LTC3605A - 20V, 5A Synchronous Step-Down Regulator


  • High Efficiency: Up to 96%
  • 5A Output Current
  • 4V to 20V VIN Range
  • Integrated Power N-Channel MOSFETs (70mΩ Top and 35mΩ Bottom)
  • Adjustable Frequency 800kHz to 4MHz
  • PolyPhase® Operation (Up to 12 Phases)
  • Output Tracking
  • 0.6V ±1% Reference Accuracy
  • Current Mode Operation for Excellent Line and Load Transient Response
  • Shutdown Mode Draws Less Than 15μA Supply Current
  • LTC3605: 15V Absolute Maximum VIN
  • LTC3605A: 22V Absolute Maximum VIN
  • The LTC3605A Is Pin Compatible with the LTC3605
  • Available in 24-Pin (4mm × 4mm) QFN Package

Typical Application

LTC3605A Typical Application
LTC3605A Typical Application


The LTC®3605A is a high efficiency, monolithic synchronous buck regulator using a phase lockable controlled on-time constant frequency, current mode architecture. PolyPhase operation allows multiple LTC3605A regulators to run out of phase while using minimal input and output capacitance. The operating supply voltage range is from 20V down to 4V, making it suitable for dual, triple or quadruple lithium-ion battery inputs as well as point of load power supply applications from a 12V or 5V rail.

The operating frequency is programmable from 800kHz to 4MHz with an external resistor. The high frequency capability allows the use of small surface mount inductors. For switching noise sensitive applications, it can be externally synchronized from 800kHz to 4MHz. The PHMODE pin allows user control of the phase of the outgoing clock signal. The unique constant frequency/controlled on-time architecture is ideal for high step-down ratio applications that are operating at high frequency while demanding fast transient response. Two internal phase-lock loops synchronize the internal oscillator to the external clock and also servos the regulator on-time to lock on to either the internal clock or the external clock if it’s present.

  Input Voltage Range 
LTC3605 4V to 15V
LTC3605A 4V to 20V


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
LTC3605AEUF#PBF 4x4 QFN-24 UF E 05-08-1697 Yes
LTC3605AEUF#TRPBF 4x4 QFN-24 UF E 05-08-1697 Yes
LTC3605AIUF#PBF 4x4 QFN-24 UF I 05-08-1697 Yes
LTC3605AIUF#TRPBF 4x4 QFN-24 UF I 05-08-1697 Yes

LTC3605A 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
LTC3605AEUF#PBF 4x4 QFN-24 E $6.07 $4.25 Yes
LTC3605AEUF#TRPBF 4x4 QFN-24 E $4.31 Yes
LTC3605AIUF#PBF 4x4 QFN-24 I $7.14 $5.00 Yes
LTC3605AIUF#TRPBF 4x4 QFN-24 I $5.06 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
DC1897B LTC3605A Demo Board | 4V to 20V Input, Vout = 2.5V/3.3V/5V/Adj @ 5A $150.00
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Click here to view our complete list of demo boards


  • Point of Load Power Supply
  • Portable Instruments
  • Distributed Power Systems
  • Battery-Powered Equipment

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Design Tools


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:


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:

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