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.

TIC12400-Q1: Inquire about INx input voltage level

Part Number: TIC12400-Q1
Other Parts Discussed in Thread: TIC12400

Hi team. 

My customer wants to apply the TIC12400-Q1 to a 36V automotive system.

To solve the input voltage range problem, the TIC12400-Q1 power supply will be supplied 12V using dc-dc.

So I want to check if there are any problems below.

1. When inputting with high signal through IN0 ~ IN9, is there any problem in function even if input by voltage distribution as shown below?

2. When 12V is spplied to VS of TIC12400-Q1, if a voltage of more then 12V(less than 35V) is input to INx, does the function of TIC12400-Q1 problem occur?

Thank you

  • Hi Charles,

    I am assuming 35V or 36V only exist because of battery cranking event. Therefore, it is a transient event rather than long-term DC stress on INx pin. In such cranking case, there should not be any issues. Please correct me if this assumption is incorrect.


    As for your 1st question, the schematic looks good to me. It should be able to correctly detect switch state. However, I am curious why Radd is needed. Here is my analysis.

    With Radd
    Switch Close: VINx = 36V * 2K/(2K + 600) -2mA * (600 * 2K )/ (600+2K) = 26.7V
    Switch Open: VINX = 0V

    Without Radd
    Switch Close: VINx = 36V - 2mA * 600Ohms = 34.8V
    Switch Open: VINx = 0V

    In both with and without Radd case, TIC12400-Q1 should be able to detect the switch state.
  • Hi Fan,

    Thank you for your fast replying.

    Up to 52V can be input when conducting transient voltage tests.

    I would like to apply voltage distribution for the above problem.

    Then, If input voltage of INx exceeds threshold voltage after inputting voltage of less than 35V using voltage distribution, input detection will not be a problem?

    Thank you!

  • Hi Charles,

    52V present at the INx pin would be too high even though over voltage protection exsits in TIC12400-Q1 INx pin. A TVS diode should be able to handle over voltage event.

    If you can share with me what type of voltage distribution you applied to your question, I can help with its reliability analysis.

    As for your last question regarding the voltage threshold, I will appreciate if you could draw a schematic and let me know your concern.
  • Hi Fan Wang,

    Thank you for your fast replying.

    46V TVS diode applied to battery power input for loaddump protection.
    The maximum breakdown voltage of the TVS diode is 52V.
    We are currently designing the circuit and are considering resistor distribution to protect the INx pin.
    (Vs input voltage is protected by applying 12V DC-DC.)

    In addition, reverse protection diode is applied to the battery input.
    Will not current flow through Vs when a -36V voltage is input to INx?

    Thank you!
  • Thanks, Charles. Now I understand why you want to add the voltage divider. Your TVS is 46V with 52V breakdown. In other words, without voltage divider, 46V~52V transient voltage will be present at INx pin.

    As you suggested, reverse protection diode on Vs line is a must. 

    As for your -36V input to INx pin while Vs = 12V, the problem is not current back-flow. The problem is INx pin can only tolerate down to -24V on INx pin while Vs = 12V. If you could bring the INx pin voltage higher than -24V, current back-flow should not be an issue. 

  • Thank Fan,

    In my case, I connected Vin(Battery) to GND and INx to +36V.

    And I added reverse protection diode between Vin to Vs in TIC12400.

    In this case, I think that current does not flow due to the reverse current protection diode.

    But, INx was below -24V and exceeded the maximum voltage rating.

    In this situation, Is there any problems in INx?

    Please check as soon as possible.

    Thank you.

  • Hi Charles,

    Yes, there will be an issue in this case. When INx voltage is below -24, current is not biggest concern compared to voltage. This voltage exceeds the max rating. In other words, it's going to permantly damage the internal transistor.