Features and Benefits
- Dual, 180° Phased Controllers Reduce Required Input Capacitance and Power Supply Induced Noise
- High Efficiency: Up to 95%
- RSENSE or DCR Current Sensing
- Programmable DCR Temperature Compensation
- ±0.75% 0.6V Output Voltage Accuracy
- Phase-Lockable Fixed Frequency 250kHz to 770kHz
- True Remote Sensing Differential Amplifier
- Dual N-Channel MOSFET Synchronous Drive
- Wide VIN Range: 4.5V to 38V
- VOUT Range: 0.6V to 12.5V without Differential Amplifier
- VOUT Range: 0.6V to 3.3V with Differential Amplifier
- Clock Input and Output for Up to 12-Phase Operation
- Adjustable Soft-Start or VOUT Tracking
- Foldback Output Current Limiting
- Output Overvoltage Protection
- 40-Pin (6mm × 6mm) QFN and 38-Lead FE Packages
The LTC3855 is a dual PolyPhase® current mode synchronous step-down switching regulator controller that drives all N-channel power MOSFET stages. It includes a high speed differential remote sense amplifier. The maximum current sense voltage is programmable for either 30mV, 50mV or 75mV, allowing the use of either the inductor DCR or a discrete sense resistor as the sensing element.
The LTC3855 features a precision 0.6V reference and can produce output voltages up to 12.5V. A wide 4.5V to 38V input supply range encompasses most intermediate bus voltages and battery chemistries. Power loss and supply noise are minimized by operating the two controller output stages out of phase. Burst Mode® operation, continuous or pulse-skipping modes are supported.
The LTC3855 can be configured for up to 12-phase operation, has DCR temperature compensation, two power good signals and two current limit set pins. The LTC3855 is available in low profile 40-pin 6mm × 6mm QFN and 38-lead exposed pad FE packages.
- Computer Systems
- Telecom Systems
- Industrial and Medical Instruments
- DC Power Distribution Systems
Product Lifecycle Production
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 (4)
Demonstration circuit DC1617A is a dual output synchronous buck converter featuring the LTC3855EFE in a high density, two sided drop-in layout with power components on the top and the control circuit on the bottom. The package style for the LTC3855EFE is a 38-lead TSSOP. The board comes in two assembly types. The –B assembly is a high power, 12V/6A and 5V/10A converter with a 13V to 36V input. A sense resistor is used to provide a precise current limit. Unlike the –A assembly, on the –B assembly the remote sense diff amp is bypassed since VOUT2 is > 3.3V.
Demonstration circuit DC1617A is a dual output synchronous buck converter featuring the LTC3855EFE in a high density, two sided drop-in layout with power components on the top and the control circuit on the bottom. The package style for the LTC3855EFE is a 38-lead TSSOP. The board comes in two assembly types. The –A assembly provides 2.5V/15A and 1.8V/15A from a 4.5V to 26V input. DCR inductor sensing is used to provide the highest efficiency. The current limit is NTC compensated to provide the minimal amount of variation over temperature. The -A also features remote sensing for VOUT2.
Demonstration circuit 1586A is a high efficiency, dual-output (3.3V and 2.5V), synchronous buck converter with 4.5V to 25V input range. It can supply 5A maximum load current at 3.3V and 2.5V outputs. The demo board uses the LTC3855EUJ controller. The LTC3855 is a feature-rich dual-output dual-phase synchronous buck controller with on-chip drivers, remote output voltage sensing (VOUT2) and inductor DCR temperature compensation.
Demonstration circuit DC1441A is a dual output synchronous buck converter featuring the LTC3855EUJ. The board provides two outputs of 1.8V/17A and 1.2V/17A from an input voltage of 4.5V to 14V at a switching frequency of 400kHz.
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.
LTpowerCAD Project Files
Design tools for the following parts are available in LTpowerCAD:
Technical Articles (1)
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.
Sample & Buy
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 Analog Devices, Inc. sales office or authorized distributor. Pricing displayed for Evaluation Boards and Kits is based on 1-piece pricing.