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.

TPS3701: Using only undervoltage option for a rail different than VDD

Part Number: TPS3701
Other Parts Discussed in Thread: TPS38A-Q1

Hi Team,

I am using TPS3701. 

1. For monitoring only undervoltage (only INA) of a rail which is different from VDD, how to calculate R1 and R2? There is no detail specified in datasheet for this configuration.

2. Any alternate part suggestion which does undervoltage monitoring for both INA and INB?

Thanks,

Vidhya

  • Hi Vidhya,

    Below shows the input threshold voltage that I have circled:

    You can use the 405.5mV as the reference voltage to deassert the output and 400mV to assert the output.

    Regarding to your second question, we do have have several multichannel parts that can meet your dual input undervoltage threshold detection needs.  May I ask what is the application?  Do you need automotive qualified parts?  I am thinking the TPS38A-Q1 as a possible solution to your needs.  Another option is the TPS3704-Q1.

    Please let me know if you have any other questions.  Good luck!

    Ben 

  • Hello Ben,

    For1,  There is no R3 for only UV monitoring? But R1 calculation is based on R3 (OV threshold) as per datasheet.

    How to compute only R1 and R2?Please explain.

    For2, It is for industrial application. Please suggest both channels for undervoltage. Allowing monitoring of 15V and 9V. 

    Thanks,

    Vidhya

  • Hi Vidhya,

    Is your application setup is similar to Figure 24?  See below:

    The output waveform is show below for input B:

    So, for input B, when INB = 400mV, the output will assert low.  The equation will be

    VINB = 400mV * (R4/(R3+R4)) 

    The output waveform is show below for input A:

    So, for input A, when INA = 405.5mV, the output will deassert high.  The equation will be

    VINA = 405.5mV * (R2/(R1+R2)) 

    Please let me know if you have any other questions.

    Ben 

  • Hi Ben,

    yes. I need only undervoltage feature. So R1, R2 has to be calculated with UV threshold.VIT-(INA+) and current through the resistor. The formula that you shared doesn't show the UV threshold. Please clarify.

    Also, suggest a part which supports both channels as UV for industrial application. 15V and 9V are the rails to be monitored.

    Thanks,

    Vidhya

  • Hi Vidhya,

    The UV threshold is what you set by adjusting the resistor values.  For example, if you want to have UV threshold of 2.9V where you are monitoring a 3.3V rail.  Using the equation of 

    VINA = 405.5mV * (R2/(R1+R2)) and assuming R2 is 100Kohms, we can solve for R1.  You know that the threshold voltage is 2.9V so we substitute that value for VINA.

    2.9V = 400mV * (100K/(R1 + 100K))

    R1 = 625Kohms

    This means that for OUTA will go low when VDD is at 2.9V.  When OUTA goes high, VDD = 2.94V.

    For question 2, we do have the TPS38A-Q1 at this time.  Please see the datasheet for more information.  The datasheet for the non-automotive has not been released yet.

    I have a few questions for you:

    1. Is the project at the beginning phase?
    2. What end equipment is the application?
    3. What is estimated volume?

    I hope I have answered your question.

    Ben  

  • Hi Vidhya,

    Are there any new updates?  If not and you are satisfied with the answers that I have provided, please close the thread by clicking on "resolved".  Thanks and good luck to you!

    Ben

  • Hello Ben,

    Thanks for the formula details for only UV monitoring with R1 and R2.

    " This means that for OUTA will go low when VDD is at 2.9V.  When OUTA goes high, VDD = 2.94V."

    what is the behaviour for range of VDD between 2.9V and 2.94V? 

    OUTA goes low?

    Kindly revert. 

    This project is in proto phase for industrial application. 

    Proto quantity is less.

    Thanks,

    Vidhya

  • Hi Vidhya,

    what is the behaviour for range of VDD between 2.9V and 2.94V? 

    The behaviour is shown below in the figure:

    OUTA will fall as the monitored voltage fails below VIT-(INA) and stay low until the monitored voltage is above VIT+(INA).

    Ben

  • Thanks Ben.

    Also the formula has to be 400mV = 2.9V * (100K/(R1 + 100K)) instead of 2.9V = 400mV * (100K/(R1 + 100K))

    Please clarify.

    Regards,

    Vidhya

  • Hi Vidhya,

    Yes, you are correct.  What I should have meant was 2.9V = 400mV*((R1+100K)/100K).

    Ben

  • Hi Vidhya,

    If there are no further questions, please close the thread by clicking on "resolved".  Thanks and good luck to you!

    Ben