Analog Devices EVAL-LT8641A-AZ Quick setup guide

EVAL-LT8641A-AZ Demo Manual
65V, 3.5A/5A Peak Synchronous
Step-Down Silent Switcher
© 2023 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
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
V
VOUT
Default Output Voltage
VIN = 12V, IOUT = 0A to 3.5A
4.80
5.00
5.20
V
IOUT
Maximum Continuous
Output Current
VIN = 12V
3.50
A
fsw
Switching Frequency
1.85
2.00
2.15
MHz
Eff
Efficiency
VIN = 12V, fSW = 2MHz,
VOUT = 5V, IOUT = 1A
94
%

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
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, 1.0µF, 25V, 10%, 0603
MURATA, GRM188R71E105KA12D
6
1
C11
CAP., X7R, 4.7µF, 100V, 10% 1206
MURATA, GRM31CZ72A475ME11L
7
1
L1
IND., 2.2µH
COILCRAFT, XGL6030-222MEC
8
2
R1, R4
RES., CHIP, 1MEG, 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
U1
IC, REGULATOR, 20-QFN, UDC
ANALOG DEVICES,
LT8641ARUDCM#WPBF
Additional Evaluation Kit Components
1
1
C1
CAP., ALUM 22µF 100V
SUN ELECT, 100CE22BS
2
2
C3, C10
CAP., X7S, 4.7µF, 100V, 10%, 1210
TDK, CGA6M3X7S2A475K200AB
3
1
C9
CAP., X7R, 1.0µF, 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 1206
WURTH, 78279221281
7
1
L2 (OPT.)
IND.,
8
0
R6 (OPT.)
RES., 0603
9
1
R7
RES., CHIP, 0, 1/10W, 1%, 0604
VISHAY, CRCW06030000Z0EA
10
1
R10
RES., CHIP, 10K, 1/10W, 1%, 0603
VISHAY, CRCW060310K0FKEA
11
1
R11
RES., CHIP, 0.1Ω, 3W,1%,2512
SUSUMU, KRL3264E-C-R100-F-T1
12
1
R12
RES., CHIP, 50Ω, 1/10W, 1%, 0603
CRCW060350R0FKEA
13
1
Q1
MOSFET, N-CH,40V,14A, DPAK
VISHAY, SUD50N04-8M8P-4GE3
Hardware for Evaluation Kit Only
1
14
E2 to E10,
E12,
E15 to E17
TESTPOINT, TURRET, .094"
MILL-MAX, 2501-2-00-80-00-00-07-0
2
1
E1 (OPT.)
TESTPOINT, TURRET, .094"
3
1
JP1
DOUBLE ROW HEADER 2 x 4 .079"
SULLINS NRPN042PAEN-RC
4
1
XJP1
SHUNT, .079" CENTER
SAMTEC 2SN-BK-G
5
4
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
0
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