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).
| 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 |
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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 (...)
| Package | Pins | CAD symbols, footprints & 3D models |
|---|---|---|
| WQFN (RSG) | 28 | Ultra Librarian |
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