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

9.2 AVIN Filter

This can be seen on the schematic as components RF and CF. There is a practical limit to the size of the resistor RF as the AVIN pin will draw a short 60-mA burst of current during start-up, and if RF is too large the resulting voltage drop can trigger the UVLO comparator. For the evaluation board, a 1-Ω resistor is used for RF ensuring that the UVLO will not be triggered after the part is enabled. A recommended 1-μF CF capacitor coupled with the 1-Ω resistor provides approximately 10 dB of attenuation at 500-kHz switching frequency.