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

3.2 IKA (Cathode Current)

IKA remains close to 0 as long as VIN stays below the threshold voltage and the cathode voltage is equal to the supply voltage. The supply voltage must be less than the maximum recommended VKA of the shunt regulator. Once VIN crosses the threshold voltage, the cathode terminal starts conducting and cathode voltage remains close to VOL level.

Equation 3. IKA   =(Vsupply-VOL)Rsup

IKA must be in the limits of the maximum recommended operating condition of the device. Please refer to app note slva987 for the impact of IREF and IKA on VOL of the device.

Rsup must be chosen such that IKA in the ON condition is much higher compared to IKA in the OFF condition to make sure that VOH does not degrade.

Equation 4. R s u p ( M a x ) = V O H ( M i n ) I K A   @ ( V I N < V I T )