Analog Devices EVAL-LT8641A-AZ Guida rapida alla configurazione

EVAL-LT8641A-AZ Demo Manual

65V, 3.5A/5A Peak Synchronous

Step-Down Silent Switcher

General Description

Evaluation circuit EVAL-LT8641A-AZ is a 65V, 3.5A/5A

peak synchronous step-down Silent Switcher®with

spread spectrum frequency modulation featuring the

LT®8641A. 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 supplies. The LT8641A is a compact, ultralow

emission, high efficiency, high speed synchronous

monolithic step-down switching regulator. Top and

bottom power switches, compensation components, and

other necessary circuits inside the LT8641A minimize

external components and simplify design. The special

Silent Switcher architecture minimizes EMI emissions.

The selectable spread spectrum mode can further

improve EMI performance. Ultralow 2.5μA quiescent

current in Burst Mode®operation achieves high efficiency

at very light loads. Fast minimum on-time of 35ns enables

high VIN to low VOUT conversion at high frequency.

The LT8641A switching frequency can be programmed

either through oscillator resistor or external clock over a

200kHz to 3MHz range. The default frequency of the

evaluation board is 2MHz. The SYNC pin on the

evaluation board is grounded by JP1 for low ripple burst

mode operation. Move JP1 to PULSE SKIPPING position

to change the operation mode to pulse-skipping

operation. Once JP1 is on SPREAD SPECTRUM

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

spread spectrum operation. To synchronize 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.

Figure 2 shows EMI performances of the board (with EMI

filter). The red lines in Figure 2 are CISPR25 Class5 peak

limit. The figure shows that the circuit passes the test with

a wide margin. To achieve EMI/EMC performance, as

shown in Figure 2, the input EMI filter is required, and the

input voltage should be applied at the VEMI turret.

The LT8641A data sheet gives a complete description of

the part, operation, and application information. Read the

data sheet in conjunction with this user guide for EVAL-

LT8641A-AZ. The LT8641A is assembled in a 3mm × 4mm

plastic QFN package with exposed pad for low thermal

resistance. The layout recommendations for low EMI

operation and maximum thermal performance are

available in the “Low EMI PCB Layout and Thermal

Considerations” and “Peak Output Current” sections of the

data sheet.

Performance Summary Specifications are at TA= 25°C

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

VIN

Input Voltage Range

5.50

65.00

VOUT

Default Output Voltage

VIN = 12V, IOUT = 0A to 3.5A

4.80

5.00

5.20

IOUT

Maximum Continuous

Output Current

VIN = 12V

3.50

fsw

Switching Frequency

1.85

2.00

2.15

MHz

Eff

Efficiency

VIN = 12V, fSW = 2MHz,

VOUT = 5V, IOUT = 1A

EVAL-LT8641A-AZ Demo Manual

65V, 3.5A/5A Peak Synchronous

Step-Down Silent Switcher

www.analog.com

Analog Devices | 2

Typical Performance Characteristics

Figure 1. LT8641A Eval Circuit Efficiency vs. Load Current

(2MHz Switching Frequency, Burst Mode)

EVAL-LT8641A-AZ Demo Manual

65V, 3.5A/5A Peak Synchronous

Step-Down Silent Switcher

www.analog.com

Analog Devices | 3

Figure 2. LT8641A Eval Circuit Conducted and Radiated EMI Performance in CISPR25 Emission Test

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

65V, 3.5A/5A Peak Synchronous

Step-Down Silent Switcher

www.analog.com

Analog Devices | 4

EVAL-LT8641A-AZ Demo Manual

Quick Start Procedure

The evaluation board EVAL-LT8641A-AZ is easy to set

up to evaluate the performance of the LT8641A. See

Figure 3 for proper measurement equipment setup

and follow this procedure.

1. Set an input power supply capable of 65V/5A.

2. With power off, connect the input power supply

to VEMI and GND.

3. With power off, connect the loads from VOUT to

GND.

4. Place the voltmeters across the output voltage

sense terminals VOUT_SENSE and GND to get

accurate output voltage measurements.

5. Turn on the power at the input.

Note: Make sure that the input voltage does not exceed

65V.

6. Check for proper output voltages. Regulate the

output at 5.0V (±4%).

Note: If there is no output, temporarily disconnect the load

to make sure the load is not set too high.

7. 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.

Note: When measuring the input or output voltage ripple,

take care to avoid a long ground lead on the oscilloscope

probe. Measure the output voltage ripple by touching the

probe tip directly across the output capacitor. See

Figure 4 for the proper scope technique.

8. An external clock can be added to the SYNC

terminal when SYNC function is used (JP1 on

the SYNC position). Ensure the chosen RT sets

the LT8641A switching frequency to equal or

below the lowest SYNC frequency. Refer to the

data sheet section “Synchronization and Spread

Spectrum”.

EVAL-LT8641A-AZ Demo Manual

65V, 3.5A/5A Peak Synchronous

Step-Down Silent Switcher

www.analog.com

Analog Devices | 5

Figure 3. Proper Measurement Equipment Setup

Figure 4. Scope Probe Placement for Measuring Input or Output Voltage Ripple

EVAL-LT8641A-AZ Demo Manual

65V, 3.5A/5A Peak Synchronous

Step-Down Silent Switcher

www.analog.com

Analog Devices | 6

Bill of Materials

ITEM

QTY

REFERENCE

PART DESCRIPTION

MANUFACTURER/PART NUMBER

Required Evaluation Kit Components

C2, C12

CAP., X7R, 0.1µF, 100V, 10%, 0603

MURATA, GRM188R72A104KA35D

C4, C8

CAP., X7R, 0.1µF, 16V, 10%, 0603

MURATA, GRM188R71C104KA01D

CAP., C0G, 10pF, 25V, 5%, 0603

AVX, 06033A100CAT2A

CAP., X5R, 100µF, 10V, 20%, 1210

MURATA, GRM32ER61A107ME20L

CAP., X7R, 1.0µF, 25V, 10%, 0603

MURATA, GRM188R71E105KA12D

C11

CAP., X7R, 4.7µF, 100V, 10% 1206

MURATA, GRM31CZ72A475ME11L

IND., 2.2µH

COILCRAFT, XGL6030-222MEC

R1, R4

RES., CHIP, 1MEG, 1/10W, 1%, 0603

VISHAY, CRCW06031M00FKEA

RES., CHIP, 18.2K, 1/10W, 1%, 0603

VISHAY, CRCW060318K2FKEA

RES., CHIP, 100K, 1/10W, 1%, 0603

VISHAY, CRCW0603100KFKEA

RES., CHIP, 191K, 1/10W, 1%, 0603

VISHAY, CRCW0603191KFKEA

IC, REGULATOR, 20-QFN, UDC

ANALOG DEVICES,

LT8641ARUDCM#WPBF

Additional Evaluation Kit Components

CAP., ALUM 22µF 100V

SUN ELECT, 100CE22BS

C3, C10

CAP., X7S, 4.7µF, 100V, 10%, 1210

TDK, CGA6M3X7S2A475K200AB

CAP., X7R, 1.0µF, 25V, 10%, 0603

MURATA, GRM188R71E105KA12D

C13

CAP., X7R, 10µF, 10V, 10%, 0805

MURATA, GRM21BR71A106KE51L

C14

CAP., X7R, 0.1µF, 100V, 10%, 0603

MURATA, GRM188R72A104KA35D

FB1

FERRITE BEAD 1206

WURTH, 78279221281

L2 (OPT.)

IND.,

R6 (OPT.)

RES., 0603

RES., CHIP, 0, 1/10W, 1%, 0604

VISHAY, CRCW06030000Z0EA

R10

RES., CHIP, 10K, 1/10W, 1%, 0603

VISHAY, CRCW060310K0FKEA

R11

RES., CHIP, 0.1Ω, 3W,1%,2512

SUSUMU, KRL3264E-C-R100-F-T1

R12

RES., CHIP, 50Ω, 1/10W, 1%, 0603

CRCW060350R0FKEA

MOSFET, N-CH,40V,14A, DPAK

VISHAY, SUD50N04-8M8P-4GE3

Hardware for Evaluation Kit Only

E2 to E10,

E12,

E15 to E17

TESTPOINT, TURRET, .094"

MILL-MAX, 2501-2-00-80-00-00-07-0

E1 (OPT.)

TESTPOINT, TURRET, .094"

JP1

DOUBLE ROW HEADER 2 x 4 .079"

SULLINS NRPN042PAEN-RC

XJP1

SHUNT, .079" CENTER

SAMTEC 2SN-BK-G

MH1-MH4

STAND-OFF, NYLON 0.50" TALL

KEYSTONE, 8833 (SNAP ON)

EVAL-LT8641A-AZ Demo Manual

65V, 3.5A/5A Peak Synchronous

Step-Down Silent Switcher

www.analog.com

Analog Devices | 7

Schematic Diagram

EVAL-LT8641A-AZ Demo Manual

65V, 3.5A/5A Peak Synchronous

Step-Down Silent Switcher

Revision History

REVISION

NUMBER

REVISION

DATE

DESCRIPTION

PAGES

CHANGED

05/23

Initial release

—

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. Trademarks and registered trademarks are the

property of their respective owners.

w w w . a n a l o g . c o m

Analog Devices | 8

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