Linear Technology LT8608 User manual

dc2458af

DEMO MANUAL DC2458A

DESCRIPTION

LT8608

42V, 1.5V Micropower Synchronous

Step-Down Regulator

Demonstration circuit 2458A is a 42V, 1.5A micropower

synchronous step-down regulator featuring the LT

8608.

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

42V input. The wide input range allows a variety of input

sources, such as automotive batteries and industrial sup-

plies. The LT8608 is a compact, high efficiency, high speed

synchronous monolithic step-down switching regulator

that consumes only 2.5μA of quiescent current when

output is regulated at 5V. Top and bottom power switches,

compensation components and other necessary circuits

are inside of the LT8608 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

SKIPPINGpositioncanchangetheoperationmodetopulse-

skipping operation. Once JP1 is on SPREAD SPECTRUM

position, VCC is applied to the SYNC pin for low EMI spread

spectrum operation. To synchronous to an external clock, L, LT, LTC, LTM, Linear Technology, 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

move JP1 to SYNC and apply the external clock to the

SYNC turret. Figure 1 shows the efficiency of the circuit.

The demo board has an EMI filter installed. The radiated

EMI performances of the board (with EMI filter) are shown

in Figures 2 and 3. The red lines in Figures 2 and 3 are

CISPR25 class 5 peak limit. To use the EMI filter, the input

should be tied to VEMI, not VIN. An inductor L2, which is

a 0Ω jumper on the board by default now, can be added

in the EMI filter to further reduce the conducted emission.

The LT8608 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 DC2458A.

Design files for this circuit board are available at

http://www.linear.com/demo/DC2458A

Specifications are at TA= 25°C

SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS

VIN Input Voltage Range 5.5 42 V

VOUT Output Voltage 4.8 5 5.2 V

IOUT Maximum Output Current 1.5 A

fSW Switching Frequency 1.85 2 2.15 MHz

EFE Efficiency at DC VIN = 12V, IOUT = 0.75A 92.2 %

dc2458af

DEMO MANUAL DC2458A

QUICK START PROCEDURE

DC2458A is easy to set up to evaluate the performance

of the LT8608. Refer to Figure 4 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 5 for the proper scope

technique.

1. Setan inputpowersupply thatis capableof 42V/1.5A.

Then turn off the supply.

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

terminals VIN and GND.

3. Turn on the power at the input.

NOTE: Make sure that the input voltage never exceeds

42V.

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

the power at the input.

5. Once the proper output voltage is established, con-

nect a variable load capable of sinking 1.5A at 5V to

the output terminals VOUT and GND. Set the current

for 0A.

a. If efficiency measurements are desired, an am-

meter can be put in series with the output load in

order to measure the DC2458A’s output current.

b. A voltmeter can be placed across the output ter-

minals in order to get an accurate output voltage

measurement.

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 established again,

adjust the load and/or input within theoperatingrange

and observe the output voltage regulation, ripple

voltage, efficiency and other desired parameters.

8. An external clock can be added to the SYNC termi-

nal when SYNC function is used (JP1 on the SYNC

position). Please ensure that the chosen RTsets the

LT8608 switching frequency to equal or below the

lowest SYNC frequency. See the data sheet section,

Synchronization.

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

IOUT (A)

EFFICIENCY (%)

100

50 0.5

DC2458a F01

1.5

12V INPUT

24V INPUT

dc2458af

DEMO MANUAL DC2458A

QUICK START PROCEDURE

Figure 2. LT8608 Demo Circuit EMI Performance in CISPR25 Radiated Emission Test,

Antenna Polarization: Vertical (VIN = 14V, VOUT = 5V, IOUT = 1.5A, 2MHz Switching Frequency)

dc2458af

DEMO MANUAL DC2458A

Figure 3. LT8608 Demo Circuit EMI Performance in CISPR25 Radiated Emission Test,

Antenna Polarization: Horizontal (VIN = 14V, VOUT = 5V, IOUT = 1.5A, 2MHz Switching Frequency)

QUICK START PROCEDURE

dc2458af

DEMO MANUAL DC2458A

QUICK START PROCEDURE

Figure 4. Proper Measurement Equipment Setup

Figure 5. Measuring Output Ripple

dc2458af

DEMO MANUAL DC2458A

PARTS LIST

ITEM QTY REFERENCE PART DESCRIPTION MANUFACTURER/PART NUMBER

Required Circuit Components

1 1 C2 CAP, X7R, 4.7µF, 50V, 10% 1206 MURATA, GRM31CR71H475K

2 1 C4 CAP, X7R, 0.22µF, 16V, 10%, 0603 AVX, 0603YC224KAT2A

3 1 C5 CAP, C0G, 10pF, 25V, 5%, 0603 AVX, 06033A100JAT2A

4 1 C6 CAP, X7R, 47µF, 10V, 10%, 1210 MURATA, GRM32ER71A476KE20L

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

6 1 C8 CAP, X7R, 0.01µF, 16V, 10%, 0603 AVX, 0603YC103KAT2A

7 1 L1 IND, 2.2µH COILCRAFT, XFL4020-222MEC

8 1 R2 RES, CHIP, 18.2k, 1/10W, 1%, 0603 VISHAY, CRCW060318K2FKEA

9 1 R3 RES, CHIP, 49.9k, 1/10W, 1%, 0603 VISHAY, CRCW060349K9FKEA

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

11 1 R5 RES, CHIP, 187k, 1/10W, 1%, 0603 VISHAY, CRCW0603187KFKEA

12 1 U1 IC, REGULATOR, MSE10 LINEAR TECHNOLOGY, LT8608EMSE#PBF

Additional Demo Board Circuit Components

1 1 C1 CAP, ALUM 22µF 63V SUN ELECT, 63CE22BS

2 2 C3, C10 CAP, X7R, 4.7µF, 50V, 10% 1206 MURATA, GRM31CR71H475K

3 1 C9 CAP, X7R, 4.7µF, 16V, 10%, 0805 MURATA, GRM21BR71C475K73L

4 1 C11 CAP, X7R, 1µF, 50V, 10%, 0805 TDK, C2012X7R1H105K

5 2 C12, C13 CAP, X7R, 0.1µF, 50V, 10%, 0603 MURATA, GRM188R71H104KA93D

6 1 FB1 FERRITE BEAD 0805 TDK, MPZ2012S221AT000

7 1 L2 RES, CHIP, 0Ω, 3/4W, 2010 VISHAY, CRCW20100000Z0EF

8 0 R6 (OPT) RES, 0603

Hardware: For Demo Board Only

1 9 E1 TO E9 TESTPOINT, TURRET, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0

2 1 E10 (OPT) TESTPOINT, TURRET, 0.094"

3 1 JP1 DOUBLE ROW HEADER 2 × 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)

dc2458af

DEMO MANUAL DC2458A

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

C C

B B

A A

ALL CAPACITORS ARE 0603.

NOTES: UNLESS OTHERWISE SPECIFIED

1. ALL RESISTORS ARE 0603.

SUNCON

63CE22BS

(2MHz)

SYNC

SPREAD SPECTRUM

PULSE SKIPPING

BURST

VOUT

VCC

EN/UV

18.2k

SYNC

1.00M

22µF

63V

2.2µH

XFL4020-222MEC

GND

TR/SS

47µF

10V

1210

C11

1µF

50V

0805

0.01µF

C10

4.7µF

50V

1206

0.22µF

(Opt)

1µF

E8 PG

49.9k

JP1

1 2

VOUT

5V / 1.5A

GND

10pF

187k

1.00M

0 2010

C13

0.1µF

50V

4.7µF

50V

1206

VEMI

5.5V - 42V

FB1

MPZ2012S221AT000

4.7µF

50V

1206

C12

0.1µF

50V

LT8608EMSE

VIN

EN/UV

SYNC

VCC

TR/SS

FB 6

PG 8

SW 2

BST 1

GND

E10

VIN

5.5V - 42V

GND

4.7µF

16V

0805

dc2458af

DEMO MANUAL DC2458A

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

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

LT 0516 • 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.:

DC2458A

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