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TL431: Ceramic capacitors

Pjs
Intellectual 880 points
Part Number: TL431

Hi, 

I'm using the TL431 to generate a 19V and a -10V reference rail @ 5mA. 

I have 10uF of capacitance on the output but this is a ceramic capacitance with very low ESR. Looking at SLVA482A - do I also need to add some ESR? If using a ceramic capacitor, would this just be adding a series resistor between the capacitor and the cathode? What value would you recommend?

Am I right in thinking the higher the resistance, the higher the deviation in cathode voltage during transients? 

Many thanks

  • 0
    TI__Mastermind 47685 points

    Hi Philip, 

    Adding an ESR would be in series with the 10uF capacitor to GND.  For stability, as a rule of thumb, I would follow figures 1 and 2 in the app note SLVA482A.  I have copied the figures and pasted them below for your reference:

    Ben

  • 0 in reply to Ben C
    Intellectual 880 points

    Hi Ben, 

    Thanks for the quick reply. Can I confirm: 

    Ben C said:
    Adding an ESR would be in series with the 10uF capacitor to GND

    Here you meant that the ESR resistor would sit between the TL431 anode and the GND connection rather than between the Cathode and the Vout? 

    Are there any ESR graphs for the alternate / newer TL431LI or do the figures in SLVA482A apply to the TL431LI also?

    Many thanks

  • +1 in reply to Pjs
    TI__Mastermind 47685 points

    Hi Philip,

    Since ceramic capacitors have low ESRs, you can add a small amount of resistance in series with the capacitor.  The capacitor is connected from the cathode to the anode of the TL431.  I have included a link for you for your reference:

    https://circuitdigest.com/tutorial/understanding-esr-and-esl-in-capacitors

    I don't believe we have ESR graphs for the TL431LI but I would start the evaluation process with no additional ESR and check for stability.  Here is what I found on the TL431LI for your information:

    Ben

  • 0 in reply to Ben C
    Intellectual 880 points

    Hi Ben, 

    Thanks very much - that's very helpful. 

    Are there any app notes on taking stability measurements on a shunt regulator - can I just provide a disturbance signal at an injection resistor in the feedback network?

    Best regards

  • 0 in reply to Pjs
    TI__Mastermind 47685 points

    Hi Philip,

    Yes, that is one way to evaluate the stability of your circuit.  Another way would be to do a transient load pulse test on the output to which would test stability as well.   

    Ben

  • 0 in reply to Ben C
    TI__Mastermind 47685 points

    Hi Philip,

    If there are no other questions regarding this thread, can you please close the thread by clicking on "resolved"?  Thanks!

    Ben

  • +1 in reply to Ben C
    TI__Mastermind 47685 points

    Hi Philip,

    Just following up with you to see if you have any additional questions for me.  If not, can you close the thread.  Thanks and have a great weekend!

    Ben