Analog Devices DC2468A Quick setup guide

dc2468af

DEMO MANUAL DC2468A

DESCRIPTION

LT8645S

65V, 8A Micropower Synchronous

Step-Down Silent Switcher 2

Demonstration circuit 2468A is a 65V, 8A micropower syn-

chronous step-down second generation Silent Switcher

with spread spectrum frequency modulation featuring the

LT8645S. The demo board is designed for 5V output from

a 5.6V to 65V input. The wide input range allows a variety

of input sources, such as automotive batteries and indus-

trial supplies. The LT8645S is a compact, ultralow emis-

sion, high efficiency, and high speed synchronous mono-

lithic step-down switching regulator. The integrated bypass

capacitors optimize all the fast current loops and make it

easier to minimize EMI/EMC emissions by reducing layout

sensitivity. Selectable spread spectrum mode can further

improve EMI/EMC performance. Ultralow quiescent cur-

rent in Burst Mode

operation achieves high efficiency at

very light loads. Fast minimum on-time of 40ns enables

high VIN to low VOUT conversion at high frequency.

The LT8645S switching frequency can be programmed

either via oscillator resistor or external clock over a

200kHz to 2.2MHz range. The default frequency of demo

circuit 2468A is 2MHz. The SYNC pin on the demo board

is grounded (JP1 at BURST position) by default for low

ripple Burst Mode operation. To synchronize to an external

clock, move JP1 to SYNC and apply the external clock

to the SYNC terminal. Spread spectrum mode and pulse

skipping mode can be selected respectively by moving

JP1 shunt. Figure 1 shows the efficiency of the circuit at

12V input and 24V input in Burst Mode operation (input

from VIN terminal to bypass the EMI filter). Figure 2 shows

the LT8645S temperature rising on DC2468A demo board

under different load conditions. The rated maximum load

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

registered trademarks of Analog Devices, Inc. All other trademarks are the property of their

respective owners.

current is 8A, while derating is necessary for certain input

voltage and thermal conditions. Low switching frequency

can extend the output load capability by reducing the

power dissipations. Figure 3 shows the temperature ris-

ing at 500kHz switching frequency.

The demo board has an EMI filter installed. The EMI

performance of the board (with EMI filter) is shown on

Figure 4. The red line in Radiated EMI Performance is

CISPR25 Class 5 peak limit. The figure shows that the

circuit passes the test with a wide margin. To achieve EMI/

EMC performance as shown in Figure 4, the input EMI

filter is required and the input voltage should be applied

at VEMI terminal. An inductor can be added in the EMI

filter to further reduce the conducted emission. The EMI

filter can be bypassed by applying the input voltage at

VIN terminal.

The LT8645S 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 2468A. The LT8645S is assembled in a

6mm × 4mm LQFN package with exposed pads for low

thermal resistance. The layout recommendations for low

EMI operation and maximum thermal performance are

available in the data sheet section Low EMI PCB Layout

and Thermal Considerations.

Design files for this circuit board are available at

http://www.linear.com/demo/DC2468A

PERFORMANCE SUMMARY

Specifications are at TA= 25°C

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VIN_EMI Input Supply Range with EMI Filter 5.6 65 V

VOUT Output Voltage 4.85 5 5.15 V

IOUT Maximum Output Current Derating is Necessary for Certain VIN and Thermal Conditions 8 A

fSW Switching Frequency 1.85 2 2.15 MHz

EFF Efficiency VIN = 12V, IOUT = 4A 93.8 %

dc2468af

DEMO MANUAL DC2468A

DESCRIPTION

Figure 1. LT8645S Demo Circuit DC2468A Efficiency vs

Load Current (Input from VIN Terminal)

Figure 3. LT8645S Demo Circuit DC2468A

Temperature Rising vs Input Voltage (500kHz)

Figure 2. LT8645S Demo Circuit DC2468A

Temperature Rising vs Input Voltage (2MHz)

OUT

= 5V

POWER LOSS

= 2MHz

SYNC/MODE = GND

EFFICIENCY

= 12V

= 24V

LOAD CURRENT (A)

100

0.8

1.6

2.4

3.2

4.0

4.8

5.6

6.4

EFFICIENCY (%)

POWER LOSS (W)

dc2468a F01

OUT

= 5V

= 500kHz

OUT

= 8A

OUT

= 6A

OUT

= 4A

INPUT VOLTAGE (V)

100

TEMPERATURE RISING (°C)

dc2468a F03

OUT

= 5V

= 2MHz

OUT

= 8A

OUT

= 6A

OUT

= 4A

INPUT VOLTAGE (V)

100

TEMPERATURE RISING (°C)

dc2468a F02

dc2468af

DEMO MANUAL DC2468A

DC2468A DEMO BOARD

(WITH EMI FILTER INSTALLED)

14V INPUT TO 5V OUTPUT AT 4A, f

= 2MHz

FIXED FREQUENCY MODE

SPREAD SPECTRUM MODE

FREQUENCY (MHz)

–40

–30

–20

–10

AMPLITUDE (dBµV/m)

dc2468 F04a

Conducted EMI Performance

Radiated EMI Performance

(CISPR25 Radiated Emission Test with Class 5 Peak Limits)

VERTICAL POLARIZATION

PEAK DETECTOR

CLASS 5 PEAK LIMIT

SPREAD SPECTRUM MODE

FIXED FREQUENCY MODE

FREQUENCY (MHz)

100

200

300

400

500

600

700

800

900

1000

–5

AMPLITUDE (dBµV/m)

dc2468 F04b

DC2468A DEMO BOARD

(WITH EMI FILTER INSTALLED)

14V INPUT TO 5V OUTPUT AT 4A, f

= 2MHz

HORIZONTAL POLARIZATION

PEAK DETECTOR

CLASS 5 PEAK LIMIT

SPREAD SPECTRUM MODE

FIXED FREQUENCY MODE

FREQUENCY (MHz)

100

200

300

400

500

600

700

800

900

1000

–5

AMPLITUDE (dBµV/m)

dc2468 F04c

Figure 4. LT8645S Demo Circuit DC2468A EMI Performance (14V Input from VEMI, with EMI Filter, IOUT = 4A)

DESCRIPTION

dc2468af

DEMO MANUAL DC2468A

IN_EMI

QUICK START PROCEDURE

Demonstration circuit 2468A is easy to set up to evalu-

ate the performance of the LT8645S. 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. Measure the output voltage ripple by

touching the probe tip directly across the output capaci-

tor. See Figure 6 for the proper scope technique. Figure 7

shows the output voltage ripple measured at the output

capacitor C9.

1. Place JP1 on BURST position.

2. With power off, connect the input power supply to

VEMI and GND. If the input EMI filter is not desired,

connect the input power supply to VIN and GND.

3. With power off, connect the load from VOUT to GND.

4. Turn on the power at the input.

NOTE:Make sure that the input voltage does not

exceed 65V.

5. Check for the proper output voltage (VOUT = 5V).

NOTE:If there is no output, temporarily disconnect the

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

is shorted.

6. 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.

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

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

tion). Please make sure that R2 should be chose to set

the LT8645S switching frequency equal to or below the

lowest SYNC frequency. JP1 can also set LT8645S in

spread spectrum mode (JP1 on the SPREAD-SPEC-

TRUM position) or pulse skipping mode (JP1 on the

PULSE-SKIPPING position).

Figure 5. Proper Measurement Equipment Setup

dc2468af

DEMO MANUAL DC2468A

QUICK START PROCEDURE

Figure 6. Measuring Output Ripple at Output Capacitor C9

Figure 7. LT8645S Demo Circuit DC2468A Output Voltage Ripple

(12V Input, IOUT = 8A, Full BW)

VOUT

GND

500ns/DIV

VOUT

5mV/DIV

AC-COUPLED

dc2468a F07

dc2468af

DEMO MANUAL DC2468A

PARTS LIST

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 2 C2, C12 CAP., X7R, 0.47μF, 100V, 10%, 0805 MURATA, GRM21BR72A474KA73L

2 1 C6 CAP., X5R, 100μF, 10V, 20%, 1210 MURATA, GRM32ER61A107ME20L

3 1 C8 CAP., X7R, 0.1μF, 25V, 10%, 0603 MURATA, GRM188R71E104KA01D

4 1 C9 CAP., X5R, 10μF, 25V, 20%, 0603 MURATA, GRM188R61E106MA73D

5 1 C16 CAP., C0G, 4.7pF, 50V, ±0.25pF, 0603 MURATA, GRM1885C1H4R7CA01D

6 1 C17 CAP., X7S, 4.7μF, 100V, 10%, 1210 MURATA, GRJ32DC72A475KE11L

7 1 C20 CAP., X7R, 1μF, 16V, 10%, 0603 MURATA, GRM188R71C105KA12D

8 1 L1 INDUCTOR, 1.0μH, XEL6030 COILCRAFT, XEL6030-102MEC

9 2 R1, R5 RES., CHIP, 100k, 1/10W, 1%, 0603 VISHAY, CRCW0603100KFKEA

10 1 R2 RES., CHIP, 17.8k, 1/10W, 1%, 0603 VISHAY, CRCW060317K8FKEA

11 1 R3 RES., CHIP, 243k, 1/10W, 1%, 0603 VISHAY, CRCW0603243KFKEA

12 1 R7 RES., CHIP, 1M, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA

13 1 U1 I.C., STEP-DOWN SWITCHER, 6mmX4mm LQFN LINEAR TECH., LT8645SEV#PBF

Additional Demo Board Circuit Components

1 1 C1 CAP., ALUM 22μF, 100V, 10% SUNCON, 100CE22BS

2 2 C3, C10 CAP., X7R, 2.2μF, 100V, 10%, 1210 MURATA, GRM32ER72A225KA35L

3 1 C4 CAP., X7R, 0.1μF, 100V, 10%, 0603 MURATA, GRM188R72A104KA35D

4 1 C14 CAP., X5R, 0.1μF, 100V, 10%, 0402 MURATA, GRM155R62A104KE14D

5 0 C18 (OPT) CAP., 0603

6 0 C19 (OPT) CAP., 1210

7 1 FB1 FERRITE BEAD 100Ω 8A SMD 1812 WURTH ELEKTRONIK, 74279226101

8 0 R6 (OPT) RES., OPTION, 0603

9 1 R8 RES., CHIP, 0Ω, 1/10W, 1%, 0603 VISHAY, CRCW06030000Z0EA

Hardware: For Demo Board Only

1 8 E1, E5-E9, E11, E14 TESTPOINT, TURRET, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0

2 4 E2, E10, E12, E13 TESTPOINT, TURRET, 0.061" MILL-MAX, 2308-2-00-80-00-00-07-0

3 1 JP1 2X4, 0.079" DOUBLE ROW HEADER WURTH ELEKTRONIK, 62000821121

4 1 XJP1 SHUNT, 0.079" CENTER WURTH ELEKTRONIK, 60800213421

5 4 J1-J4 JACK BANANA KEYSTONE, 575-4

6 4 MH1-MH4 STAND-OFF, NYLON 0.50" TALL WURTH ELEKTRONIK, 702935000

dc2468af

DEMO MANUAL DC2468A

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 0603.

NOTES: UNLESS OTHERWISE SPECIFIED

1. ALL RESISTORS ARE 0603.

100CE22BS

SYNC

BURST

SPREAD-SPECTRUM

PULSE-SKIPPING

SEE DEMO MANUAL

17.8K

GND

FB1

74279226101 E11

0.47uF

100V

0805

GND

OPT

C17

4.7uF

100V

1210

C14

0.1uF

0402

100V

JP1

1 2

SYNC

E8 PG

C12

0.47uF

100V

0805

100uF

10V

1210

22uF

100V

243K

0.1uF

100V

2.2uF

1210

100V

VOUT

5V / 8A

TR/SS

VIN

5.6V - 65V

J4 GND

C16

4.7pF

C18

OPT

C20

1uF

16V

1.0uH

XEL6030-102

10uF

25V

0.1uF

E10

VEMI

C10

2.2uF

1210

100V

E6 CLKOUT

100K

E12

LT8645S

VIN

SYNC

VCC

BIAS

BST

GND1

GND2

TR/SS

GND1

GND2

VIN

GND2

GND

CLKOUT

GND

C19

OPT

1210

E14 BIAS

E13

100K

VIN

dc2468af

DEMO MANUAL DC2468A

 LINEAR TECHNOLOGY CORPORATION 2017

LT 0517 • 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.:

DC2468A

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