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LM21305

ACTIVE

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

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TPS566242 ACTIVE 3-V to 16-V input voltage, 6-A ECO mode, synchronous buck converter in SOT-563 package Higher efficiency with lower IQ and more features in a smaller package.

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 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 Control mode current mode Duty cycle (max) (%) 100 Type Converter
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 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 Control mode current mode Duty cycle (max) (%) 100 Type Converter
WQFN (RSG) 28 25 mm² 5 x 5
  • 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
  • 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

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).

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
* Data sheet LM21305 3-V to 18-V, 5-A, Adjustable Frequency Synchronous Buck Converter datasheet (Rev. G) PDF | HTML 25 Sep 2015
User guide LM21305 Step-Down Converter Evaluation Module User's Guide (Rev. D) PDF | HTML 11 Jan 2022
Selection guide Buck Converter Quick Reference Guide (Rev. B) 08 Apr 2021
Selection guide Power Management Guide 2018 (Rev. R) 25 Jun 2018
User guide AN-2175 LM21305 POL Demonstration Module and Reference Design (Rev. B) 05 May 2013

Design & development

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

Evaluation board

LM21305EVM — LM21305 Evaluation Board

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 (...)

User guide: PDF | HTML
Not available on TI.com
Simulation model

LM21305 PSpice Transient Model (Rev. A)

SNVM705A.ZIP (292 KB) - PSpice Model
Simulation model

LM21305 SIMPLIS Transient and Average Model (Rev. B)

SNVMCA1B.ZIP (2394 KB) - SIMPLIS Model
Calculation tool

LM21305-QUICKSTART-CALC — LM21305 QuickStart Calculator

Simulation tool

PSPICE-FOR-TI — PSpice® for TI design and simulation tool

PSpice® for TI is a design and simulation environment that helps evaluate functionality of analog circuits. This full-featured, design and simulation suite uses an analog analysis engine from Cadence®. Available at no cost, PSpice for TI includes one of the largest model libraries in the (...)
Reference designs

PMP7877 — Power Reference Design for Xilinx® Zynq®-7000

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 (...)
Test report: PDF
Schematic: PDF
Package Pins Download
WQFN (RSG) 28 View options

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