SNVA432D March   2010  – January 2022 LM21305

 

  1.   Trademarks
  2. 1 LM21305 Overview
  3. 2 Typical Application Circuit
  4. 3 Evaluation Board Schematic
  5. 4 Evaluation Board Bill of Materials (BOM)
  6. 5 Connection Descriptions
  7. 6 Jumper Settings
  8. 7 Other Design Examples
  9. 8 Typical Performance Characteristics
  10. 9 Component Selection
    1. 9.1 Input Capacitors
    2. 9.2 AVIN Filter
    3. 9.3 Switching Frequency Selection
    4. 9.4 Inductor
    5. 9.5 Output Capacitor
    6. 9.6 Compensation Circuit
  11. 10PCB Layout
  12. 11Revision History

1 LM21305 Overview

The LM21305 is a full-featured adjustable frequency synchronous buck point-of-load regulator capable of delivering up to 5 A of continuous output current. The device is optimized to work over an input voltage range of 3 V to 18 V and an output voltage range of 0.598 V to 5 V, making it suitable for wide variety of applications. The LM21305 provides excellent output voltage accuracy and superior line and load transient response for digital loads. The device offers flexible system configuration through programmable switching frequency through an external resistor with ability to synchronize the switching frequency to an external clock. The frequency can be set from 300 kHz to 1.5 MHz. The device also provides the following:

  • Internal soft start to limit in-rush current
  • Pre-biased and monotonic start up capability
  • Cycle-by-cycle current limiting
  • Thermal shutdown

The device features internal overvoltage protection (OVP) and overcurrent protection (OCP) circuits for increased system reliability. A precision enable pin and integrated undervoltage lockout (UVLO) allows the turn-on of the device to be tightly controlled and sequenced. Fault detection and supply sequencing are possible with the integrated power good circuit.

The LM21305 is offered in a WQFN-28 package with an exposed pad for enhanced thermal performance. The LM21305 evaluation board comes ready to operate at the following conditions:

Parameter Default Range and Options
PVIN 12 V External supply 5 V to 18 V
AVIN =PVIN Connect to PVIN or to separate supply (3 V to 18 V) selected by JP1
VOUT 3.3 V 0.598 V to 5 V by changing R5, R6, or both
Switching frequency 500 kHz 300 kHz to 1.5 MHz by changing R4
IOUT 0 A to 5 A
Size 2 inches × 1.5 inches
Number of PCB layers 4