Linear Technology 2373A Quick setup guide

dc2373af

DEMO MANUAL DC2373A

Description

LT8641

65V, 3.5A Micropower Synchronous

Step-Down Silent Switcher

Demonstration circuit 2373A is a 65V, 3.5A micropower

synchronous step-down Silent Switcher

with spread

spectrum frequency modulation featuring the LT

8641.

The demo board is designed for 5V output from a 5.5V to

65V input. The wide input range allows a variety of input

sources, such as automotive batteries and industrial sup-

plies. The LT8641 is a compact, ultralow emission, high

efficiency, high speed synchronous monolithic step-down

switchingregulatorthat consumesonly 2.5μAof quiescent

current when output is regulated at 5V. Top and bottom

power switches, compensation components and other

necessary circuits are inside of the LT8641 to minimize

external components and simplify design.

The SYNC pin on the demo board is grounded by default

for low ripple burst mode operation. Move JP1 to PULSE

SKIPPING position can change the operation mode to

pulse-skipping operation. Once JP1 is on SPREAD SPEC-

TRUM position, VCC is applied to the SYNC pin for low

EMI spread spectrum operation. To synchronous to an

external clock, move JP1 to SYNC and apply the external

clock to the SYNC turret. Figure 1 shows the efficiency of

the circuit at 12V and 24V input in Burst Mode

operation

(input from VIN turret pin). Figure 2 shows the LT8641

L, LT, LTC, LTM, Linear Technology, Silent Switcher, Burst Mode and the Linear logo are

registered trademarks of Linear Technology Corporation. All other trademarks are the property

of their respective owners.

performance summary

temperature rising on DC2373A demo board under differ-

ent load conditions. The rated maximum load current is

3.5A, while derating is necessary for certain input voltage

and thermal conditions.

The demo board has an EMI filter installed. Under burst

and spread spectrum operation, the EMI performances of

the board (with EMI filter) are shown in Figure 3 and 4. The

red lines in Figure 3 and 4 are CISPR25 Class5 peak limit.

To achieve EMI/EMC performance as shown in Figure 3

and 4, the input EMI filter is required and the input voltage

should be applied at VEMI turret pin.

This board is suitable for a wide range of automotive,

telecom, industrial, and other applications.

The LT8641 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 DC2373A.

Design files for this circuit board are available at

http://www.linear.com/demo/DC2373A

Specifications are at TA= 25°C

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VIN Input Voltage Range 5.5 65 V

VOUT Output Voltage 4.8 5 5.2 V

IOUT Maximum Output Current Derating Is Necessary for Certain VIN and

Thermal Conditions

3.5 A

fSW Switching Frequency 1.85 2 2.15 MHz

EFF Efficiency VIN = 12V, IOUT = 1A 94 %

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DEMO MANUAL DC2373A

Quick start proceDure

DC2373A is easy to set up to evaluate the performance

of the LT8641. Refer to Figure 5 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. See Figure 6 for the proper scope

technique.

1. Set an input power supply that is capable of 65V/3.5A.

Then turn off the supply.

2. With power off, connect the supply tothe input terminals

VEMI and GND.

3. Turn on the power at the input.

NOTE: Make sure that the input voltage never exceeds 65V.

4. Check for the proper output voltage of 5V. Turn off the

power at the input.

5. Once the proper output voltage is established, connect a

variable load capable of sinking 3.5A at 5V to the output

terminals VOUT and GND. Set the current for 0A.

a. If efficiency measurements are desired, an ammeter

can be put in series with the output load in order to

measure the DC2373A’s output current.

b. A voltmeter can be placed across the output terminals

in order to get an accurate output voltage measure-

ment.

6. 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.

7. Once the proper output voltage is again established,

adjust the load and/or input within the operating range

and observe the output voltage regulation, ripple volt-

age, efficiency and other desired parameters.

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

when SYNC function is used (JP1 on the SYNC posi-

tion). Please ensure that the chosen RT sets the LT8641

switching frequency to equal or below the lowest SYNC

frequency. See the data sheet section, Synchronization.

dc2373af

DEMO MANUAL DC2373A

Quick start proceDure

Figure 1. Efficiency vs Load Current at 2MHz Switching Frequency

Figure 2. DC2373A Temperature Rising vs Load Current

IOUT (A)

EFFICIENCY (%)

100

50 21 3

DC2373a F01

3.5

1.50.5 2.5

12V INPUT

24V INPUT

LOAD CURRENT (A)

CASE TEMPERATURE RISE (°C)

021 3

DC2373a F02

3.5

1.50.5 2.5

VIN = 12V, fSW = 1MHz

VIN = 24V, fSW = 1MHz

VIN = 12V, fSW = 2MHz

VIN = 24V, fSW = 2MHz

dc2373af

DEMO MANUAL DC2373A

Figure 3. LT8641 Demo Circuit EMI Performance in CISPR25 Radiated Emission Test, Antenna Polarization:

Vertical (VIN = 14V, VOUT = 5V, IOUT = 3.5A, 2MHz Switching Frequency)

Figure 4. LT8641 Demo Circuit EMI Performance in CISPR25 Radiated Emission Test, Antenna Polarization:

Horizontal (VIN = 14V, VOUT = 5V, IOUT = 3.5A, 2MHz Switching Frequency)

Quick start proceDure

FREQUENCY (MHz)

AMPLITUDE (dBµV/m)

DC2373a F03

FREQUENCY (MHz)

AMPLITUDE (dBµV/m)

DC2373a F04

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DEMO MANUAL DC2373A

OUT

GND

Figure 5. Proper Measurement Equipment Setup

Figure 6. Measuring Output Ripple

Quick start proceDure

dc2373af

DEMO MANUAL DC2373A

parts List

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 2 C2, C12 CAP, X7R, 0.1µF, 100V, 10%, 0603 MURATA, GRM188R72A104KA35D

2 2 C4, C8 CAP, X7R, 0.1µF, 16V, 10%, 0603 MURATA, GRM188R71C104KA01D

3 1 C5 CAP, C0G, 10pF, 25V, 5%, 0603 AVX, 06033A100CAT2A

4 1 C6 CAP, X5R, 100µF, 10V, 20%, 1210 MURATA, GRM32ER61A107ME20L

5 1 C7 CAP, X7R, 1µF, 25V, 10%, 0603 MURATA, GRM188R71E105KA12D

6 1 C11 CAP, X7S, 4.7µF, 100V, 10%, 1206 AVX, 12061Z475KAT2A

7 1 L1 IND, 2.2µH VISHAY, IHLP2525CZER2R2M01

8 2 R1, R4 RES, CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA

9 1 R2 RES, CHIP, 18.2k, 1/10W, 1%, 0603 VISHAY, CRCW060318K2FKEA

10 1 R3 RES, CHIP, 100k, 1/10W, 1%, 0603 VISHAY, CRCW0603100KFKEA

11 1 R5 RES, CHIP, 191k, 1/10W, 1%, 0603 VISHAY, CRCW0603191KFKEA

12 1 R7 RES, CHIP, 0, 1/10W, 1%, 0604 VISHAY, CRCW06030000Z0EA

13 1 U1 IC, REGULATOR, 20-QFN, UDC LINEAR TECH,LT8641EUDC#PBF

Additional Demo Board Circuit Components

1 1 C1 CAP, ALUM 22µF, 100V SUN ELECT, 100CE22BS

2 2 C3, C10 CAP, X7S, 4.7µF, 100V, 10%, 1210 TDK, C3225X7S2A475K200AB

3 1 C9 CAP, X7R, 1µF, 25V, 10%, 0603 MURATA, GRM188R71E105KA12D

4 1 C13 CAP, X7R, 10µF, 10V, 10%, 0805 MURATA, GRM21BR71A106KE51L

5 1 C14 CAP, X7R, 0.1µF, 100V, 10%, 0603 MURATA, GRM188R72A104KA35D

6 1 FB1 FERRITE BEAD, 0805 TDK, MPZ2012S300A

7 1 L2 IND, 0.22µH VISHAY, IHLP1212BZERR22M11

8 0 R6 (OPT) RES, 0603

Hardware: For Demo Board Only

1 9 E2 TO E10 TESTPOINT, TURRET, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0

2 1 E1 (OPT) TESTPOINT, TURRET, 0.094"

3 1 JP1 DOUBLE ROW HEADER 2 x 4 0.079" SULLINS NRPN042PAEN-RC

4 1 XJP1 SHUNT, 0.079" CENTER SAMTEC 2SN-BK-G

5 4 MH1 TO MH4 STAND-OFF, NYLON 0.50" TALL KEYSTONE, 8833 (SNAP ON)

dc2373af

DEMO MANUAL DC2373A

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

dc2373af

DEMO MANUAL DC2373A

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

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

LT 0216 • 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 application

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.:

DC2373A

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