LTC3126 - 42V, 2.5A Synchronous Step-Down Regulator with No-Loss Input PowerPath


  • Seamless, Automatic Transition Between Two Input Power Sources
  • Wide Input Voltage Range: 2.4V to 42V
  • Wide Output Voltage Range: 0.818V to VIN
  • Up to 2.5A Continuous Output Current
  • Pin Selectable Priority and Ideal Diode-OR Modes
  • Burst Mode® Operation, IQ = 2μA
  • 95% Efficiency at 1A, VIN = 12V, VOUT = 5V
  • 1μA Current in Shutdown
  • Programmable Input UVLO Thresholds
  • Input Valid, Priority Channel and PGOOD Indicators
  • 200kHz to 2.2MHz Fixed Frequency PWM
  • Synchronizable to an External Clock
  • Current Mode Control with 60ns Minimum On-Time
  • Minimal External Components
  • Thermally Enhanced 28-Lead 4mm × 5mm QFN and 28-Lead TSSOP Packages

Typical Application

LTC3126 Typical Application
LTC3126 Typical Application


The LTC®3126 is a high efficiency synchronous buck converter with an internal no-loss PowerPath™ supporting seamless operation from two separate input power sources. Pin selectable ideal diode-OR and priority input modes with user programmable undervoltage lockout thresholds provide full control over the transition between the input power sources. The fast, automatic switchover provided by the internal PowerPath eliminates the need for hold-up capacitors and minimizes disturbances on the output rail. An active input channel indicator and independent input and output power good signals provide complete feedback of the power system status.

A wide 2.4V to 42V input voltage range, 2.5A output current capability and 2μA Burst Mode operation quiescent current facilitate use of the LTC3126 with a wide variety of power sources including supercapacitors, automotive batteries, unregulated wall adapters and single to multi-cell stacks of most battery chemistries. Additional features include 1μA current in shutdown, internal softstart and thermal protection. The LTC3126 is available in thermally enhanced 28-lead 4mm × 5mm QFN and 28-lead TSSOP packages.


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
LTC3126EFE#PBF TSSOP-28 FE E 05-08-1663 (EB) Yes
LTC3126EFE#TRPBF TSSOP-28 FE E 05-08-1663 (EB) Yes
LTC3126EUFD#PBF 4x5 QFN-28 UFD E 05-08-1712 Yes
LTC3126EUFD#TRPBF 4x5 QFN-28 UFD E 05-08-1712 Yes
LTC3126HFE#PBF TSSOP-28 FE H 05-08-1663 (EB) Yes
LTC3126HFE#TRPBF TSSOP-28 FE H 05-08-1663 (EB) Yes
LTC3126IFE#PBF TSSOP-28 FE I 05-08-1663 (EB) Yes
LTC3126IFE#TRPBF TSSOP-28 FE I 05-08-1663 (EB) Yes
LTC3126IUFD#PBF 4x5 QFN-28 UFD I 05-08-1712 Yes
LTC3126IUFD#TRPBF 4x5 QFN-28 UFD I 05-08-1712 Yes

LTC3126 Package Drawing
LTC3126 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
LTC3126EFE#PBF TSSOP-28 E $9.29 $6.50 Yes
LTC3126EFE#TRPBF TSSOP-28 E $9.35 $6.56 Yes
LTC3126EUFD#PBF 4x5 QFN-28 E $8.93 $6.25 Yes
LTC3126EUFD#TRPBF 4x5 QFN-28 E $8.99 $6.31 Yes
LTC3126HFE#PBF TSSOP-28 H $10.57 $7.40 Yes
LTC3126HFE#TRPBF TSSOP-28 H $10.63 $7.46 Yes
LTC3126IFE#PBF TSSOP-28 I $10.22 $7.15 Yes
LTC3126IFE#TRPBF TSSOP-28 I $10.28 $7.21 Yes
LTC3126IUFD#PBF 4x5 QFN-28 I $9.83 $6.88 Yes
LTC3126IUFD#TRPBF 4x5 QFN-28 I $9.89 $6.94 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
DC2215A LTC3126EUFD Demo Board | Dual Input Sync Buck, 4.3V ≤ VIN1 ≤ 42V, 6V ≤ VIN2 ≤ 8.4V (Operational to 42V), VOUT = 3.3V @ 2.5A Contact Factory
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Click here to view our complete list of demo boards


  • Portable Industrial/Communications Test Equipment
  • Battery and Supercapacitor Backup Power
  • Automotive Power with Battery Backup
  • Uninterruptible Power Supplies

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