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

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8.5.1 Fault (ISET) and Current-Limit (ILIM) Thresholds

The ISET and ILIM thresholds is user programmable with a single external resistor connected to ISET and the ILIM threshold is internally set according to the ILIM/ISET ratio specified in the electrical characteristics table. The TPS2421 device uses an internal regulation loop to provide a regulated voltage on the ISET pin. The fault and current-limit thresholds are proportional to the current sourced out of ISET. The recommended 1% resistor range is 49.9 kΩ ≤ RRSET ≤ 200 kΩ to ensure the rated accuracy. Many applications require that minimum fault and current limits are known or that maximum current limit is bounded. Considering the tolerance of the fault and current limit thresholds, as well as RRSET when selecting values is important. See the Electrical Characteristics table for specific fault and current limit settings.

Using the data for ISET and ILIM from the Electrical Characteristics, equations are generated and used for other set points. Equation 8 and Equation 9 are used to calculate minimum and maximum ISET where RRSET,max and RRSET,min include RRSET tolerances. Equation 10 and Equation 11 calculate RRSET,max and RRSET,min where RTOL is the 1% resistor tolerance.

Equation 8. TPS2421-1 TPS2421-2 eq12_ISETmin_lus907.gif
Equation 9. TPS2421-1 TPS2421-2 eq13_ISETmax_lus907.gif
Equation 10. TPS2421-1 TPS2421-2 eq14_rsetmin_lus907.gif
Equation 11. TPS2421-1 TPS2421-2 eq15_RSETmax_lus907.gif

Equation 12 and Equation 13 are used to calculate minimum and maximum ILIM where RRSET,max and RRSET,min include RRSET tolerances.

Equation 12. TPS2421-1 TPS2421-2 eq16_ILIMmin_lus907.gif
Equation 13. TPS2421-1 TPS2421-2 eq17_ILIMmax_lus907.gif