ZHCSC61B March   2014  – September 2020 TPS2556-Q1 , TPS2557-Q1

PRODUCTION DATA  

  1. 1 特性
  2. 2 应用
  3. 3 说明
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Terminal Configuration and Functions
    1.     Terminal Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 Handling Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Switching Characteristics
    7. 7.7 Typical Characteristics
      1.      16
  8. 8 Parameter Measurement Information
    1.     18
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Overcurrent Conditions
      2. 9.3.2 FAULT Response
      3. 9.3.3 Thermal Sense
    4. 9.4 Device Functional Modes
      1. 9.4.1 Undervoltage Lockout (UVLO)
      2. 9.4.2 Enable ( EN OR EN)
      3. 9.4.3 Auto-Retry Functionality
      4. 9.4.4 Two-Level Current-Limit Circuit
  10. 10Applications and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application, Design for Current Limit
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Determine Design Parameters
        2. 10.2.2.2 Programming the Current-Limit Threshold
        3. 10.2.2.3 Selecting Current-Limit Resistor 1
        4. 10.2.2.4 Selecting Current-Limit Resistor 2
        5. 10.2.2.5 Accounting for Resistor Tolerance
        6. 10.2.2.6 Power Dissipation and Junction Temperature
      3. 10.2.3 Application Curves
  11. 11Power Supply Recommendations
    1.     44
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Related Links
    2. 13.2 Trademarks
    3. 13.3 Electrostatic Discharge Caution
    4. 13.4 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

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10.2.2.5 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 the TPS2556-Q1 and TPS2557-Q1 device 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 foregoing application examples. 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 desirable.

Table 10-2 Common RILIM Resistor Selections
Desired Nominal Current Limit (mA)Ideal Resistor (kΩ)Closest 1% Resistor (kΩ)Resistor ToleranceActual Limits
1% low (kΩ)1% high (kΩ)IOS MIN (mA)IOS NOM (mA)IOS MAX (mA)
750148.1147145.5148.5632756881
1000111.3110108.9111.185910111161
125089.188.787.889.6107912561426
150074.37574.375.8128914861673
175063.763.462.864.0154017601964
200055.856.255.656.8174919862203
225049.649.949.450.4198322382468
250044.744.243.844.6225525282770
275040.740.239.840.6249327813033
300037.337.437.037.8269129913249
325034.434.834.535.1290432153480
350032.031.631.331.9321635423816
375029.930.129.830.4338637203997
400028.02827.728.3365540004282
425026.426.125.826.4393742934579
450024.924.924.725.1413845014789
475023.623.723.523.9436047305020
500022.422.622.422.8458549615253
525021.421.521.321.7483452165509
550020.420.520.320.7508354725765