LT8640/LT8640-1 - 42V, 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 96% Efficiency at 1MHz
  • Up to 95% Efficiency at 2MHz
  • Wide Input Voltage Range: 3.4V to 42V
  • 5A Maximum Continuous Output, 7A 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: 100mV at 1A
  • Forced Continuous Mode (LT8640-1 Only)
  • 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
Designed for Automotive and Transportation Applications
AEC-Q100 data available for specific packages


Typical Application

LT8640 Typical Application
LT8640 Typical Application

Description

The LT®8640/LT8640-1 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 LT8640/LT8640-1 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 opendrain PG pin signals when the output is in regulation. The SYNC/MODE pin selects between Burst Mode operation, spread spectrum mode, synchronization to an external clock, and either pulse-skipping (LT8640) or forced continuous mode (LT8640-1). 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

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

Part Number Package Code Temp Package
Drawing
RoHS
LT8640EUDC-1#PBF 3x4 QFN-18 UDC E 05-08-1956 Yes
LT8640EUDC-1#TRPBF 3x4 QFN-18 UDC E 05-08-1956 Yes
LT8640EUDC#PBF 3x4 QFN-18 UDC E 05-08-1956 Yes
LT8640EUDC#TRPBF 3x4 QFN-18 UDC E 05-08-1956 Yes
LT8640HUDC#PBF 3x4 QFN-18 UDC H 05-08-1956 Yes
LT8640HUDC#TRPBF 3x4 QFN-18 UDC H 05-08-1956 Yes
LT8640IUDC-1#PBF 3x4 QFN-18 UDC I 05-08-1956 Yes
LT8640IUDC-1#TRPBF 3x4 QFN-18 UDC I 05-08-1956 Yes
LT8640IUDC#PBF 3x4 QFN-18 UDC I 05-08-1956 Yes
LT8640IUDC#TRPBF 3x4 QFN-18 UDC I 05-08-1956 Yes


LT8640 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
LT8640EUDC-1#PBF 3x4 QFN-18 E $6.22 $4.35 Yes
LT8640EUDC-1#TRPBF 3x4 QFN-18 E $4.41 Yes
LT8640EUDC#PBF 3x4 QFN-18 E $6.22 $4.35 Yes
LT8640EUDC#TRPBF 3x4 QFN-18 E $4.41 Yes
LT8640HUDC#PBF 3x4 QFN-18 H $7.20 $5.04 Yes
LT8640HUDC#TRPBF 3x4 QFN-18 H $5.10 Yes
LT8640IUDC-1#PBF 3x4 QFN-18 I $6.84 $4.79 Yes
LT8640IUDC-1#TRPBF 3x4 QFN-18 I $4.85 Yes
LT8640IUDC#PBF 3x4 QFN-18 I $6.84 $4.79 Yes
LT8640IUDC#TRPBF 3x4 QFN-18 I $4.85 Yes
Buy NowRequest Samples
* 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
DC2202A LT8640EUDC Demo Board | µPower Buck Silent Switcher, 5.7V ≤ VIN ≤ 42V; Vout = 5V @ 5A $249.00
Buy Now
Click here to view our complete list of demo boards

Designed for Automotive and Transportation Applications

AEC-Q100 data is available for these specific part numbers. Please contact your local sales representative for more information regarding reliability reports or to inquire about parts that are not included. For more information, view our Automotive and Transportation page

Part Number Package Temp Price
(1-99)
Price
(1k)*
RoHS
LT8640HUDC#PBF 3x4 QFN-18 H $7.20 $5.04 Yes
LT8640HUDC#TRPBF 3x4 QFN-18 H $5.10 Yes
LT8640IUDC#PBF 3x4 QFN-18 I $6.84 $4.79 Yes
LT8640IUDC#TRPBF 3x4 QFN-18 I $4.85 Yes
Buy NowRequest Samples
* 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.

Applications

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

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Design Tools

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:
LT8640

LTspiceIV

LTspice® IV 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 IV

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 IV
  • Step 2: Once LTspice is installed, click on the link(s) below to launch the simulation
  • Step 3: If LTspice IV 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 IV:
LT8640
LT8640-1

Technical Support