Features and Benefits
- Operates with Power Blocks, DrMOS or External Gate Drivers and MOSFETs
- Constant-Frequency Voltage Mode Control with Accurate Current Sharing
- ±0.75% 0.6V Voltage Reference
- Dual Differential Output Voltage Sense Amplifiers
- Multiphase Capability—Up to 12-Phase Operation
- Programmable Current Limit
- Safely Powers a Prebiased Load
- Programmable or PLL-Synchronizable Switching Frequency Up to 2.25MHz
- Lossless Current Sensing Using Inductor DCR or Precision Current Sensing with Sense Resistor
- VCC Range: 3V to 5.5V
- VIN Range: 3V to 24V
- Power Good Output Voltage Monitor
- Output Voltage Tracking Capability
- Programmable Soft-Start
- Available in a 36-Pin 5mm × 6mm QFN Package
The LTC3861 is a dual PolyPhase® synchronous stepdown switching regulator controller for high current distributed power systems, digital signal processors, and other telecom and industrial DC/DC power supplies. It uses a constant-frequency voltage mode architecture combined with very low offset, high bandwidth error amplifiers and a remote output sense differential amplifier per channel for excellent transient response and output regulation.
The controller incorporates lossless inductor DCR current sensing to maintain current balance between phases and to provide overcurrent protection. The chip operates from a VCC supply between 3V and 5.5V and is designed for stepdown conversion from VIN between 3V and 24V to output voltages between 0.6V and VCC – 0.5V.
The TRACK/SS pins provide programmable soft-start or tracking functions. Inductor current reversal is disabled during soft-start to safely power prebiased loads. The constant operating frequency can be synchronized to an external clock or linearly programmed from 250kHz to 2.25MHz. Up to six LTC3861 controllers can operate in parallel for 1-, 2-, 3-, 4-, 6- or 12-phase operation.
The LTC3861 is available in a 36-pin 5mm × 6mm QFN package. LTC3861-1 is a 32-pin QFN version of the LTC3861, which has a single differential remote output voltage sense amplifier.
|# Diff Amps||Config Pin||Package|
|LTC3861||2||Yes||5 x 6 QFN-36|
|LTC3861-1||1||No||5 x 5 QFN-32|
- High Current Distributed Power Systems
- DSP, FPGA and ASIC Supplies
- Datacom and Telecom Systems
- Industrial Power Supplies
Product Lifecycle Recommended for New Designs
This product has been released to the market. The data sheet contains all final specifications and operating conditions. For new designs, ADI recommends utilization of these products.
Evaluation Kits (1)
Demonstration circuit 1822B is a dual output synchronous buck converter featuring the LTC3861EUHE. The board provides two outputs of 1.5V/25A and 1.2V/25A from an input voltage of 7V to 14V at a switching frequency of 500kHz. The power stage consists of a 6mm × 6mm DrMOS and a 13mm × 13mm iron powder type inductor. An on-board 5V LT3470 buck regulator provides the 5V bias for the LTC3861 and the DrMOS.
The demo board uses a high density, two sided drop-in layout. The power components, excluding the bulk output and input capacitors, fit within a 1.5" × 1.2" area on the top layer. The control circuit fits in a 1.1" × 1.0" area on the bottom layer. The package style for the LTC3861EUHE is a 36-lead 5mm × 6mm QFN.
Features & Benefits
- Remote sensing for each output, where the divider is placed before a high input impedance differential amplifier.
- CLKIN and CLKOUT pins.
- Optional resistors to tie the two outputs together.
- Connector and header to tie two or more boards together for up to 12-phase operation.
- Optional footprint for an LTC4449 gate driver and discrete MOSFETs.
- Optional footprint for a dual phase Delta power block.
Documentation & Resources
R415 Reliability Data3/23/2018
DC1822A - Demo Manual6/14/2012
How Monolithic Driver + MOSFET (DrMOS) Technology Improves Power System Design6/1/2022 Analog Dialogue
Sub-Milliohm DCR Current Sensing with Accurate Multiphase Current Sharing for High Current Power Supplies1/1/2013 LT Journal
Tools & Simulations
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.
Models for the following parts are available in LTspice:
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.
Design tools for the following parts are available in LTpowerCAD:
LTC3861 Companion Parts
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|
|LTC3861EUHE#PBF||Material Declaration||Reliability Data||36-Lead QFN (5mm x 6mm x 0.75mm w/ EP)|
|LTC3861EUHE#TRPBF||Material Declaration||Reliability Data||36-Lead QFN (5mm x 6mm x 0.75mm w/ EP)|
|LTC3861IUHE#PBF||Material Declaration||Reliability Data||36-Lead QFN (5mm x 6mm x 0.75mm w/ EP)|
|LTC3861IUHE#TRPBF||Material Declaration||Reliability Data||36-Lead QFN (5mm x 6mm x 0.75mm w/ EP)|
|Wafer Fabrication Data||R415 Reliability Data|
Sample & Buy
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Pricing displayed is based on 1-piece. The USA list pricing shown is for budgetary use only, shown in United States dollars (FOB USA per unit), and is subject to change. International prices may vary due to local duties, taxes, fees and exchange rates.