SLVSDT3D January   2018  – December 2019 TPS25221

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
  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 Parameter Measurement Information
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Over-current Conditions
      2. 9.3.2 Fault Response
      3. 9.3.3 Undervoltage Lockout (UVLO)
      4. 9.3.4 Enable, (EN)
      5. 9.3.5 Thermal Sense
    4. 9.4 Device Functional Modes
    5. 9.5 Programming
      1. 9.5.1 Programming the Current-Limit Threshold
  10. 10Application and Implementation
    1. 10.1 Application Information
      1. 10.1.1 Constant-Current
    2. 10.2 Typical Applications
      1. 10.2.1 Two-Level Current-Limit Circuit
        1. 10.2.1.1 Design Requirements
        2. 10.2.1.2 Detailed Design Procedures
          1. 10.2.1.2.1 Designing Above a Minimum Current Limit
          2. 10.2.1.2.2 Designing Below a Maximum Current Limit
          3. 10.2.1.2.3 Accounting for Resistor Tolerance
          4. 10.2.1.2.4 Input and Output Capacitance
        3. 10.2.1.3 Application Curve
      2. 10.2.2 Auto-Retry Functionality
        1. 10.2.2.1 Design Requirements (added)
        2. 10.2.2.2 Detailed Design Procedure
      3. 10.2.3 Typical Application as USB Power Switch
        1. 10.2.3.1 Design Requirements
          1. 10.2.3.1.1 USB Power-Distribution Requirements
        2. 10.2.3.2 Detailed Design Procedure
          1. 10.2.3.2.1 Universal Serial Bus (USB) Power-Distribution Requirements
  11. 11Power Supply Recommendations
    1. 11.1 Self-Powered and Bus-Powered Hubs
    2. 11.2 Low-Power Bus-Powered and High-Power Bus-Powered Functions
    3. 11.3 Power Dissipation and Junction Temperature
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Support
      1. 13.1.1 Third-Party Products Disclaimer
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Community Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

10.2.1.2.3 Accounting for Resistor Tolerance

The previous sections described the selection of RILIM given certain application requirements and the importance of understanding the current-limit threshold tolerance. The analysis focused only on TPS25221 performance and assumed an exact resistor value. However, resistors sold in quantity are not exact and are bounded by an upper and lower tolerance centered around a nominal resistance. The additional RILIM resistance tolerance directly affects the current-limit threshold accuracy at a system level. The following table shows a process that accounts for worst-case resistor tolerance assuming 1% resistor values. Step one follows the selection process outlined in the application examples above. Step two determines the upper and lower resistance bounds of the selected resistor. Step three uses the upper and lower resistor bounds in the IOS equations to calculate the threshold limits. It is important to use tighter tolerance resistors, for example, 0.5% or 0.1%, when precision current limiting is desired.

Table 3. Common RILIM Resistor Selections

DESIRED
NOMINAL
CURRENT LIMIT
(mA) 		IDEAL
RESISTOR
(kΩ) 		CLOSEST
1% RESISTOR
(kΩ) 		RESISTOR TOLERANCE ACTUAL LIMITS
1% LOW (kΩ) 1% HIGH (kΩ) IOS(min) (mA) IOS(nom) (mA) IOS(max) (mA)
275 199.2 200 198 202 236 274 312
400 137.2 137 135.6 138.4 349 401 450
500 109.8 110 108.9 111.1 438 499 556
600 91.6 90.9 90.0 91.8 533 605 669
700 78.6 78.7 77.9 79.5 619 699 770
800 68.8 68.1 67.4 68.8 719 808 886
900 61.2 61.9 61.3 62.5 793 889 972
1000 55.1 54.9 54.4 55.4 898 1003 1092
1200 45.9 46.4 45.9 46.9 1068 1188 1285
1400 39.4 39.2 38.8 39.6 1272 1407 1514
1600 34.5 34.8 34.5 35.1 1438 1585 1699
1800 30.7 30.9 30.6 31.2 1626 1786 1907
2000 27.6 27.4 27.1 27.7 1841 2015 2143
2200 25.1 24.9 24.7 25.1 2032 2219 2351
2400 23.0 23.2 23.0 23.4 2186 2382 2518
2600 21.3 21.5 21.3 21.7 2365 2571 2711
2700 20.5 20.5 20.3 20.7 2484 2697 2839