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BQ25713: Calculate worst case of IDPM on ILIM_HIZ pin

S.Satoshi
Guru 21685 points
Part Number: BQ25713

Hi,

Please let me ask about how to calculate the worst case of IDPM on ILIM_HIZ pin. In this case, I'm considering only the variation of bq25713 and so the resistor value has no variation. Attached calculation includes both REGN variation and input current regulation accuracy, and the result of min/max looks too large. Is this calculation correct? Should I remove input current regulation accuracy that is listed in the lowest?

Best Regards,

Satoshi

  • 0
    TI__Expert 3320 points

    Hi Satoshi,

        Right, when we define this ILIM pin EC table we assume exact 1.2V  present on the ILIM pin. Resistor variation and REGN variation could make it worse, but it should be a very small possibility event.

        By the waay if you don't need to set this IDPM at startup phase, I would suggest you use our REG 3F during steady state for precisely control IDPM. 

    Regards

    Shishuo

  • 0 in reply to Shishuo Zhao
    Guru 21685 points

    Hi Shishuo,

    Thank you for your response. Let me explain the back ground of this question and continue to discuss.

    Now they are considering the startup without no battery, so they'd like to set initial IDPM by ILIM pin. And they need to set the maximum IDPM less than 500mA to meet USB standard.

    And now I'd like to continue to discuss at the case of use exact external voltage present on the ILIM pin. Do you think 300mA setting is reasonable for 500mA max? I think so because the max value is +200mA from typ value in EC table.

    Please note that I do NOT need guaranteed value now. 

    Best Regards,

    Satoshi

  • 0 in reply to S.Satoshi
    TI__Expert 3320 points

    Hi Satoshi,

    Thanks for explanation. I understand your situation here.

    From our experience, ILIM_HIZ pin pull up voltage lower than 1.10V holds potential risk for not successful startup. VSYS will stuck at between 2.8V~3.2V. Shown below there is a startup inrush current, it triggers INDPM if ILIM_HIZ is lower than 1.10V. 

    With this in mind I think it is better to keep  ILIM_HIZ pin setting higher than 1.15V (375mA) giving us some margin.

    Regards

    Shishuo