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TPS25221: About Current-limit tolerance

user5054474
Intellectual 320 points
Part Number: TPS25221

I have two questions.

①Does following formula include temperature characteristic?

②Calculation results which used above formula do not match the values of the electrical characteristics as below table.

Especially the smaller value of the IOS has big difference from calculation result.

In the case of RLIM=210kΩ, the calculation results (227mA(min)/261mA(nom)/294mA(max)) which calculated from above formula have big difference from the values of the below table.

Which one is correct?

  • 0
    TI__Mastermind 18031 points

    Hi,

    The table you post is the real test parameters.

    The formula above is the design formula includes the tolerance caused by temperature and process but not include the resistor tolerance.


    You are sure can refer to the fomula above to choose the current limit value.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click'Issue is solved button'.

    Thanks.

  • 0 in reply to Ziv Zhang
    Intellectual 320 points

    Thank you for your answering my question.

    I understood that the formula includes the tolerance caused by temperature and process.

    Assuming that the value of the table is the real test parameters, are there cases in which the current-limit-function works outside the range of caluculated value using the formula?

    227mA(min) / 261mA(nom) / 294mA(max)   max-min=67mA : calculated value, R=210kΩ±0%, includes the tolerance caused by temperature and process

    225mA(min) / 261mA(nom) / 297mA(max)   max-min=72mA : calculated value, R=210kΩ±1%, includes the tolerance caused by temperature and process

    216mA(min) / 261mA(nom) / 309mA(max)   max-min=93mA : calculated value, R=210kΩ±5%, includes the tolerance caused by temperature and process

    210mA(min) /                       / 370mA(max)   max-min=160mA : the real test parameters shown in the table, RILIM=210kΩ, -40℃≦Tj≦125℃

  • 0 in reply to user5054474
    TI__Mastermind 18031 points

    Hi,

    I know your concern.

    I think the datasheet 'variations caused by temperature and process' means little variation of temperature which influence the internal circuit precision.

    The [-40, 125] is the high-low temperaure test which is in more strictly condition.

    The table parameters are got by thousands of IC test and  are guarantteed by TI. You can also refer to the formula and also refer to table3 in Page17.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click'Issue is solved button'.

    Thanks.

  • 0 in reply to Ziv Zhang
    Intellectual 320 points

    Sorry for the late reply.
    After all, what's the reason for the big difference between the guaranteed table parameters values and the values calculated from the formulas?
    Is the guaranteed table parameter values the actual values measured by thousands of IC test plus a margin?
    If so, I guess that the added margin is the reason why the values are different.

  • 0 in reply to user5054474
    TI__Mastermind 18031 points

    Hi,

    Yes, it's considering the real value, the margin and also the CPK value.

    Normally, we can withstand several milliampere trade-off.

    For TI's policy, I will first click resolved button.

    If you have any other concern, contact me any time.

    If you think resolved, please help click'Issue is solved button'.

    Thanks

  • 0 in reply to Ziv Zhang
    Intellectual 320 points

    Hi

    I approve. Thanks a lot!