 0402 TDK, C1005X7R1E103K

6 1 C7 Cap., C0G, 470pF, 50V, 10%, 0402 AVX, 04025A471KAT2A

7 1 D1 DIODE, Schottky, PowerDi5 DIODE INC., PDS540-13

8 1 L1 IND., 3.3µH VISHAY, IHLP2525CZER3R3M01

9 1 R1 Res., Chip, 1.00M, 1/16W, 1% 0402 NIC, NRC04F1004TRF

10 1 R2 Res., Chip, 576K, 1/16W, 1% 0402 VISHAY, CRCW0402576KFKED

11 1 R3 Res., Chip, 2, 1/16W, 1% 0402 VISHAY, CRCW04022R00FKED

12 1 R5 Res., Chip, 130k, 1/16W, 1% 0402 VISHAY, CRCW0402130KFKED

13 1 R6 Res., Chip, 200k, 1/16W, 1% 0402 VISHAY,CRCW0402200KFKED

14 1 U1 I.C., MSE16 LINEAR TECH., LT3976EMSE

Additional Demo Board Circuit Components

15 1 C11 Cap., X5R, 1µF 16V 20%, 0603 AVX, 0603YD105MAT

16 1 C4 Cap., Elect.,100µF, 50V, 10% SUN ELECT, 50CE100BS

17 1 C9 Cap., X5R, 10µF, 50V, 10%,1210 TDK, C3225X5R1H106K

18 1 C10 Cap., Alum. Electro., 33µF, 50V SUNCON, 50HVP33M

19 1 L2 Ind., 1.0µH XAL4020 COILCRAFT, XAL4020-102MEC

20 1 L3 Ind., 3.3µH XAL5030 COILCRAFT, XAL5030-332MEC

21 0 R7, R8 Res., 0402 OPT

Hardware/Components (for Demo Board Only)

22 7 E1, E2, E3, E4, E5, E6, E7 Turret, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0

23 2 JP1, JP2 JMP, 1X3-079 SAMTEC, TMM-103-02-L-S

24 2 XJP1, XJP2 SAMTEC, 2SN-BK-G

dc1848af

DEMO MANUAL DC1848A

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.

schematic Diagram

D D

C C

B B

A A

ALL CAPACITORS ARE 0402.

NOTES: UNLESS OTHERWISE SPECIFIED

1. ALL RESISTORS ARE 0402.

SUNCON

50CE100BS

VIN

VOUT

VIN

PDS540

2 1

E7 SYNC

10nF

GND

EN E5

VEMIVEMI

10uF

50V

1210

10uF

50V

1210

10pF

470pF

OPT

0603

OPT

0603

OPT

0603

OPT

0603

10uF

50V

1210

10uF

50V

1210

3.3uH

IHLP2525CZER3R3M01

3.3uH

IHLP2525CZER3R3M01

1.0uH

XAL4020-102ME

1.0uH

XAL4020-102ME

JP1

OFF

JP1

OFF

576k

LT3976EMSE

OUT 3

FB 1

VIN

BOOST 4

SW 5

SYNC 16

GND

VIN

11 VIN

SW 6

SW 7

RT 14

3.3uH

XAL5030-332ME

3.3uH

XAL5030-332ME

C11

1uF

0603

16V

C11

1uF

0603

16V

130K

(400kHz)

130K

(400kHz)

47uF

10V

1210

47uF

10V

1210

100uF

50V

100uF

50V

1.00M

E2 GND

200K

0.47uF

0603

0.47uF

0603

VOUT

3.3V / 5A

VOUT

3.3V / 5A

JP2

SYNC

RT FREQ

JP2

SYNC

RT FREQ

VIN

4.3V - 40V E3

VIN

4.3V - 40V

C10

33uF

50V

50HVP33

C10

33uF

50V

50HVP33

47uF

10V

1210

47uF

10V

1210

dc1848af

DEMO MANUAL DC1848A

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 1012 • 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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