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LT8640/LT8640-1 - 42V, 5A Synchronous Step-Down Silent Switcher with 2.5μA Quiescent Current

LT4363 - High Voltage Surge Stopper with Current Limit

LT8641 - 65V, 3.5A Synchronous Step-Down Silent Switcher with 2.5μA Quiescent Current

Features

  • Silent Switcher® Architecture
  • Ultralow EMI/EMC Emissions
  • Spread Spectrum Frequency Modulation
  • High Efficiency at High Frequency
  • Up to 95% Efficiency at 1MHz
  • Up to 94% Efficiency at 2MHz
  • Wide Input Voltage Range: 3V to 65V
  • 3.5A Maximum Continuous Output,
  • 5A Peak Transient Output
  • Ultralow Quiescent Current Burst Mode® Operation
  • 2.5μA IQ Regulating 12VIN to 3.3VOUT
  • Output Ripple < 10mVP-P
  • Fast Minimum Switch-On Time: 35ns
  • Low Dropout Under All Conditions: 130mV at 1A
  • Safely Tolerates Inductor Saturation in Overload
  • Adjustable and Synchronizable: 200kHz to 3MHz
  • Peak Current Mode Operation
  • Output Soft-Start and Tracking
  • Small 18-Lead 3mm × 4mm QFN

Typical Application

LT8641 Typical Application
LT8641 Typical Application

Description

The LT®8641 step-down regulator features Silent Switcher architecture designed to minimize EMI/EMC emissions while delivering high efficiency at frequencies up to 3MHz. Assembled in a 3mm × 4mm QFN, the monolithic construction with integrated power switches and inclusion of all necessary circuitry yields a solution with a minimal PCB footprint. An ultralow 2.5μA quiescent current—with the output in full regulation—enables applications requiring highest efficiency at very small load currents. Transient response remains excellent and output voltage ripple is below 10mVP-P at any load, from zero to full current.

The LT8641 allows high VIN to low VOUT conversion at high frequency with a fast minimum top switch on-time of 35ns. Operation is safe in overload even with a saturated inductor.

Essential features are included and easy to use: An open-drain PG pin signals when the output is in regulation. The SYNC/MODE pin selects between Burst Mode, pulse-skipping, or spread spectrum mode, and also allows synchronization to an external clock. Soft-start and tracking functionality is accessed via the TR/SS pin. An accurate enable threshold can be set using the EN/UV pin and a resistor at the RT pin programs switch frequency.

Packaging

CAD Symbols and Footprints: The downloadable Zip file below contains the schematic symbol and PCB footprints.

For complete and up to date package information and drawings, please refer to our packaging page

Part Number Package Code Temp Package
Drawing		 RoHS
LT8641EUDC#PBF 3x4 QFN-18 UDC E 05-08-1956 Yes
LT8641EUDC#TRPBF 3x4 QFN-18 UDC E 05-08-1956 Yes
LT8641IUDC#PBF 3x4 QFN-18 UDC I 05-08-1956 Yes
LT8641IUDC#TRPBF 3x4 QFN-18 UDC I 05-08-1956 Yes


LT8641 Package Drawing

Order Info

  • Part numbers ending in PBF are lead free. Solder plated terminal finish (SnPb) versions are non-standard and special terms and conditions and pricing applies if available. Please contact LTC marketing for information.
  • Part numbers containing TR or TRM are shipped in tape and reel or 500 unit mini tape and reel, respectively
  • Please refer to our general ordering information or the product datasheet for more details

Package Variations and Pricing

Part Number Package Temp Price
(1-99)		 Price
(1k)*		 RoHS
LT8641EUDC#PBF 3x4 QFN-18 E $6.22 $4.35 Yes
LT8641EUDC#TRPBF 3x4 QFN-18 E $6.28 $4.41 Yes
LT8641IUDC#PBF 3x4 QFN-18 I $6.84 $4.79 Yes
LT8641IUDC#TRPBF 3x4 QFN-18 I $6.90 $4.85 Yes
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* The USA list pricing shown is for BUDGETARY USE ONLY, shown in United States dollars (FOB USA per unit for the stated volume), and is subject to change. International prices may differ due to local duties, taxes, fees and exchange rates. For volume-specific price or delivery quotes, please contact your local Linear Technology sales office or authorized distributor.

Demo Boards

Linear Technology offers many demo boards free of charge to qualified customers. Contact your local sales office or distributor to inquire about a demo board. Certain demo boards are also available for sale via credit card on this website. Demo boards are for evaluation purposes only. It remains the customer’s responsibility to verify proper and reliable operation in the actual end application.

Part Number Description Price Documentation
DC2373A LT8641 Demo Board | Sync Buck, Silent Switcher, 5.5V ≤ VIN ≤ 65V, Vout = 5V @ 3.5A, fSW = 2MHz $249.00
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Click here to view our complete list of demo boards

Applications

  • Automotive and Industrial Supplies
  • General Purpose Step-Down
  • GSM Power Supplies

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Design Tools

LTspice

LTspice® software is a powerful, fast and free simulation tool, schematic capture and waveform viewer with enhancements and models for improving the simulation of switching regulators. Click here to download LTspice

To launch a ready to run LTspice demonstration circuit for this part:

  • Step 1: If you have not installed LTspice on this computer, download and install LTspice
  • Step 2: Once LTspice is installed, click on the link(s) below to launch the simulation
  • Step 3: If LTspice does not automatically open after clicking the link above, you can instead run the simulation by right clicking on the link and selecting "Save Target As." After saving the file to your computer, start LTspice and open the demonstration circuit by selecting 'Open' from the 'File' menu

To explore other ready to run LTspice demonstration circuits, please visit our Demo Circuits Collection.

Models for the following parts are available in LTspice:
LT8641

LTpowerCAD

The LTpowerCAD design tool is a complete power supply design tool program that can significantly ease the tasks of power supply design. It guides users to a solution, selects power stage components, provides detailed power efficiency, shows quick loop bode plot stability and load transient analysis, and can export a final design to LTspice for simulation. Click here to download LTpowerCAD

To open the project file for this circuit:

  • Step 1: If you have not installed LTpowerCAD on this computer, download and install LTpowerCAD
  • Step 2: Once LTpowerCAD is installed, click on the link(s) below to open the project file
  • Step 3: If LTpowerCAD does not automatically open after clicking the link above, you can open the project file by right clicking on the link and selecting "Save Target As." After saving the file to your computer, start LTpowerCAD and open the project file by selecting 'Open Project' from the 'File' menu

Design tools for the following parts are available in LTpowerCAD:
LT8641

Technical Support