3-18V, 5A, Current Mode Synchronous Buck Regulator with Adjustable Frequency


Product details


Vin (Min) (V) 3 Vin (Max) (V) 18 Vout (Min) (V) 0.6 Vout (Max) (V) 0.6 Iout (Max) (A) 5 Iq (Typ) (mA) 9 Iq (Typ) (uA) 9000 Switching frequency (Min) (kHz) 300 Switching frequency (Max) (kHz) 1500 Features Enable, Frequency Synchronization, Power Good, Pre-Bias Start-Up, Synchronous Rectification Operating temperature range (C) -40 to 85 Rating Catalog Regulated outputs (#) 1 open-in-new Find other Buck converters (integrated switch)

Package | Pins | Size

WQFN (RSG) 28 25 mm² 5 x 5 open-in-new Find other Buck converters (integrated switch)


  • High-Efficiency Synchronous DC-DC Converter:
    • Integrated Low RDSon Power MOSFETs
    • Wide Input Voltage Range: 3 V to 18 V
    • Load Current as High as 5 A
    • Switching Frequency: 300 kHz to 1.5 MHz
  • External Frequency Synchronization
  • Accurate 0.598-V Feedback Voltage Reference
  • Ultra-Fast Line and Load Transient Response:
    • Peak Current-Mode Control
    • Internal Slope Compensation
    • High-Bandwidth Error Amplifier
  • Ultra-Low Shutdown Quiescent Current
  • Wide Duty-Cycle Operating Range:
    • TON-MIN: 70 ns for Low VOUT
    • TOFF-MIN: 50 ns for High Duty Cycle
  • Diode Emulation Mode at Light Loads
  • Integrated Bias Supply LDO Sub-Regulators
  • Internal Soft-Start Function:
    • Monotonic Startup into Pre-Biased Loads
  • Precision Enable Input with Hysteresis
  • Open-Drain PGOOD Indicator
  • Internal Input Undervoltage Lockout (UVLO)
  • Cycle-by-Cycle Overcurrent Protection
  • Output Overvoltage Protection (OVP)
  • Thermal Shutdown Protection with Hysteresis
  • 5-mm × 5-mm WQFN-28 PowerPAD™ Package
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The LM21305 is a full-featured, 5-A, synchronous buck dc-dc converter optimized for solution size, flexibility, and high conversion efficiency. High-power density LM21305 designs are easily achieved by virtue of monolithic integration of high-side and low-side power MOSFETs, high switching frequency, peak current-mode control, and optimized thermal design. The efficiency of the LM21305 is maximized at light loads with diode emulation mode operation and at heavy loads by optimal design of the MOSFET adaptive gate drivers to minimize switch dead-times and body-diode conduction losses.

The LM21305 accepts a wide input voltage range of 3 V to 18 V for interface to various intermediate bus voltages, including 3.3-V, 5-V, and 12-V rails. A 1.5% voltage reference and 70-ns, high-side MOSFET minimum controllable on-time enable output voltages as low as 0.598 V with excellent setpoint accuracy. The LM21305 is available in a 5-mm × 5-mm2 WQFN-28 thermally-enhanced package with 0.5-mm pitch.

The LM21305 offers flexible system configuration with programmable switching frequency from 300 kHz to 1.5 MHz using one resistor or by external clock synchronization for beat-frequency-sensitive and multi-regulator applications. On-chip bias supply low-dropout (LDO) sub-regulators eliminate the need for an external bias power and simplify circuit board layout. The device also offers an internal soft-start to limit inrush current and provide monotonic startup capability into unbiased and pre-biased loads, integrated boot diodes, cycle-by-cycle current limiting, and thermal shutdown. Peak current-mode control with a high-gain error amplifier maintains stability throughout the entire input voltage and load current ranges, enabling excellent line and load transient response.

The LM21305 features internal output overvoltage protection (OVP) and overcurrent protection (OCP) circuits for increased system reliability. An integrated open-drain, PGOOD indicator provides output voltage monitoring, power-rail sequencing capability, and fault indication. Other features include thermal shutdown with automatic recovery, low PWM minimum on-time, low shutdown quiescent current, and precision enable with hysteresis for programmable line undervoltage lockout (UVLO).

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Technical documentation

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Type Title Date
* Datasheet LM21305 3-V to 18-V, 5-A, Adjustable Frequency Synchronous Buck Converter datasheet (Rev. G) Sep. 25, 2015
Selection guides Buck Converter Quick Reference Guide (Rev. A) Mar. 31, 2020
Technical articles Minimize the impact of the MLCC shortage on your power application Mar. 29, 2019
Selection guides Power Management Guide 2018 (Rev. R) Jun. 25, 2018
Technical articles Exploiting current-mode control for wide Vin DC/DC conversion Aug. 14, 2014
User guides AN-2042 LM21305 Evaluation Board (Rev. C) May 05, 2013
User guides AN-2175 LM21305 POL Demonstration Module and Reference Design (Rev. B) May 05, 2013
Technical articles Introducing TI’s new Power Solution Video Series Apr. 19, 2012

Design & development

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Hardware development

document-generic User guide

The LM21305 is a full-featured adjustable frequency synchronous buck point-of-load regulator capable of delivering up to 5A of continuous output current. The device is optimized to work over an input voltage range of 3V to 18V and an output voltage range of 0.6V to 5V, making it suitable for wide (...)



  • LM21305 evaluation board

Design tools & simulation

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LM21305 QuickStart Calculator

Reference designs

Power Reference Design for Xilinx® Zynq®-7000
PMP7877 The PMP7877 reference design provides all the rails necessary to power a Xilinx® Zynq®-7000 series SoC.  It operates from an input voltage range of 10.8Vin to 13.2Vin and has seven regulated outputs: 1Vout @ 5A, 1.8Vout @ 2.5A, 1.5Vout @ 6A, 3.3Vout @ 5A, 3.3Vout @ 5A, 5Vout @ 2A, and (...)
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WQFN (RSG) 28 View options

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