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TPS3702: Worst case of threshold voltage

Ryuuichi machida
Guru 11515 points
Part Number: TPS3702

Hello,

Let me confirm about below.

* According to datasheet DC spec, when user will use TPS3702C with ""SET" pin = High".threshold is set to "+/-4%".

In addition, accuracy of threshold is +/-0.9% at over temperature condition. So, worst case will be "+/-4.9%" in this case.

However, according to "Table 2 Design parameters" in datasheet, this shows "+4.94%/-4.86%" as worst case.

The question is

--

* I understood that condition of "Design result" of "Table 2 Design parameters" is measurement value.

In this case, VSENSE measure "3.30132 V", so worst case become "3.30132 * 1.049 = 3.4630(4.94% of "3.3V")" and "3.30132 * 0.951 = 3.1395(4.86% of "3.3V")".

Is my understanding correct ?

--

Best Regards,

  • 0
    TI__Genius 9375 points

    Machida-san,

    If I understand correctly, I think you're asking that if the value measured for Vsense is offset by 0.00132 V in this case, does the worst case also shift in both directions? If that understanding is correct, then I would advise you take 4.94% of 3.30132 V instead and multiple it (similarly also with the UV case and 4.86%).

    This would bring the supposed worst case values to 3.4644 and 3.1409 for OV and UV respectively.

    Thanks,

    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Guru 11515 points

    Hello

    What I would like you to confirm is when "Vsense" voltage exactly match user expected voltage (Ex, Vsense = 3.30000V), worst case of threshold is +/-4.9% or not.

    According to datasheet, it seems +/-4.9% is worst case. However only Table 2 shows "+4.94%, -4.86%".

    I wonder where these values come from.

    My guess is that "Vsense" voltage have offset "0.00132V" in this case(Table 2 condition), so worst case is shift 0.04%.

    BR,

      

  • 0 in reply to Ryuuichi machida
    TI__Genius 9375 points

    Machida-san,

    I understand what you are saying now. I believe that this worst case is due to an offset, as you mentioned, because even the worst case is shifted upwards from what it should be. I'm not sure of the actual baseline, but I believe that 4.94% occurs because of this.

    Thanks,

    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Guru 11515 points

    Hello,

    Thank you for your reply.

    I believe that this worst case is due to an offset, as you mentioned, because even the worst case is shifted upwards from what it should be. I'm not sure of the actual baseline, but I believe that 4.94% occurs because of this.

    How do you consider which portion this "offset" come from ?

    In my case, user will use TPS3702CX50 with "SET pin = HIGH". I understand this means that internal reference is "5.0V".

    If "offset" means offset of internal reference, I believe that this error should be included in +/-4.9% because there is no spec about internal reference.

    My concern is threhold level exceed "+/-5%" due to "offset".

    Could you please tell us what kind "offset" is included in Table 2 of datasheet ?

    Best Regards,

  • 0 in reply to Ryuuichi machida
    TI__Genius 9375 points

    Machida-san,

    The device shouldn't exceed +/- 5% due to any offset. I would focus on the actual electrical characteristics tables rather than the applications found in Table 2. I believe the device should not exceed 4.9% unless there is tolerance issues due to other parts of the application circuit. I will look more into the 4.94% and 4.86% and get back to you on the specifics, but for now I'd stick with the 4.9%.

    Thanks,

    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Guru 11515 points

    Hello Abhinav-san,

     >I would focus on the actual electrical characteristics tables rather than the applications found in Table 2.

    In fact, as you said, we will focus actual electrical charateristics.

    However, Table 2 shows actual usecase based on actual electrical characteristics. So, I'm concerned about this difference.

    Please keep to confirm about which one cause this difference.

    Best Regards,

  • 0 in reply to Ryuuichi machida
    TI__Genius 9375 points

    Machida-san,

    The device should be within the electrical characteristics in the table. Are you concerned about the device exceeding 4.9% or exceeding 4.94%? Since the tolerances are 4.86% and 4.94%, this is still a total of 9.8%, just shifted by 0.04%. 

    Thanks,

    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Guru 11515 points

    Abhinav-san,

    I guess that this difference is caused by following reason.

    * According to datasheet, "threshold accuracy" is defined "-0.9%"(min) and "+0.9%"(max).

    However, correct "threshold accuracy" is "-0.86%"(min) and "0.94%"(max) in fact. Then, TI round up second decimal palce for min and round down decimal palce for max.

    Could you please confirm whether my guess is correct or not ?

    BR,

  • 0 in reply to Ryuuichi machida
    TI__Genius 9375 points

    Machida-san,

    I think I've gotten to the bottom of this. The calculations in Table 2 are a result of calculating 4% of the voltage rail (3.3 V) followed by then calculating 0.9% after that. This results in a shift from what you would expect at 4.9%. Thus if you take \

    UV:

    3.3 V - 4% = 3.168 V

    3.168 V - 0.9% = 3.139 V


    OV:

    3.3 V + 4% = 3.432 V

    3.432 V - 0.9% = 3.463 V

    Hope this resolves the issue.

    Thanks,

    Abhinav.

  • 0 in reply to Abhinav.Sharma
    Guru 11515 points

    Hello Abhinav-san,

    Thank you for your reply.

    Understood.

    BR,