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ATL431: IKA value when VKA is not equal to VREF

Hiroshi Sato
Expert 2590 points
Part Number: ATL431
Other Parts Discussed in Thread: TL431,

Hello,

Our customer trying to change from TL431 to ATL431 due to low IKA.

Their usage is VREF voltage differ from VKA, there is no data in such condition in the datasheet.

They know that their condition is not general so the datasheet do not show the data,

however, they want to know them for compare with their measurement results.

Could you give VKA vs IKA data or graph when VKA is not equal to VREF.

I attach the circuit that they are going to build, please check it.

Thanks and best regards,

Hiro

ATL431-TL431.xlsx

  • 0
    TI__Expert 3835 points

    Hi Hiroshi-San,

    The ATL431 is being used in an open-loop (comparator) mode. Based on your circuit attached, the nominal voltage is 12V with a REF voltage of 1.89V. Since this is lower than the 2.5V bandgap reference, the cathode will be high impedance and pull up to VDD. In this case, the Ika is minimal.

    When the REF voltage approaches closer to 2.5V (15.9V threshold voltage), the cathode voltage will pull closer to its reference ~2V. In this case you can calculate the Ika based on Vdd, and cathode resistors R8,R9. 

    Hope this helps,

    Ethan

  • 0 in reply to Ethan T
    Expert 2590 points

    Hello Ethan-san,

    Thank you for your explanation, I told that the customer.

    Excuse me,  they have new questions,

    please check the attached file and give us your advice .

    Thanks and best regards,

    Hiro

    ATL431inquirt20180712.xlsx

  • 0 in reply to Hiroshi Sato
    TI__Expert 3835 points

    HI Hiroshi-San,

    See my feedback below:

    Q1: We do not characterize the device since this device is used out of its normal mode of operation (closed-loop). The behavior is interesting since the delta should not be that high when REF is under 2.5V.

    Q2: I believe the capacitor countermeasure is a good solution and the startup delay is just a trade off. It is possible there is not enough input resistance at the REF current which is make the Vka to shift. I would either add larger resistor dividers (same ratio) or put a series resistor at the REF pin (10K-100K).

    Q3: The Ika curve will be similar to Figure 4 in behavior. 

    Q4: Yes. The cathode voltage will change with temperature deviation and therefore the cathode current.

    Hope this helps,

    Ethan

  • 0 in reply to Ethan T
    Expert 2590 points

    Hello Ethan-san,

    Thank you for your replying.

    I'll explain that and try to make them understand.

    Thanks and best regards,

    Hiro