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  4. Step-Down (Buck) Regulators
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  6. LTC3857

Data Sheet
JP
User Guides
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Overview

Features and Benefits

  • Low Operating IQ: 50μA (One Channel On)
  • Wide Output Voltage Range: 0.8V ≤ VOUT ≤ 24V
  • Wide VIN Range: 4V to 38V (40V Abs Max)
  • RSENSE or DCR Current Sensing
  • Out-of-Phase Controllers Reduce Required Input Capacitance and Power Supply Induced Noise
  • OPTI-LOOP® Compensation Minimizes COUT
  • Phase-Lockable Frequency (75kHz-850kHz)
  • Programmable Fixed Frequency (50kHz-900kHz)
  • Selectable Continuous, Pulse-Skipping or Low Ripple Burst Mode® Operation at Light Loads
  • Selectable Current Limit
  • Very Low Dropout Operation: 99% Duty Cycle
  • Adjustable Output Voltage Soft-Start or Tracking
  • Power Good Output Voltage Monitors
  • Output Overvoltage Protection
  • Low Shutdown IQ : <8μA
  • Internal LDO Powers Gate Drive from VIN or EXTVCC
  • No Current Foldback During Start-up
  • 5mm × 5mm QFN Package

Product Details

The LTC3857 is a high performance dual step-down switching regulator controller that drives all N-channel synchronous power MOSFET stages. A constant frequency current mode architecture allows a phase-lockable frequency of up to 850kHz. Power loss and noise due to the ESR of the input capacitor ESR are minimized by operating the two controller output stages out of phase.

The 50μA no-load quiescent current extends operating run time in battery-powered systems. The LTC3857 features a precision 0.8V reference and power good output indicators. A wide 4V to 38V input supply range encompasses a wide range of intermediate bus voltages and battery chemistries.

Independent TRACK/SS pins for each controller ramp the output voltages during start-up. Current foldback limits MOSFET heat dissipation during short-circuit conditions. The PLLIN/MODE pin selects among Burst Mode operation, pulse-skipping mode, or continuous inductor current mode at light loads.

For a leaded 28-lead SSOP package with a fixed current limit and one PGOOD output, without phase modulation or a clock output, see the LTC3857-1 data sheet.


   LTC3857 LTC3857-1
Features   Adjustable Current Limit, Clock Output, Phase Modulation, 2 PGOOD Outputs Fixed Current Limit, One PGOOD Output
Package QFN-32 SSOP-28

Applications

  • Automotive Always-On Systems
  • Battery Operated Digital Devices
  • Distributed DC Power Systems

Product Categories

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At least one model within this product family is in production and available for purchase. The product is appropriate for new designs but newer alternatives may exist.

Evaluation Kits (1)

Documentation & Resources

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  • Data Sheets (1)
  • Reliability Data (1)
  • User Guides (1)
  • Technical Articles (2)
    • Document Type

    Tools & Simulations

    LTspice

    LTspice® is a powerful, fast and free simulation software, schematic capture and waveform viewer with enhancements and models for improving the simulation of analog circuits.

    To launch ready-to-run LTspice demonstration circuits for this part:

    Step 1: Download and install LTspice on your computer.

    Step 2: Click on the link in the section below to download a demonstration circuit.

    Step 3: If LTspice does not automatically open after clicking the link below, 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.

    LTspice

    LTspice Simulations

    LTC3857 Demo Circuit - Dual Synchronous Step-Down (4.5-36V to 3.3V @ 5A & 8.5V @ 3A)

    Models for the following parts are available in LTspice:

    LTC3857
    LTC3857-1

    LTpowerCAD

    LTpowerCAD® is a power supply design program which selects power stage components, provides detailed power efficiency, shows quick loop Bode plot stability and load transient analysis, and can export to LTspice for simulation.

    To open the project file for this circuit:

    Step 1: Download and install LTpowerCAD on your computer.

    Step 2: Click on the link(s) in the section below to download part-specific project files.

    Step 3: If the project file doesn't run, right-click the link and select "Save Target As." Then start the LTpowerCAD tool and open the project file by selecing "Open Project" from the "File" menu.

    LTPowerCAD

    LTpowerCAD Project Files

    LTC3857 Project - Low IQ, Dual, 2-Phase Synchronous Step-Down Supply (9-36V to 3.3 @ 5A & 8.5 @ 3A)

    Design tools for the following parts are available in LTpowerCAD:

    LTC3857
    LTC3857-1

    Product Recommendations

    LTC3857 Companion Parts

    Recommended Related Parts

    Design Resources

    ADI has always placed the highest emphasis on delivering products that meet the maximum levels of quality and reliability. We achieve this by incorporating quality and reliability checks in every scope of product and process design, and in the manufacturing process as well.  "Zero defects" for shipped products is always our goal.View our quality and reliability program and certifications for more information.

    Part Number Material Declaration Reliability Data Pin/Package Drawing CAD Symbols, Footprints & 3D Models
    LTC3857EUH#PBF Material Declaration Reliability Data 32-Lead QFN (5mm x 5mm x 0.75mm w/ EP)
    LTC3857EUH#TRPBF Material Declaration Reliability Data 32-Lead QFN (5mm x 5mm x 0.75mm w/ EP)
    LTC3857IUH#PBF Material Declaration Reliability Data 32-Lead QFN (5mm x 5mm x 0.75mm w/ EP)
    LTC3857IUH#TRPBF Material Declaration Reliability Data 32-Lead QFN (5mm x 5mm x 0.75mm w/ EP)
    Wafer Fabrication Data R526 Reliability Data

    PCN-PDN Information

    Select a model from the dropdown below to subscribe to PCN/PDN notifications and view past notifications as well.

    Select Model for PCN Information
    • LTC3857EUH#PBF Production
    • LTC3857EUH#TRPBF Production
    • LTC3857IUH#PBF Production
    • LTC3857IUH#TRPBF Production

    Support & Discussions

    LTC3857 Discussions

    RE: Question about LTC7851
    All LTC3857 Discussions
    LTC3857 Contact ADI Technical Support »
    LTC3857 Ask your question »
    LTC3857 Contact ADI Technical Support » LTC3857 Ask your question »

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