SLVS503F November   2003  – February 2020 TPS2490 , TPS2491

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Switching Characteristics
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  VCC
      2. 7.3.2  SENSE
      3. 7.3.3  GATE
      4. 7.3.4  OUT
      5. 7.3.5  EN
      6. 7.3.6  VREF
      7. 7.3.7  PROG
      8. 7.3.8  TIMER
      9. 7.3.9  PG
      10. 7.3.10 GND
    4. 7.4 Device Functional Modes
      1. 7.4.1 Board Plug-In ()
      2. 7.4.2 TIMER and PG Operation ()
      3. 7.4.3 Action of the Constant Power Engine ()
      4. 7.4.4 Response to a Hard Output Short ( and )
      5. 7.4.5 Automatic Restart ()
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Alternative Inrush Designs
        1. 8.1.1.1 Gate Capacitor (dV/dt) Control
        2. 8.1.1.2 PROG Inrush Control
      2. 8.1.2 Additional Design Considerations
        1. 8.1.2.1 Use of PG
        2. 8.1.2.2 Faults and Backplane Voltage Droop
        3. 8.1.2.3 Output Clamp Diode
        4. 8.1.2.4 Gate Clamp Diode
        5. 8.1.2.5 High Gate Capacitance Applications
        6. 8.1.2.6 Input Bypass
        7. 8.1.2.7 Output Short Circuit Measurements
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Select RSNS and CL setting
        2. 8.2.2.2 Selecting the Hot Swap FET(s)
        3. 8.2.2.3 Select Power Limit
        4. 8.2.2.4 Set Fault Timer
        5. 8.2.2.5 Check MOSFET SOA
        6. 8.2.2.6 Set Under-Voltage Threshold
        7. 8.2.2.7 Choose R5, and CIN
        8. 8.2.2.8 Input and Output Protection
        9. 8.2.2.9 Final Schematic and Component Values
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 PC Board Guidelines
      2. 10.1.2 System Considerations
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Development Support
    2. 11.2 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Related Links
    4. 11.4 Receiving Notification of Documentation Updates
    5. 11.5 Community Resources
    6. 11.6 Trademarks
    7. 11.7 Electrostatic Discharge Caution
    8. 11.8 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Refer to the PDF data sheet for device specific package drawings

Mechanical Data (Package|Pins)
  • DGS|10
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2.2 Selecting the Hot Swap FET(s)

It is critical to select the correct MOSFET for a hot swap design. The device must meet the following requirements:

  • The VDS rating should be sufficient to handle the maximum system voltage along with any ringing caused by transients. For most 12-V systems a 30-V FET is a good choice.
  • The SOA of the FET should be sufficient to handle all usage cases: start-up, hot-short, start into short.
  • RDSON should be sufficiently low to maintain the junction and case temperature below the maximum rating of the FET. TI recommends to keep the steady state FET temperature below 125°C to allow margin to handle transients.
  • Maximum continuous current rating should be above the maximum load current and the pulsed drain current must be greater than the current threshold of the circuit breaker. Most MOSFETs that pass the first three requirements also pass these two.
  • A VGS rating of ±20 V is required, because the TPS2490 can pull up the gate as high as 16 V above source.

For this design the CSD19532KTT was selected for its low RDSON and good SOA. After selecting the MOSFET, the maximum steady state case temperature can be computed as follows:

Equation 9. TPS2490 TPS2491 tps2490_equation4.gif

Note that the RDSON is a strong function of junction temperature, which for most MOSFETs will be close to the case temperature. A few iterations of the above equations may be necessary to converge on the final RDSON and TC,MAX value. According to the CSD17552Q5B datasheet, its RDSON is approximately 1.4x at 78°C. The Equation 10 uses this RDSON value to compute the TC,MAX.

Equation 10. TPS2490 TPS2491 tps2490_equation5.gif

This maximum steady state case temperature indicates that a second MOSFET is not needed to reduce and distribute power dissipation during normal operation.

For reference, when using parallel MOSFETs, the maximum steady state case temperature can be computed as follows:

Equation 11. TPS2490 TPS2491 tps2490_equation6.gif

Iterate until the computed TC,MAX is using two parallel MOSFETs is less than to the junction temperature assumed for RDSON. Then, no further iterations are necessary.