Linear Technology DC1736A Quick setup guide

dc1736af

DEMO MANUAL DC1736A

DESCRIPTION

LT3975

42V, 2.5A, 2.7µA Micropower

Buck Regulator

Demonstration circuit 1736A is a monolithic step-down

DC/DC switching regulator featuring the LT

3975. The

demo circuit is designed for 3.3V, 2.5A output from a 4.3V

to 42V input. The wide input range of the LT3975 allows

a variety of input sources, such as automotive batteries

and industrial supplies. The switching frequency can be

programmed either via oscillator resistor or external clock

up to 2MHz. When the circuit is synchronized to an external

clock connected to the SYNC terminal, the RTresistor (R5)

should be chosen to set the LT3975 internal switching

frequency at least 20% below the lowest synchroniza-

tion input frequency. Low ripple Burst Mode

operation

increases the efficiency at the light load while keeping the

output ripple below 15mV.

The circuit consumes only 2.7A of quiescent current.

The LT3975 internal boost diode and loop compensation

reduce the components count and solution size. The cur-

rent mode control scheme creates fast transient response

and good loop stability. The LT3975 is in shutdown when L, LT, LTC, LTM, µModule, 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.

PERFORMANCE SUMMARY

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 undervoltage lockout. Duringa short-circuit

fault, the LT3975 has current limit foldback to limit the

power dissipation.

The LT3975 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 1736A. The LT3975 is assembled in a

16-lead plastic MSOP package with an exposed pad for

low thermal resistance. Proper board layout is essential

for both proper operation and maximum thermal perfor-

mance. See the data sheet section PCB Layout and High

Temperature Considerations.

Design files for this circuit board are available at

http://www.linear.com/demo

TA= 25°C

PARAMETER CONDITIONS VALUE

Minimum Input Voltage 4.3V

Maximum Input Voltage 42V

Output Voltage, VOUT VIN = 4.3V ~ 42V 3.3V ± 3%

Switching Frequency RT= 78.7k 600kHz ±20%

Maximum Output Current, IOUT VIN = 4.3V ~ 42V 2.5A

Typical Efficiency VIN = 12V, IOUT = 2.5A 82.1%

Typical Output Voltage Ripple VIN = 12V, IOUT = 2.5A, 25MHz BW 20mV

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DEMO MANUAL DC1736A

QUICK START PROCEDURE

Demonstration circuit 1736A is easy to set up to evalu-

ate the performance of the LT3975. Refer to Figure 2 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 3 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.

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

5. Turn on the power at the input.

NOTE.Makesurethattheinputvoltagesdonotexceed42V.

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 voltages are 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.

LOAD CURRENT (A)

EFFICIENCY (%)

1.5 2.5

DC1735A F01

50 0.5 1 2

VOUT = 3.3V

VIN = 12V

fSW = 600kHz

Figure 1. Efficiency vs Load Current

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DEMO MANUAL DC1736A

QUICK START PROCEDURE

Figure 2. Proper Measurement Equipment Setup

Figure 3. Measuring Output Ripple

–

–+

VOUT LOAD

–

VIN

–

–+

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DEMO MANUAL DC1736A

PARTS LIST

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 1 C1 Cap., X5R, 47µF 10V 20% 1210 TDK, C3225X5R1A476M

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

3 1 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 D1 Diode, Scholtky, PowerDi5 DIODE INC, PDS360-13

7 1 L1 IND, 3.3µH VISHAY, IHLP2020CZER3R3M01

8 1 R1 Res., Chip, 1.00M 1/16W 1% 0402 VISHAY, CRCW04021M00FKED

9 1 R2 Res., Chip, 576k 1/16W 1% 0402 VISHAY, CRCW0402576KFKED

10 1 R5 Res., Chip, 78.7k 1/16W 1% 0402 VISHAY, CRCW040278K7FKED

11 1 R6 Res., Chip, 200k 1/16W 1% 0402 VISHAY, CRCW0402200KFKED

12 1 U1 I.C., MSE16 LINEAR TECH., LT3975EMSE

Additional Circuits

13 1 C4 Cap., Elect.,100µF 50V 10% SUN ELECT, 50CE100BS

14 1 C7 Cap., X5R, 1µF 16V 20% 0603 AVX, 0603YD105MAT

15 0 R7, R8 Res., 0402 OPT

Hardware—For Demo Board Only

16 7 E1, E2, E3, E4, E5, E6, E7 Turret, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0

17 2 JP1, JP2 JMP, 1X3-079 SAMTEC, TMM-103-02-L-S

18 2 Shunt Shunt, 2mm Ctrs. SAMTEC, 2SN-BK-G

dc1736af

DEMO MANUAL DC1736A

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

dc1736af

DEMO MANUAL DC1736A

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

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

LT 0712 • PRINTED IN USA

DEMONSTRATION BOARD IMPORTANT NOTICE

Linear Technology Corporation (LTC) 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 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

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 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

Mouser Electronics

Authorized Distributor

Click to View Pricing, Inventory, Delivery & Lifecycle Information:

Analog Devices Inc.:

DC1736A

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