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TPS1641: TPS16410 power limit accuracy

Erik Mölstad
Prodigy 10 points
Part Number: TPS1641

Tool/software:

Hi

I am using TPS16410 to help me guarantee that output power is below 15W. (But I want to be close to 15W.)

Vin (and Vout) is 12V

I have Rplim = 100 kOhm   (measured to 100.1 kohm)

And calculate with the below formula that Plim (nominal)= 14.5 W

However, this is not what I measure. Using a DC Electric load and using a current measuring multimeter to confirm current and multiplying with the voltage at the output capacitor of the TPS16410 I consistently get ~15.5W before the eFUSE trigger and block the output, on several units.

Also, I am wondering about the formula above, it does not fully align with the numbers given in the datasheet. Is there a more complicated but correct formula to use? What are the tolerances of this formula?
I would  expect that the +-5% mentioned in the spec are related to the nominal value i.e. 13.69 +-5%, but how should I find the nominal value?

And, are there layout considerations that has to be considered to get accurate power measurements?


Best Regards

  • 0
    TI__Genius 12266 points

    Hello Erik,

    https://dr-download.ti.com/design-tools-simulation/calculation-tool/MD-9RxfrHolEh/1.1.0/TPS1641_Design_Calculator.zip

    You can use the above design calculator for PLIM formula.

    You can expect +-5% to 8% error in PLIM.

    Thanks

    Amrit 

  • 0 in reply to Amrit Jit
    Prodigy 10 points

    First of all, thanks for the calculator, it is very useful and help me double check all my calculations.

    Right now I am measuring, on 3 separate units that the eFUSE output is on at 15.5W with a setting of Rplim=100k ohm (14.37W limit according to the calculator). That is almost exactly +8% of the nominal setting. 

    How does the IC calculate power? it is measuring voltage drop over the internal FET and voltage on the output side of the FET to calculate P? 

    Is the offset such that it is reasonable that all ICs in a batch have the same/similar offset? or would it be expected to be of random distribution? I am asking because I am thinking about if there could be some design or layout related reason for why I see a higher power output than expected.

    Are there any design guidelines regarding how to ensure the device is considered a IEC 62368 PS1 power level?

    I would have expected the IC to stay within +-5% for my usecase (15W load limitation) according to the datasheet. Or is it somewhere specified under what conditions the +-5% is applicable and where +-8% is applicable? 

    //
    TPS16410 TPS16411, TPS16414, and TPS16415
    devices provide ±5% power limiting at 15 W for loads
    and it also provide configurable blanking time for
    transient overload or overcurrent events. TPS16410,
    TPS16411, TPS16414, and TPS16415 can be used
    in low power circuits (LPCs) for 15-W power limiting
    as per IEC60335 and UL60730 standards
     //

  • 0 in reply to Amrit Jit
    Prodigy 10 points

    Basically what I need to know is: @24V what is the highest value for Rplim I can select to be certified as PS1, <15W 

  • 0 in reply to Erik Mölstad
    TI__Genius 12266 points

    Hello Erik,

    Yes, for 15W it's +=5%. Sorry for the previous mistake.

    you select 14W power limit.

    Thanks 

    Amrit