SLVS543Q August   2004  – July 2022 TL431 , TL432


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Device Comparison Table
  6. Pin Configuration and Functions
  7. Specifications
    1. 7.1  Absolute Maximum Ratings
    2. 7.2  ESD Ratings
    3. 7.3  Thermal Information
    4. 7.4  Recommended Operating Conditions
    5. 7.5  Electrical Characteristics, TL431C, TL432C
    6. 7.6  Electrical Characteristics, TL431I, TL432I
    7. 7.7  Electrical Characteristics, TL431Q, TL432Q
    8. 7.8  Electrical Characteristics, TL431AC, TL432AC
    9. 7.9  Electrical Characteristics, TL431AI, TL432AI
    10. 7.10 Electrical Characteristics, TL431AQ, TL432AQ
    11. 7.11 Electrical Characteristics, TL431BC, TL432BC
    12. 7.12 Electrical Characteristics, TL431BI, TL432BI
    13. 7.13 Electrical Characteristics, TL431BQ, TL432BQ
    14.     Typical Characteristics
  8. Parameter Measurement Information
  9. Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
    4. 9.4 Device Functional Modes
      1. 9.4.1 Open Loop (Comparator)
      2. 9.4.2 Closed Loop
  10. 10Applications and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Applications
      1. 10.2.1 Comparator With Integrated Reference
        1. Design Requirements
        2. Detailed Design Procedure
          1. Basic Operation
            1. Overdrive
          2. Output Voltage and Logic Input Level
            1. Input Resistance
        3. Application Curve
      2. 10.2.2 Shunt Regulator/Reference
        1. Design Requirements
        2. Detailed Design Procedure
          1. Programming Output/Cathode Voltage
          2. Total Accuracy
          3. Stability
          4. Start-Up Time
        3. Application Curve
    3. 10.3 System Examples
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Device Nomenclature
    2. 13.2 Related Links
    3. 13.3 Receiving Notification of Documentation Updates
    4. 13.4 Support Resources
    5. 13.5 Trademarks
    6. 13.6 Electrostatic Discharge Caution
    7. 13.7 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

Package Options

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

Feature Description

TL43xx consists of an internal reference and amplifier that outputs a sink current base on the difference between the reference pin and the virtual internal pin. The sink current is produced by the internal Darlington pair, shown in the above schematic (Figure 9-2). A Darlington pair is used in order for this device to be able to sink a maximum current of 100 mA.

When operated with enough voltage headroom (≥ 2.5 V) and cathode current (IKA), TL431 forces the reference pin to 2.5 V. However, the reference pin can not be left floating, as it needs IREF ≥ 4 µA (please see Electrical Characteristics, TL431C, TL432C). This is because the reference pin is driven into an npn, which needs base current in order operate properly.

When feedback is applied from the Cathode and Reference pins, TL43xx behaves as a Zener diode, regulating to a constant voltage dependent on current being supplied into the cathode. This is due to the internal amplifier and reference entering the proper operating regions. The same amount of current needed in the above feedback situation must be applied to this device in open loop, servo or error amplifying implementations in order for it to be in the proper linear region giving TL43xx enough gain.

Unlike many linear regulators, TL43xx is internally compensated to be stable without an output capacitor between the cathode and anode. However, if it is desired to use an output capacitor Figure 9-2 can be used as a guide to assist in choosing the correct capacitor to maintain stability.