LTC3857

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Low IQ, Dual, 2-Phase Synchronous Step-Down Controller

Data Sheet Product Selection Table
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Overview

  • 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

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
LTC3857
Low IQ, Dual, 2-Phase Synchronous Step-Down Controller
High Efficiency Dual 3.3V/8.5V Step-Down Converter Efficiency and Power Loss vs Output Current Product Package 1
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Documentation

Data Sheet 1

Reliability Data 1

User Guide 1

Technical Articles 2

Data Sheet

This is the most up-to-date revision of the Data Sheet.

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Software Resources

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Hardware Ecosystem

Parts Product Life Cycle Description
Circuit Monitors 1
LTC2960
RECOMMENDED FOR NEW DESIGNS 36V Nano-Current Two-Input Voltage Monitor
Protection Switches & Controllers 2
LTC4364
RECOMMENDED FOR NEW DESIGNS Surge Stopper with Ideal Diode
LTC2955
RECOMMENDED FOR NEW DESIGNS Pushbutton On/Off Controller with Automatic Turn-On
Switching Regulators & Controllers 1
LTC3880
RECOMMENDED FOR NEW DESIGNS Dual Output PolyPhase Step-Down DC/DC Controller with Digital Power System Management
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Tools & Simulations

LTspice 1

Models for the following parts are available in LTspice:

  • LTC3857
  • LTC3857-1

LTpowerCAD 1

Design tools for the following parts are available in LTpowerCAD:

  • LTC3857
  • LTC3857-1
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.

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.

Evaluation Kits

eval board
schematic 1
DC1381A-A

LTC3857IUH Demo Board | 4.5V ≤ VIN ≤ 36V, VOUT1 = 3.3V @ 5A, VOUT2 = 8.5V @ 3A

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Product Details

Demonstration circuit 1381A is a Low Quiescent Current, Dual Output Synchronous Buck Converter featuring the LTC3857EUH/LTC3858EUH. The DC1381A provides 3.3V/5A and 8.5V/3A from a wide input voltage range of 4.5V to 36V, making it suitable for automotive or other battery fed application where low quiescent current is important.


Two versions of the board are available. DC-1381A-A is for the LTC3857EUH, while the DC1381A-B is for the LTC3858EUH. The LTC3857EUH offers lower quiescent current and smaller burst mode ripple, while the LTC3858EUH offers latch-off protection and increased burst mode efficiency.
DC1381A-A
LTC3857IUH Demo Board | 4.5V ≤ VIN ≤ 36V, VOUT1 = 3.3V @ 5A, VOUT2 = 8.5V @ 3A
DC1381A-A - Schematic

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