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TPS25221: current limit threshold

Kelvin Tee
Genius 10035 points
Part Number: TPS25221

Hi

My customer likes to design TPS25221 and the threshold limit is 1.7A but it was not tabulated in the data sheet. Could you fill in the details below?

Desired nominal current limit       Ideal Resistor     IOS Min                ISO Nom              IOS Max

1700mA                                             ?                            ?                            ?                            ?

Rgds
Kelvin

  • 0
    TI__Expert 8980 points
    Hi, Kelvin,

    Please refer to the formula in datasheet(page 13-page 14).
    www.ti.com/.../tps25221.pdf

    Regards,
    Bob

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    Please verify the answer by clicking the green "RESOLVED MY ISSUE " button in case the reply solved your question.
  • 0 in reply to Bob Ma
    TI__Genius 10035 points

    Hi Bob

    Thanks for highlighting the formula. As i follow Fig 24, it only get the estimation of Rlimit value. I believe table 3 derived from a calculator with decimal point accuracy. Could you help to provide the parameter of 1700mA like those tabulated in table 3? 

    We try to convince customer to move from other device to this. Please help to support. Thanks

    Rgds
    Kelvin

  • 0 in reply to Kelvin Tee
    TI__Expert 8980 points

    Hi, Kelvin,

    Seems you didn't understand our datasheet, there's introduction of calculating the value in table3. You just need to follow below steps and use below formula to calculate all the value. Now, I will use this 1700mA as a example to explain you how to calculate it.


    Step 1: Use second formula and desired IOSnom=1700, we can get ideal RILM resistor = 32.46Kohm. Referring to standard value decade for 1% resistor(can use 0.5% or 0.1% to get better result), we get the closest 1% resistor value is 32.4Kohm.

    Step 2: The 1% low RILIM should be 32.4kohm*0.99, the 1% high RILIM should be 32.4kohm*1.01.

    Step3: Use 1st formula and 1% low resistor to calculate actual IOSmax, use 3rd formula and 1% high RILIM to calculate actual IOSmin. Use 2nd formula and closet 1% RILIM to calculate actual IOSnom. From my calculation, IOSnom=1703mA, IOSmin=1548mA, IOSmax=1821mA.

    If you just want to get a result, below is summary:

    Desired IOSnom=1700mA, ideal resistor=32.46kohm, closest 1% resistor=32.4kohm, 1% low resistor=32.1kohm, 1% high resistor=32.7kohm, actual IOSmin=1548mA, actual IOSnom=1703mA, actual IOSmax=1821mA.

    Regards,
    Bob

    --------------------------------------------------------------------------------------------------------------------------------------

    Please verify the answer by clicking the green  "RESOLVED MY ISSUE " button in case the reply solved your question.

  • 0 in reply to Bob Ma
    TI__Genius 10035 points

    Hi Bob

    My fault didn't read through p15-16 on the example of calculation. This clearly helps to understand the calculation.

    Thanks for the support. 


    Rgds
    Kelvin 

  • 0 in reply to Kelvin Tee
    TI__Expert 8980 points
    No problem!

    Regards,
    Bob