SNVAA58 December   2022 ATL431 , ATL431LI , TL431 , TL431LI

 

  1.    Abstract
  2. 1Trademarks
  3. 2Comparator Mode
    1. 2.1 Input Threshold Voltage (VIT)
    2. 2.2 Output Levels (VOH , VOL)
    3. 2.3 Propagation Delay
  4. 3Design Parameters for Comparator Mode
    1. 3.1 IREF (Reference Current)
    2. 3.2 IKA (Cathode Current)
    3. 3.3 Stability
      1. 3.3.1 Load Capacitor (Cathode to Anode)
      2. 3.3.2 Compensation in Comparator Mode in Feedback of PWM Controller
  5. 4Design Example
    1. 4.1 Input Parameters
    2. 4.2 Specs of Comparator Mode
  6. 5Conclusion
  7. 6Revision History

4.1 Input Parameters

Table 4-1 lists all the input conditions for a design example show in Figure 4-1

Table 4-1 Design Parameters
Parameter Value
VPU 10 V
Vin Threshold = 5, Maximum Vin = 6 V
Device TL431 [VREF = 2.495, IKA maximum = 100 mA , IKA min = 1 mA ]
IKA (as per design budget) 10 mA

Calculations

  • Max Iref Variation = 100 uA

  • R1 can be calculated from equation 3 , R1 = 35 kΩ
Equation 5. R2=R1хVREFVKA-VREF
  • R2 - 35 kΩ
  • RPU can be calculated from equation 3 , RPU = 800 Ω
  • This design does not use any load capacitor. However, the designer can put a load capacitor from cathode to anode as discussed in Section 3.3.