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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8.4.1 Startup

Large inrush current occurs when power is applied to discharged capacitors and load. During the inrush period, the TPS2421 device operates in power limit (or SOA protect mode) managing the current as VVOUT rises. In SOA protect mode, the internal MOSFET power dissipation ([VVIN – VVOUT] × IVOUT) is regulated at 5 W typical while the fault timer starts and CCT ramps up. As the charge builds on CLOAD, the current increases towards ILIM. When the capacitor is fully charged, IVOUT drops to the dc load value, the fault timer stops, and CCT ramps down. In order for the TPS2421 device to start properly, the fault timer duration must exceed CLOAD startup time, tON. Startup time without additional dc loading is calculated using Equation 5 where PLIM = 5 W (typical).

Equation 5. TPS2421-1 TPS2421-2 Eq5_tON_lus907.gif

When the load has a resistive component in addition to CLOAD, the fault time must be extended because the resistive load current is unavailable to charge CLOAD. Use Table 1 and Table 2 to predict startup time in the presence of resistive dc loading.

Refer to the TPS2421 Design Calculator Tool (SLUC427) for assistance with design calculations.

Table 1. Startup Time (ms) with DC Loading: VIN = 5 V, PLIM = 3 W, ILIM = 5 A

RLOAD_(Ω) CLOAD_ = 100 µF CLOAD_ = 220 µF CLOAD_ = 470 µF CLOAD_ = 1000 µF
1000 0.43 0.95 2.03 4.33
10 0.5 1.11 2.36 5.03
5 0.61 1.34 2.87 6.1
3 0.91 2 4.28 9.11
2.5 1.31 2.88 6.14 13.07

Table 2. Startup Time (ms) with DC Loading: VIN = 12 V, PLIM = 3 W, ILIM = 5 A

RLOAD_(Ω) CLOAD_ = 100 µF CLOAD_ = 220 µF CLOAD_ = 470 µF CLOAD_ = 1000 µF
10000 2.46 5.41 11.56 24.59
100 2.67 5.87 12.55 26.69
50 2.93 6.45 13.79 29.34
15 6.7 14.74 31.5 67.01
13 11.68 25.69 54.87 116.75