Linear Technology LT8608 Manuale utente

DEMO MANUAL DC2521A

UG-1403 Rev. 0

DESCRIPTION

LT8608/LT8608B

42V, 1.5A Micropower

Synchronous Step-Down Regulator

Demonstration circuit 2521A is a 42V, 1.5A micropower

synchronous step-down regulator featuring the LT8608/

LT8608B. There are two assembly versions. DC2521A-A

is for the LT8608 and DC2521A-B is for the LT8608B.

The LT8608/LT8608B is a compact, high efficiency, high

speed synchronous monolithic step-down switching

regulator. Top and bottom power switches, compensa-

tion components and other necessary circuits are inside

of the 2mm × 2mm DFN package to minimize external

components and simplify design. The difference LT8608

and LT8608B is the LT8608 works under low ripple

Burst Mode

operation at light load condition, while the

LT8608B has pulse-skipping mode for light load. Due

to the Burst Mode operation, LT8608 consumes only

1.7μA of quiescent current when output is regulated at

5V. LT8608B has higher quiescent current because of its

pulse-skipping mode operation.

All registered trademarks and trademarks are the property of their respective owners.

PERFORMANCE SUMMARY

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

supplies.

The demo board has an EMI filter installed. The radiated

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

in Figure 2 and Figure 3. The red lines in Figure 2 and

Figure 3 are CISPR 25 Class 5 peak limit. To use the EMI

filter, the input should be tied to VEMI, not VIN. An induc-

tor 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 DC2521A.

Design files for this circuit board are available.

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 %

DEMO MANUAL DC2521A

UG-1403 Rev. 0

QUICK START PROCEDURE

DC2521A is easy to set up to evaluate the performance

of the LT8608/LT8608B. Refer to Figure 4 for proper

measurement equipment setup and follow the proce-

dure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. Set an input power supply that is capable of 42V/1.5A.

Then turn off the supply.

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

nals 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, connect

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

output terminals V

OUT

and GND. Set the current for0A.

a. If efficiency measurements are desired, an amme-

ter can be put in series with the output load in

order to measure the DC2521A’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 the operating range

and observe the output voltage regulation, ripple volt-

age, efficiency and other desired parameters.

Figure 2. LT8608/LT8608B Demo Circuit EMI Performance in

CISPR 25 Radiated Emission Test, Antenna Polarization: Vertical

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

LOAD CURRENT (A)

0.5

1.5

100

EFFICIENCY (%)

DC2521A F01

LT8608 (Burst Mode OPERATION)

LT8608B (PULSE-SKIPPING MODE)

Figure 1. Efficiency vs Load Current at 12V Input and 2MHz Switching Frequency

Figure 3. LT8608/LT8608B Demo Circuit EMI Performance in

CISPR25 Radiated Emission Test, Antenna Polarization:Horizontal

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

DEMO MANUAL DC2521A

UG-1403 Rev. 0

QUICK START PROCEDURE

Figure 4. Proper Measurement Equipment Setup

Figure 5. Measuring Output Ripple

OUT

GND

DEMO MANUAL DC2521A

UG-1403 Rev. 0

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, 1.0μF, 25V, 10%, 0603 MURATA, GRM188R71E105KA12D

6 1 L1 IND., 2.2µH WURTH ELEKTRONIK, 74438336022

7 1 R2 RES., CHIP, 18.2k, 1/10W, 1%, 0603 VISHAY, CRCW060318K2FKEA

8 1 R3 RES., CHIP, 49.9k, 1/10W, 1%, 0603 VISHAY, CRCW060349K9FKEA

9 2 R1, R4 RES., CHIP, 1MEG, 1/10W, 1%, 0603 VISHAY, CRCW06031M00FKEA

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

DC2521A-A Version Specific Components

1 1 U1 IC, REGULATOR, DFN-8 ANALOG DEVICES, LT8608EDC#PBF

DC2521A-B Version Specific Components

1 1 U1 IC, REGULATOR, DFN-8 ANALOG DEVICES, LT8608BEDC#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 C8 CAP., X7R, 1μF, 50V, 10%, 0805 TDK, C2012X7R1H105K

4 1 C9 CAP., X7R, 4.7μF, 16V, 10%, 0805 MURATA, GRM21BR71C475K73L

5 2 C11, C12 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 7 E1 − E7 TESTPOINT, TURRET, 0.094" MILL-MAX, 2501-2-00-80-00-00-07-0

2 1 E8 (OPT.) TESTPOINT, TURRET, 0.094"

3 4 MH1 − MH4 STAND-OFF, NYLON 0.50 TALL KEYSTONE, 8833 (SNAP ON)

DEMO MANUAL DC2521A

UG-1403 Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog

Devices for its use, nor for any infringements of patents or other rights of third parties that may result from its use. Specifications

subject to change without notice. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices.

SCHEMATIC DIAGRAM

C C

B B

A A

ALL CAPACITORS ARE 0603.

NOTES: UNLESS OTHERWISE SPECIFIED

1. ALL RESISTORS ARE 0603.

SUNCON

63CE22BS

(2MHz)

ASSEMBLY TYPE

VERSION

DC2521A-A

DC2521A-B

LT8608EDC

LT8608BEDC

VCC

C12

0.1µF

50V

(Opt)

10pF

187k

C10

4.7µF

50V

1206

47µF

10V

1210

1.00M

EN/UV

U1 *

VIN

VCC

FB 5

PG 6

SW 2

BST 1

GND

22µF

63V

C11

0.1µF

50V

1µF

4.7µF

50V

1206

GND

1µF

50V

0805

2.2µH

74438336022

VIN

5.5V - 42V

18.2k

FB1

MPZ2012S221AT000

GND

0.22µF

0 2010

E7 PG

VOUT

5V / 1.5A

49.9k

GND

4.7µF

50V

1206

VEMI

5.5V - 42V

4.7µF

16V

0805

VOUT

DEMO MANUAL DC2521A

UG-1403 Rev. 0

 ANALOG DEVICES, INC. 2018

UG17098-0-9/18(0)

www.analog.com

ESD Caution

ESD (electrostatic discharge) sensitive device. Charged devices and circuit boards can discharge without detection. Although this product features patented or proprietary protection

circuitry, damage may occur on devices subjected to high energy ESD. Therefore, proper ESD precautions should be taken to avoid performance degradation or loss of functionality.

Legal Terms and Conditions

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conditions set forth below (“Agreement”) unless you have purchased the Evaluation Board, in which case the Analog Devices Standard Terms and Conditions of Sale shall govern. Do not use the Evaluation

Board until you have read and agreed to the Agreement. Your use of the Evaluation Board shall signify your acceptance of the Agreement. This Agreement is made by and between you (“Customer”)

and Analog Devices, Inc. (“ADI”), with its principal place of business at One Technology Way, Norwood, MA 02062, USA. Subject to the terms and conditions of the Agreement, ADI hereby grants to

Customer a free, limited, personal, temporary, non-exclusive, non-sublicensable, non-transferable license to use the Evaluation Board FOR EVALUATION PURPOSES ONLY. Customer understands and

agrees that the Evaluation Board is provided for the sole and exclusive purpose referenced above, and agrees not to use the Evaluation Board for any other purpose. Furthermore, the license granted

is expressly made subject to the following additional limitations:Customer shall not (i) rent, lease, display, sell, transfer, assign, sublicense, or distribute the Evaluation Board;and (ii) permit any Third

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use of the Evaluation Board or termination of this Agreement, Customer agrees to promptly return the Evaluation Board to ADI. ADDITIONAL RESTRICTIONS. Customer may not disassemble, decompile

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