SLUS907K January   2009  – June 2019 TPS2421-1 , TPS2421-2

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 CT
      2. 8.3.2 FLT
      3. 8.3.3 GND
      4. 8.3.4 ISET
      5. 8.3.5 VIN
      6. 8.3.6 VOUT
      7. 8.3.7 PG
    4. 8.4 Device Functional Modes
      1. 8.4.1 Startup
      2. 8.4.2 Maximum Allowable Load to Ensure Successful Startup
        1. 8.4.2.1 Enable Pin Considerations
        2. 8.4.2.2 Fault Timer
        3. 8.4.2.3 Normal Operation
        4. 8.4.2.4 Startup into a Short
      3. 8.4.3 Shutdown Modes
        1. 8.4.3.1 Hard Overload - Fast Trip
        2. 8.4.3.2 Overcurrent Shutdown
    5. 8.5 Programming
      1. 8.5.1 Fault (ISET) and Current-Limit (ILIM) Thresholds
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Transient Protection
      3. 9.2.3 Application Curves
  10. 10Power Supply Recommendations
    1. 10.1 PowerPad™
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Related Links
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Community Resource
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

8.4.2 Maximum Allowable Load to Ensure Successful Startup

The power limiting function of the TPS2421 provides effective protection and limits the maximum allowable resistive load (RMIN) during startup to ensure SOA of the device. Load resistance lower than RMIN can cause the output to shut off due to CT timeout or thermal shutdown. The equation for maximum load RMIN as a function of VIN, PLIM and ILIM is given by Equation 6:

Equation 6. TPS2421-1 TPS2421-2 Equation_Max_Load.gif

where

  • K = 0.15 for RRSET = 200 kΩ
  • K = 0.3 for RRSET = 100 kΩ
  • K = 0.5 for RRSET = 49.9 kΩ
  • ILIM(min) is the current limit minimum specification given in the EC Table

The device fails to start if RLOAD < RMIN. It either enters thermal shutdown or CT timer may timeout. The load resistance during startup (RLOAD) must be higher than RMIN for a successful startup. Ensure that RLOAD is > RMIN per Equation 6.