• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 62 subscribers
  • Views 959 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLVH431A stability with capacitive load

Marcel Kaltschmied
Prodigy 50 points
Other Parts Discussed in Thread: TLVH431A, TL431, TLVH431, ATL431

Hi all,

We use the TLVH431A as a voltage reference (cathode and ref pins tied together like on the "Simplified Schematic" on page 1 of datasheet).

My question is, what capacitiy is allowed on the "output pin" for stable operation? In my design I have chosen Ik=250uA and CL=100pF.

In an older datasheet there has been a diagram with stable and unstable regions, depending on the Ik and the load capacity. This diagram has been replaced with Figure 15-17 "phase margin vs capacitive load" in newer datasheets.

I'm not quite shure how to read this diagramm, since in the old datasheet it was Ok to use 10nF with Ik=250uA and now it's not?!

I also saw the Application Report SLVA482A for the TL431. Can this document be used for the TLHV431?

Thank you for your help.

Best regards
Marcel Kaltschmied

  • 0
    TI__Mastermind 24485 points
    Hello Marcel,

    We have replaced the graphs in the TLVH431 datasheet to help make it more clear how much margin there is when designing this device. In the original plots, it was simply a line delineating stable from unstable by looking at 0 degrees phase margin, but this doesn't give enough information to make sure that there is enough margin to cover temperature and process.
    In the old plots, I do not believe that it would have been ok to design with 10nF, because I believe this was in the unstable range. I would not recommend designing with that value because even if it is stable under some circumstances, it likely does not have much margin.

    More than 25 - 30 degrees of phase margin would typically be recommended for this device, so 100pF under the loading conditions that you provided with Vref = Vka should be stable across temperature and process, seeing as this would put you somewhere in the ranger of 35 degrees of phase margin.

    The application report for the TL431 unfortunately does not apply to the TLVH431 as the devices are designed differently and have different stability regions.

    To reduce current consumption further, you may want to also consider looking at the ATL431 device, which has an Ikmin(MAX) value of 35uA. That is if you are willing to use a 2.5V reference vs. the 1.25V reference you are currently using.

    Feel free to let me know if you have additional questions, and I would be happy to help!

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Prodigy 50 points
    Hi Michael,

    Thank you for your detailed answer. That really helped me a lot.

    Best regards
    Marcel