SLVS062N December   1991  – October 2016 TL1431 , TL1431M

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings - TL1431C, TL1431Q
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics - TL1431C
    6. 6.6 Electrical Characteristics - TL1431Q
    7. 6.7 Electrical Characteristics - TL1431M
    8. 6.8 Typical Characteristics
  7. 7 Parameter Measurement Information
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
    4. 8.4 Device Functional Modes
      1. 8.4.1 Open Loop (Comparator)
      2. 8.4.2 Closed Loop
  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 Programming Output/Cathode Voltage
        2. 9.2.2.2 Total Accuracy
        3. 9.2.2.3 Stability
        4. 9.2.2.4 Start-up Time
      3. 9.2.3 Application Curve
    3. 9.3 System Examples
  10. 10Power Supply Recommendations
  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 Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component specification, and TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining suitability of components for their purposes. Customers should validate and test their design implementation to confirm system functionality.

9.1 Application Information

As the TL1431 device has many applications and setups, there are many situations that this datasheet cannot characterize in detail. The linked application notes help the designer make the best choices when using this part. Understanding Stability Boundary Conditions Charts in TL431, TL432 Data Sheet (SLVA482) provides a deeper understanding of this devices stability characteristics and aid the user in making the right choices when choosing a load capacitor. Setting the Shunt Voltage on an Adjustable Shunt Regulator (SLVA445) assists designers in setting the shunt voltage to achieve optimum accuracy for this device.

9.2 Typical Application

TL1431 TL1431M SHUNT_APP.gif Figure 23. Comparator Application Schematic

9.2.1 Design Requirements

For this design example, use the parameters listed in Table 2 as the input parameters.

Table 2. Design Parameters

PARAMETER VALUE
Reference initial accuracy 0.4%
Supply voltage 48 V
Cathode current (IK) 50 µA
Output voltage level 2.5 V to 36 V
Load capacitance 1 nF
Feedback resistor values and accuracy (R1 and R2) 10 kΩ

9.2.2 Detailed Design Procedure

When using TL1431 as a shunt regulator, determine the following:

  • Input voltage range
  • Temperature range
  • Total accuracy
  • Cathode current
  • Reference initial accuracy
  • Output capacitance

9.2.2.1 Programming Output/Cathode Voltage

To program the cathode voltage to a regulated voltage a resistive bridge must be shunted between the cathode and anode pins with the mid point tied to the reference pin. This can be seen in Figure 23, with R1 and R2 being the resistive bridge. The cathode/output voltage in the shunt regulator configuration can be approximated by the equation shown in Figure 23. The cathode voltage can be more accurately determined by taking in to account the cathode current with Equation 1.

Equation 1. Vo = (1 + R1 / R2) × VREF – IREF × R1

For this equation to be valid, TL1431 must be fully biased so that it has enough open loop gain to mitigate any gain error. This can be done by meeting the Imin specification denoted in Electrical Characteristics – TL1431M.

9.2.2.2 Total Accuracy

When programming the output above unity gain (VKA=VREF), TL1431 is susceptible to other errors that may effect the overall accuracy beyond VREF. These errors include:

  • R1 and R2 accuracies
  • VI(dev) – Change in reference voltage over temperature
  • ΔVREF / ΔVKA – Change in reference voltage to the change in cathode voltage
  • |zKA| – Dynamic impedance, causing a change in cathode voltage with cathode current

Worst case cathode voltage can be determined taking all of the variables in to account.

9.2.2.3 Stability

Though TL1431 is stable with no capacitive load, the device that receives the shunt regulator's output voltage could present a capacitive load that is within the TL1431 region of stability, shown in Figure 12. Also, designers may use capacitive loads to improve the transient response or for power supply decoupling. When using additional capacitance between Cathode and Anode, refer to Figure 12.

9.2.2.4 Start-up Time

As shown in Figure 24, TL1431 has a fast response up to approximately 2 V and then slowly charges to its programmed value. This is due to the compensation capacitance the TL1431 has to meet its stability criteria. Despite the secondary delay, TL1431 still has a fast response suitable for many clamp applications.

9.2.3 Application Curve

TL1431 TL1431M g_pulse_resp.gif Figure 24. TL1431 Start-up Response

9.3 System Examples

Table 3 lists example circuits of the TL1431.

Table 3. Table Of Example Circuits

APPLICATION FIGURE
Shunt regulator Figure 25
Single-supply comparator with temperature-compensated threshold Figure 26
Precision high-current series regulator Figure 27
Output control of a three-terminal fixed regulator Figure 28
Higher-current shunt regulator Figure 29
Crowbar Figure 30
Precision 5-V, 1.5-A, 0.5% regulator Figure 31
5-V precision regulator Figure 32
PWM converter with 0.5% reference Figure 33
Voltage monitor Figure 34
Delay timer Figure 35
Precision current limiter Figure 36
Precision constant-current sink Figure 37
TL1431 TL1431M ai_shunt_reg.gif
R must provide cathode current ≥1 mA to the TL1431 at minimum V(BATT).
Figure 25. Shunt Regulator
TL1431 TL1431M ai_prec_high_curr.gif
R must provide cathode current ≥1 mA to the TL1431 at minimum V(BATT).
Figure 27. Precision High-Current Series Regulator
TL1431 TL1431M ai_higher_cur_shunt.gif Figure 29. Higher-Current Shunt Regulator
TL1431 TL1431M ai_prec_5v_15a.gif Figure 31. Precision 5-V, 1.5-A, 0.5% Regulator
TL1431 TL1431M ai_pwn_conv_05ref.gif Figure 33. PWM Converter With 0.5% Reference
TL1431 TL1431M ai_delay_timer.gif Figure 35. Delay Timer
TL1431 TL1431M ai_prec_const_sink.gif Figure 37. Precision Constant-Current Sink
TL1431 TL1431M ai_sngl_supp_comp.gif Figure 26. Single-Supply Comparator
With Temperature-Compensated Threshold
TL1431 TL1431M ai_out_cntrl_3term.gif Figure 28. Output Control Of A
Three-Terminal Fixed Regulator
TL1431 TL1431M ai_crowbar.gif
See the stability boundary conditions in Figure 12 to determine allowable values for C.
Figure 30. Crowbar
TL1431 TL1431M ai_prec_reg_5v.gif
Rb must provide cathode current ≥1 mA to the TL1431.
Figure 32. 5-V Precision Regulator
TL1431 TL1431M ai_volt_monitor.gif
Select R3 and R4 to provide the desired LED intensity and cathode current ≥1 mA to the TL1431.
Figure 34. Voltage Monitor
TL1431 TL1431M ai_prec_curr_limit.gif Figure 36. Precision Current Limiter