2.7V to 5.5V Input, 4A Integrated MOSFET Single Synchronous Buck DC/DC Converter For Automotive

BD9S400MUF-C is a synchronous buck DC/DC Converter with built-in low On Resistance power MOSFETs. It is capable of providing current up to 4A. The SLLM™ control provides excellent efficiency characteristics in light-load conditions which make the product ideal for reducing standby power consumption of equipment. Small inductor is applicable due to high switching frequency of 2.2MHz. It is a current mode control DC/DC Converter and features high-speed transient response. Phase compensation can also be set easily. It can also be synchronized to external pulse.

8-channel power tree Reference Design
For automotive ADAS and Info-Display

Data Sheet Buy Sample
Data Sheet Buy Sample

Product Detail

Part Number | BD9S400MUF-CE2
Status | Recommended
Unit Quantity | 3000
Minimum Package Quantity | 3000
Packing Type | Taping
RoHS | Yes

Functional Safety:

Category : FS supportive
A product that has been developed for automotive use and is capable of supporting safety analysis with regard to the functional safety.




Common Standard

AEC-Q100 (Automotive Grade)



Integrated FET / Controller

Integrated FET



Synchronous / Nonsynchronous












SW frequency(Max.)[MHz]


Light Load mode






Operating Temperature (Min.)[°C]


Operating Temperature (Max.)[°C]


Package Size [mm]

3x3 (t=1)


  • SLLM™ (Simple Light Load Mode) Control
  • AEC-Q100 Qualified(Grade 1)
  • Single Synchronous Buck DC/DC Converter
  • Adjustable Soft Start Function
  • Power Good Output
  • Input Under Voltage Lockout Protection
  • Short Circuit Protection
  • Output Over Voltage Protection
  • Over Current Protection
  • Thermal Shutdown Protection
  • Wettable Flank QFN Package


    • Reference Design
    • REFRPT001-EVK-001
    • The REFRPT001-EVK-001 is a board included in power tree solution reference design named as REFRPT001 developed for infotainment devices such as vehicle clusters and center information displays, as well as for ADAS ECUs. The power system that can support functional safety is integrated on a single board, realizing an optimal configuration as a power tree.

  • User's Guide Detail

Design Resources



White Paper

  • Cutting-Edge Web Simulation Tool “ROHM Solution Simulator” Capable of Complete Circuit Verification of Power Devices and Driver ICs
  • For Automotive ADAS/Infotainment application, CISPR25 Class5 compliant 8 rails power tree Reference Design with power rail monitoring for supporting functional safety

User's Guide

  • User's Guide for REFRPT001-EVK-001

Reference Design

  • Application Note for REFRPT001-EVK-001
  • REFRPT001-EVK-001 EMC Test Report

Technical Articles

Schematic Design & Verification

  • Calculation of Power Dissipation in Switching Circuit
  • Considering Input Filter to Reduce Conducted Emissions by DCDC Converter
  • Considering Polarity of Power Inductor to Reduce Radiated Emission of DC-DC converter
  • Method for Monitoring Switching Waveform
  • Phase Compensation Design for Current Mode Buck Converter
  • Bootstrap Circuit in the Buck Converter
  • Method for Determining Constants of
  • Power Supply Sequence Circuit with General Purpose Power Supply IC
  • Suppression Method of Switching Noise Using Linear Regulator and Low Pass Filter
  • PCB Layout Techniques of Buck Converter
  • Measurement Method for Phase Margin with Frequency Response Analyzer (FRA)
  • Usage of SPICE Macromodel for DC/DC
  • Snubber Circuit for Buck Converter IC
  • Efficiency of Buck Converter
  • Calculation of Power Loss (Synchronous)
  • Inductor Calculation for Buck converter IC
  • Considerations for Power Inductors Used for Buck Converters
  • Capacitor Calculation for Buck converter IC
  • The Important Points of Multi-layer Ceramic Capacitor Used in Buck Converter circuit
  • Resistor Value Table to set Output Voltage of Buck Converter IC
  • Importance of Probe Calibration When Measuring Power: Deskew
  • Impedance Characteristics of Bypass Capacitor

Thermal Design

  • What Is Thermal Design
  • Basics of Thermal Resistance and Heat Dissipation
  • Method for Calculating Junction Temperature from Transient Thermal Resistance Data
  • Two-Resistor Model for Thermal Simulation
  • Notes for Temperature Measurement Using Thermocouples
  • Notes for Temperature Measurement Using Forward Voltage of PN Junction
  • Thermal Resistance
  • Precautions When Measuring the Rear of the Package with a Thermocouple


Simulations (Login Required)

ROHM Solution Simulator is a new web-based electronic circuit simulation tool that can carry out a variety of simulations, from initial development that involves component selection and individual device verification to the system-level verification stage. This makes it possible to quickly and easily implement complete circuit verification of ROHM power devices and ICs, in simulation circuits under close to actual conditions, significantly reducing application development efforts.
  • BD9S400MUF / Frequency Domain
  • REFRPT001 / Load Response for 3.3V Power Tree Sub-circuit
  • Simulation Guide for REFRPT001 for 3.3V power tree sub-circuit / Load Response (ROHM Solution Simulator)


  • Unencrypted SPICE Model (Inquiry Form)
  • BD9S400MUF-C SPICE Model
  • BD9S400MUF-C SPICE Modeling Report
  • BD9S400MUF-C Two-Resistor Thermal Model Report


  • BD9S400MUF-C Footprint / Symbol
  • VQFN16FV3030 Footprint / Symbol
  • VQFN16FV3030 3D STEP Data

Packaging & Quality

Package Information

  • Package Information

Manufacturing Data

  • Factory Information

Environmental Data

  • REACH SVHC Non-use Declaration