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

8.3.1 CT

Connect a capacitor from CT to GND to set the fault time. The fault timer starts when IVOUT exceeds ISET or when SOA protection mode is active, charging the capacitor with 35 μA from GND towards an upper threshold of 1.4 V. If the capacitor reaches the upper threshold, the internal pass MOSFET is turned off. For the TPS2421-1 device, the MOSFET remains off until EN is cycled. For the TPS2421-2 device, the capacitor discharges at 1.4 μA to 0.16 V and then re-enable the pass MOSFET. If the upper threshold is not crossed, the capacitor discharges at 40 μA to 0.16 V and then to 0 V at 1.4 μA. When the device is disabled, CT is pulled to GND through a 50-kΩ resistor.

The timer period must be chosen long enough to allow the external load capacitance to charge. The nominal (not including component tolerances) fault timer period is selected using Equation 1 where TFAULT is the minimum timer period in seconds and CCT is in Farads.

Equation 1. TPS2421-1 TPS2421-2 qu1_lus907.gif

For the TPS2421-2 device, the second and subsequent retry timer periods are slightly shorter than the first retry period. CT nominal (not including component tolerances) discharge time, tSD from 1.4 V to 0.16 V is shown in Equation 2, where CCT is in Farads and tSD is in seconds.

Equation 2. TPS2421-1 TPS2421-2 qu2_lus907.gif

The nominal ratio of on to off times represents about a 3.7% duty cycle when a hard fault is present on the output.