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TL431 Stability Boundary chart

KIYOSHI NARISAWA1
Expert 1510 points
Other Parts Discussed in Thread: TL431, TL432

Dear TI

There are two figures of the stability bundary condition chart as figure15 and figure16 on TL431 datasheet.

 And aslo there are two figures on application report of "Understanding Satbility Boundary Conditions Charts in TL431,TL432 Datasheet" as figure1 and . 

http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=slva482&fileType=pdf

But Stability chart  are different between figure16 of datasheet and  figure2 of apps note even if there are same devices.

Below figure is on datasheet.

  

and below figure is on applicaton reports.

Coud you show me the reason why these are different?

Thank you and best regards

K.Narisawa

 

 

 

 

  • 0
    TI__Guru*** 140136 points
    Narisawa-san,

    Data sheet chart shows typical 0 degree phase margin lines. Application note shows 30 degree phase margin lines.
    The TL431 is designed to be stable with no capacitor and to have a high bandwidth. Therefore it doesn't work well with most capacitors unless the capacitors have a series resistance to make a zero before unity loop gain.
  • 0 in reply to Ron Michallick
    Expert 1510 points

    Ronald-san,

    Thank you for your explanation.

    BTW,

    is there any stability boundary data for all TL431 and TL431A(except for SOT23-3,SC-70,and Q-Temp devices ) with 30degree as same as application note?

    Thank you and best regards

    K.Narisawa

  • 0 in reply to KIYOSHI NARISAWA1
    TI__Guru*** 140136 points
    Narisawa-san,

    In the data sheet, both stability charts are nearly the same except for "A" line on high end of capacitance.

    I do not have data but it will be similar the app note chart of the left side of chart and "A" line on right side will be pushed out.
    Do you have a specific VKA, IKA, and capacitance that will be used?
  • 0 in reply to Ron Michallick
    Expert 1510 points

    Ronald-san,

    Thank you os much.

    I don't have specification for them.

    Customer had oscillatoin trouble in accoring to select capacitor value in datasheet chart, and then they knew the different chart in apps note.

    So they asked a question for that differenciatoin.

    Thank you and best regards

    K.Narisawa