ANALOG DEVICES EVAL-LT8641A-AZ Peak Synchronous Step Down Silent Switcher Instruction Manual
- June 16, 2024
- Analog Devices
Table of Contents
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 EVALLT8641A-AZ. The LT8641Ais assembled ina 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| I TYP| I
MAX| UNITS
---|---|---|---|---|---|---
VIN| Input Voltage Range| | 5.50| | 65.00| V
VOUT| Default Output Voltage| VIN = 12V, lout = OA to 3.5A| 4.80| 5.00| 5.20|
V
I OUT| 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, lour = 1et| 94| | | %
© 2023 Analog Devices, Inc. All rights reserved. Trademarks and registered trademarks are the property of their respective owners.
Typical Performance Characteristics
Figure 2. LT8641A Eval Circuit Conducted and Radiated EMI Performance in CISPR25 Emission Test (VEMI = 14V, VOUT = 5V, IOUT = 3.5A, 2MHz Switching Frequency)
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.
-
Set an input power supply capable of 65V/5A.
-
With power off, connect the input power supply to VEMI and GND.
-
With power off, connect the loads from VOUT to GND.
-
Place the voltmeters across the output voltage sense terminals VOUT_SENSE and GND to get accurate output voltage measurements.
-
Turn on the power at the input.
Note: Make sure that the input voltage does not exceed 65V. -
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. -
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. -
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”.
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)
Schematic Diagram
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.
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