ANALOG DEVICES LT8640A Synchronous Step Down Silent Switcher User Manual
- June 16, 2024
- Analog Devices
Table of Contents
ANALOG DEVICES LT8640A Synchronous Step Down Silent Switcher
Product Information
Specifications
| Symbol | Parameter | Conditions | Min | Typ | Max | Units |
|---|---|---|---|---|---|---|
| VIN | Input Supply Range | 5.7 | 42 | V | ||
| VOUT | Output Voltage | R4 = 1M, R5 = 243k | 4.85 | 5 | 5.15 | V |
| ABOUT | Maximum Continuous Output Current | Derating Is Necessary for Certain |
VIN and Thermal
Conditions| | | 5| A
fSW| Switching Frequency| R2 = 17.8k, JP1 = FCM/SYNC| 1.85| 2| 2.15| MHz
EFF| Efficiency at DC| VIN = 12V, IOUT = 3A| 94| | | %
Product Usage Instructions
Quick Start Procedure
- Place JP1 on the BURST position.
- With power off, connect the input power supply to VEMI and GND. If EMI performance is not important, bypass the input EMI filter by connecting the input power supply to VIN and GND. With power off, connect the load from VOUT to GND.
- To read the input voltage and output voltage accurately, connect the voltage meters to VIN_SENSE and VOUT_SENSE turret pins.
- Turn on the power at the input. Note: Ensure that the input voltage does not exceed 42V.
- Check for the proper output voltage (VOUT = 5V). Note: If there is no output, temporarily disconnect the load to check if it is set too high or shorted.
- 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.
- JP1 can also be used to set LT8640A in spread spectrum mode
- (JP1 on the SPREAD-SPECTRUM position) or forced continuous mode
- (JP1 on the FCM/SYNC position). An external clock can be added to the SYNC terminal when the SYNC function is used (JP1 on the FCM/SYNC position). Ensure that R2 is chosen to set the LT8640A switching frequency equal to or below the lowest SYNC frequency.
DESCRIPTION
Demonstration circuit 3099A is a 42V, 5A synchronous step-down Silent
Switcher® with spread spectrum fre-quency modulation featuring the LT®8640A.
The demo board is designed for 5V output from a 5.7V to 42V input. Meanwhile,
the LT8640A can operate down to 3.4V inputs. The wide input range allows a
variety of input sources, such as automotive batteries and industrial
supplies. The LT8640A is a compact, ultralow emission, high efficiency, and
high speed synchronous monolithic step-down switching regulator. The
integrated power switches and inclusion of all necessary circuitry reduce the
component count and solution size. Special Silent Switcher architecture
minimizes EMI emissions. 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 30ns
enables high VIN to low VOUT conversion at high frequency. The LT8640A
switching frequency can be programmed either via an oscillator resistor or
external clock over a 200kHz to 3MHz range. The default frequency of demo
circuit 3099A is 2MHz. The LT8640A SYNC/MODE pin on the demo board is grounded
(JP1 at BURST position) by default for low ripple Burst Mode operation. Spread
spectrum mode and forced continuous mode can be selected respectively by
moving the JP1 shunt. To synchronize to an external clock, move JP1 to
FCM/SYNC and apply the external clock to the SYNC terminal.
The LT8640A 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 demo circuit 3099A. The LT8640A is assembled in a 3mm ×
4mm plastic QFN package with an exposed pad for low thermal resistance. The
layout recommendations for low EMI operation and maximum thermal performance
are available in the datasheet section Low EMI PCB Layout and Thermal
Considerations and Peak Output Current.
Design files for this circuit board are available.
All registered trademarks and trademarks are the property of their respective owners.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
SYMBOL| PARAMETER| CONDITIONS| MIN| TYP| MAX|
UNITS
---|---|---|---|---|---|---
VIN| Input Supply Range| | 5.7| | 42| V
VOUT| Output Voltage| R4 = 1MΩ, R5 = 243kΩ| 4.85| 5| 5.15| V
ABOUT| Maximum Continuous Output Current| Derating Is Necessary for Certain
VIN and Thermal Conditions| 5| A
fSW| Switching Frequency| R2 = 17.8kΩ, JP1 = FCM/SYNC| 1.85| 2| 2.15| MHz
EFF| Efficiency at DC| VIN = 12V , IOUT = 3A| 94| %
QUICK START PROCEDURE
Demonstration circuit 3099A is easy to set up to evaluate the performance of the LT8640A. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below:
- Place JP1 on BURST position.
- With power off, connect the input power supply to VEMI and GND. If the EMI performance is not important, the input EMI filter can be bypassed by connecting the input power supply to VIN and GND.
- With power off, connect the load from VOUT to GND.
- To read the input voltage and output voltage accurately, the voltage meters should be connected to VIN_SENSE and VOUT_SENSE turret pins.
- Turn on the power at the input. NOTE : Make sure that the input voltage does not exceed 42V.
- Check for the proper output voltage (VOUT = 5V). NOTE: If there is no output, temporarily disconnect the load to make sure that the load is not set too high or is shorted.
- 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, care must be taken 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 2 for the proper scope technique.
- JP1 can also set LT8640A in spread spectrum mode (JP1 on the SPREAD-SPECTRUM position) or forced continuous mode (JP1 on the FCM/SYNC position). An external clock can be added to the SYNC terminal when the SYNC function is used (JP1 on the FCM/SYNC position). Please make sure that R2 should be chosen to set the LT8640A switching frequency equal to or below the lowest SYNC frequency.
Figure 3 shows the efficiency of demo circuit 3099A at 12V input and 24V input
in Burse Mode Operation (input from VIN terminal, JP1 = BURST).
The demo board has an EMI filter installed. The EMI performance of the board
(with EMI filter) is shown on Figure 4. The red line in Figure 4 is CISPR25
Class 5 peak limit. The figure shows that the circuit passes the test with a
wide margin. To achieve EMI performance as shown in Figure 4, the input EMI
filter is required, and the input voltage should be applied at VEMI.
-
Conducted EMI Performance CISPR25 Conducted Emission Test with Class 5 Peak Limits)
-
Radiated EMI Performance (CISPR25 Radiated Emission Test with Class 5 Peak Limits)
Figure 4. LT8640A Demo Circuit 3099A EMI Performance (12V Input from VEMI, with EMI filter, IOUT = 5A)
PARTS LIST
ITEM| QTY| REFERENCE| PART DESCRIPTION| MANUFACTURER/PART NUMBER
---|---|---|---|---
Required Circuit Components
| 1 | 2 | C2, C12 | CAP., X5R, 1μF, 50V, 10%, 0603 | MURATA, GRT188R61H105KE13D |
|---|---|---|---|---|
| 2 | 2 | C4, C8 | CAP., X7R, 0.1μF, 16V, 10%, 0603 | MURATA, GRM188R71C104KA01D |
| 3 | 1 | C5 | CAP., C0G, 10pF, 25V, ±0.25pF, 0603 | AVX, 06033A100CAT2A |
| 4 | 1 | C6 | CAP., X5R, 100μF, 10V, 20% 1210 | MURATA, GRM32ER61A107ME20L |
| 5 | 2 | C7, C9 | CAP., X7R, 1μF, 25V, 10%, 0603 | MURATA, GRM188R71E105KA12D |
| 6 | 1 | C11 | CAP., X5R, 10μF, 50V, 10%, 1206 | TDK, C3216X5R1H106K160AB |
| 7 | 1 | C13 | CAP., X5R, 4.7μF, 25V, 10%, 0603 | MURATA, GRM188R61E475KE11D |
| 8 | 1 | L1 | INDUCTOR, 1.5μH | COILCRAFT, XEL6030-152ME |
| 9 | 2 | R1, R3 | RES., CHIP, 100k, 1/10W, 1% 0603 | VISHAY, CRCW0603100KFKEA |
| 10 | 1 | R2 | RES., CHIP, 17.8k, 1/10W, 1% 0603 | VISHAY, CRCW060317K8FKEA |
| 11 | 1 | R4 | RES., CHIP, 1M, 1/10W, 1%, 0603 | VISHAY, CRCW06031M00FKEA |
| 12 | 1 | R5 | RES., CHIP, 243k, 1/10W, 1%, 0603 | VISHAY, CRCW0603243KFKEA |
| 13 | 1 | U1 | I.C., STEP-DOWN SILENT SWITCHER, QFN-18 | ANALOG DEVICES, |
LT8640AJUDCM#PBF
Additional Demo Board Circuit Components
| 1 | 1 | C1 | CAP., ALUM 22μF, 63V | SUN ELECT., 63CE22BS |
|---|---|---|---|---|
| 2 | 2 | C3, C10 | CAP., X7R, 10μF, 50V, 10%, 1210 | MURATA, GRM32ER71H106KA12L |
| 3 | 1 | C14 | CAP., X7R, 0.1μF, 50V, 10%, 0402 | MURATA, GRM155R71H104KE14D |
| 4 | 0 | C19 (OPT) | CAP., OPTION, 0805 | |
| 5 | 1 | FB1 | BEAD, FERRITE, 100Ω AT 100MHz, 8A, 1812 | WURTH ELEKTRONIK, |
74279226101
6| 0| L2| IND., OPT, XAL60XX|
7| 1| Q1| MOSFET, N-CH, 40V, 14A, DPAK (TO-252)| VISHAY, SUD50N04-8M8P-4GE3
8| 0| R6 (OPT)| RES., OPTION, 0603|
9| 2| R7, R12| RES., CHIP, 0Ω, 1/10W, 1%, 0603| VISHAY, CRCW06030000Z0EA
10| 1| R10| RES., CHIP, 10k, 1/10W, 1% 0603| VISHAY, CRCW060310K0FKEA
11| 1| R11| RES., 0.1Ω, 1%, 3W, 2512, SHORT-SIDE TERMINAL| SUSUMU,
KRL3264E-C-R100-F-T1
Hardware: For Demo Board Only
1| 9| E1, E5-E9, E15-E17| TESTPOINT, TURRET, 0.094″| MILL-MAX,
2501-2-00-80-00-00-07-0
---|---|---|---|---
2| 4| E2, E3, E4, E10| TESTPOINT, TURRET, 0.064″| MILL-MAX,
2308-2-00-80-00-00-07-0
3| 4| J1-J4| JACK BANANA| KEYSTONE, 575-4
4| 1| JP1| 2X3, 0.079 DOUBLE ROW HEADER| WURTH ELEKTRONIK, 62000621121
5| 4| MP1-MP4| STANDOFF, NYLON, SNAP-ON, 11.1mm| WURTH ELEKTRONIK, 702934000
6| 1| XJP1| SHUNT, 0.079″ CENTER| WURTH ELEKTRONIK, 60800213421
SCHEMATIC DIAGRAM
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
By using the evaluation board discussed herein (together with any tools, components documentation or support materials, the “Evaluation Board”), you are agreeing to be bound by the terms and 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
- rent, lease, display, sell, transfer, assign, sublicense, or distribute the Evaluation Board; and
- permit any Third Party to access the Evaluation Board. As used herein, the term “Third Party” includes any entity other than ADI, Customer, their employees, affiliates, and in-house consultants. The Evaluation Board is NOT sold to Customer; all rights not expressly granted herein, including ownership of the Evaluation Board, are reserved by ADI. CONFIDENTIALITY. This Agreement and the Evaluation Board shall all be considered the confidential and proprietary information of ADI. The customer may not disclose or transfer any portion of the Evaluation Board to any other party for any reason. Upon discontinuation of use of the Evaluation Board or termination of this Agreement, Customer agrees to promptly return the Evaluation Board to ADI. ADDITIONAL RESTRICTIONS. Customers may not disassemble, decompile, or reverse engineer chips on the Evaluation Board. The customer shall inform ADI of any occurred damages or any modifications or alterations it makes to the Evaluation Board, including but not limited to soldering or any other activity that affects the material content of the Evaluation Board. Modifications to the Evaluation Board must comply with applicable law, including but not limited to the RoHS Directive. TERMINATION. ADI may terminate this Agreement at any time upon giving written notice to Customer. The customer agrees to return to ADI the Evaluation Board at that time. LIMITATION OF LIABILITY. THE EVALUATION BOARD PROVIDED HEREUNDER IS PROVIDED “AS IS” AND ADI MAKES NO WARRANTIES OR REPRESENTATIONS OF ANY KIND WITH RESPECT TO IT. ADI SPECIFICALLY DISCLAIMS ANY REPRESENTATIONS, ENDORSEMENTS, GUARANTEES, OR WARRANTIES, EXPRESS OR IMPLIED, RELATED TO THE EVALUATION BOARD INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTY OF MERCHANTABILITY, TITLE, FITNESS FOR A PARTICULAR PURPOSE OR NONINFRINGEMENT OF INTELLECTUAL PROPERTY RIGHTS. IN NO EVENT WILL ADI AND ITS LICENSORS BE LIABLE FOR ANY INCIDENTAL, SPECIAL, INDIRECT, OR CONSEQUENTIAL DAMAGES RESULTING FROM THE CUSTOMER’S POSSESSION OR USE OF THE EVALUATION BOARD, INCLUDING BUT NOT LIMITED TO LOST PROFITS, DELAY COSTS, LABOR COSTS, OR LOSS OF GOODWILL. ADI’S TOTAL LIABILITY FROM ANY AND ALL CAUSES SHALL BE LIMITED TO THE AMOUNT OF ONE HUNDRED US DOLLARS ($100.00). EXPORT. The customer agrees that it will not directly or indirectly export the Evaluation Board to another country and that it will comply with all applicable United States federal laws and regulations relating to exports. GOVERNING LAW. This Agreement shall be governed by and construed in accordance with the substantive laws of the Commonwealth of Massachusetts (excluding conflict of law rules). Any legal action regarding this Agreement will be heard in the state or federal courts having jurisdiction in Suffolk County, Massachusetts, and Customer hereby submits to the personal jurisdiction and venue of such courts. The United Nations Convention on Contracts for the International Sale of Goods shall not apply to this Agreement and is expressly disclaimed.