Wide Input 4.5-V to 100-V, 1-A Synchronous Buck / Fly-Buck Converter


Product details


Vin (Min) (V) 4.5 Vin (Max) (V) 100 Vout (Min) (V) 2 Vout (Max) (V) 92 Switching frequency (Max) (kHz) 1000 Soft start Adjustable Features Enable, Light Load Efficiency, Pre-Bias Start-Up, Synchronous Rectification Operating temperature range (C) -40 to 125 Iout (A) 1 Topology Buck Product type Converter (Integrated switch) open-in-new Find other Flybuck converters

Package | Pins | Size

HTSSOP (PWP) 14 32 mm² 5 x 6.4 open-in-new Find other Flybuck converters


  • Wide 4.5-V to 100-V Input Voltage Range
  • Integrated High-Side and Low-Side Switches
    • No Schottky Diode Required
  • 1-A Maximum Load Current
  • Constant ON-Time Control
    • No External Loop Compensation
    • Fast Transient Response
  • Selectable DCM Buck Operation at Light Load
  • CCM Option Supports Multi-Output Fly-Buck™
  • No External Ripple circuit needed (at FPWM = 0)
  • Nearly Constant Switching Frequency
  • Frequency Adjustable Up to 1 MHz
  • Programmable Soft-Start Time
  • Prebias Start-Up
  • Peak Current Limiting Protection
  • Adjustable Input UVLO and Hysteresis
  • ±1% Feedback Voltage Reference
  • Thermal Shutdown Protection
  • Create a Custom Design Using the LM5161 With the WEBENCH® Power Designer
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The LM5161 is a 100-V, 1-A synchronous step-down converter with integrated high-side and low-side MOSFETs. The constant-ON-time control scheme requires no loop compensation and supports high step-down ratios with fast transient response. An internal feedback amplifier maintains ±1% output voltage regulation over the entire operating temperature range. The ON-time varies inversely with input voltage resulting in nearly constant switching frequency. Peak and valley current limit circuits protect against overload conditions. The under-voltage lockout (EN/UVLO) circuit provides independently adjustable input undervoltage threshold and hysteresis. The FPWM input pin in LM5161 selects either the forced continuous conduction mode (CCM) under all load levels or the discontinuous conduction mode (DCM) under light or no load conditions. When operating in forced CCM, the LM5161 supports the multiple output and isolated Fly-Buck applications. When programmed for the DCM operation, the LM5161 provides a tightly regulated buck output without any additional external feedback ripple injection circuit.

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Technical documentation

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Type Title Date
* Data sheet LM5161 Wide Input 100-V, 1-A Synchronous Buck/Fly-Buck™ Converter datasheet (Rev. B) Nov. 27, 2017
Application note Step-Dwn (Buck) Convrtr Pwer Solutions for Programmable Logic Controller Systems (Rev. A) Jul. 26, 2021
Selection guide Buck Converter Quick Reference Guide (Rev. B) Apr. 08, 2021
White paper Valuing wide VIN, low EMI synchronous buck circuits for cost-driven, demanding a (Rev. A) Apr. 10, 2019
Application note Stability Analysis and Design of COT Type-3 Ripple Circuit Mar. 20, 2019
Application note Powering Drones With a Wide VIN DC-DC Converter (Rev. A) Feb. 05, 2019
Technical article Why a wide VIN DC/DC converter is a good fit for high-cell-count battery-powered drones Nov. 21, 2017
Technical article Simplifying 100V wide VIN power conversion Nov. 11, 2016
User guide LM5161 Fly-Buck (Isolated Buck) EVM User’s Guide (Rev. A) Aug. 19, 2016
User guide LM5161PWPBKEVM Buck Evaluation Module User's Guide (Rev. A) Aug. 19, 2016
Technical article Create a Fly-Buck™ converter in WEBENCH® Power Designer Oct. 09, 2015
White paper Designing isolated rails on the fly with Fly-Buck™ converters Sep. 29, 2015
Technical article How to design for EMC and isolation with Fly-Buck™ converters Jul. 28, 2015
Application note Is Your IGBT Gate-Driver Power Supply Optimized Mar. 12, 2015
Application note Fly-Buck(TM) converter provides EMC and isolation in PLC applications Jan. 29, 2015
Application note AN-2292 Designing an Isolated Buck (Fly-Buck) Converter (Rev. C) Dec. 17, 2014
White paper Wide VIN power management ICs simplify white paper (Rev. A) Sep. 19, 2013
Application note AN-2218 Precision Current Limiting with the LMP8646 and LM3102 (Rev. A) Apr. 23, 2013

Design & development

For additional terms or required resources, click any title below to view the detail page where available.

Hardware development

document-generic User guide
The LM5161PWPBKEVM evaluation board provides a fully functional buck regulator, employing the constant on-time (COT) operating principle. This evaluation board provides a 12-V output over an input range of 15V to 80 V. The circuit delivers load currents to 1.0 A. The application schematic is setup (...)
  • 15V to 80V input voltage range
  • 12V target output voltage
  • Delivers up to 1.0A output load current
  • FPWM mode pin feature to choose between CCM and DCM
document-generic User guide
The LM5161PWPFBKEVM evaluation board provides a fully functional Fly-buck regulator, employing the constant on-time (COT) operating principle. This evaluation board provides a 12-V secondary isolated output voltage over an input range of 36V to 72 V. The circuit delivers secondary output load (...)
  • 36V to 72V input voltage range
  • 12V target secondary isolated output voltage
  • Delivers up to 800mA secondary output load current

Design tools & simulation

SNVMAV3.ZIP (499 KB) - PSpice Model
SNVMAV4.ZIP (3 KB) - PSpice Model
Fly-Buck and Flyback Topology Selector
FLYBUCK-FLYBACK-DESIGN-CALC This tool helps a power supply engineer to select the right isolated DC-DC topology based on the specifications. Depending on the topology chosen, the calculator also recommends the right IC for the design.
  • Features isolated topologies like Fly-Buck™, Fly-Buck-Boost, DCM and CCM Flyback
  • Capability to design up to 6 isolated outputs
  • Recommends ICs for desired application design
  • Incorporates loop compensation in designs
  • Compares efficiency, external component count and transformer currents for every topology (...)
SNVC199.ZIP (383 KB)
SNVC200.ZIP (287 KB)

Reference designs

Inverting buck-boost reference design
PMP20587 — This reference design uses UCD3138064A as a digital controller to control two-phase two-rail inverting buck-boost. This non-isolated converter is used for wireless radio power. The input voltage is from -35 V to -60 V. There are two outputs. The default output voltage of rail 1 is 32 V and max (...)
document-generic Schematic document-generic User guide
48Vin Digital POL with 3 Outputs Reference Design
PMP4486 — The PMP4486 is a GaN-based reference design solution for telecom and computing applications. The GaN module LMG5200 enables a high efficiency single stage conversion with an input range from 36 to 60V down to 29V, 12V and 1.0V. This design shows the benefits of a GaN based design with high (...)
document-generic Schematic document-generic User guide
Flybuck For 48Vin Isolated System Aux. Power Reference Design
PMP40042 — The PMP40042 is a D-CAP Aux. isolated power supply reference design solution for the Telecom & Server applications. High integration and low switching loss, with the UVLO, OTP, OCP, SS and Prebias Start-up, the module enables a high efficiency for 48V system application.  A low cost & (...)
document-generic Schematic document-generic User guide

CAD/CAE symbols

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