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BQ25303J: How to determine RICHG (at a constant current)

?? ??
Prodigy 10 points
Part Number: BQ25303J

Please tell me how to determine the parameter KICHG for determining the charging current or RICHG for determining the charging current.

I referred to Figures 8-5 and 8-6 on page 12 of the data sheet, but I couldn't figure out how much resistance should be put in to get the expected charging current.

Please show how to calculate KICHG with a formula.

  • 0
    TI__Genius 10240 points

    Hi there,

    Please refer to the Page 23 of the BQ25303J datasheet Section 10.2.1.2.2 Charging Current Setting, The R can be calculated with the RICHG = KICHG / ICHG. The charging current ICHG is known from the design specifications. Figure 8-5 can be used to to find the KICHG for the given ICHG.

    Regards,

    Eric 

  • 0 in reply to ezhao
    Prodigy 10 points

    Thank you for reply.

    I want to set ICHG to 700mA, but I couldn't read the KICHG value at 700mA accurately from Figure 8-5 .

    Therefore, I would like to know if there is a formula to calculate KICHG when you want to make ICHG a certain current.

  • 0 in reply to ?? ??
    TI__Genius 10240 points

    Hi there,

    The K=40250 AOhm should be a close number for ICHG=700mA. As the scale of the vertical axis is very fine. The deviation of +-40Aohm will only generate about +-0.1% error. The resistor's selection is likely to dominate the overall accuracy.  

    Regards,

    Eric 

  • +1 in reply to ezhao
    Prodigy 10 points

    Is it okay to understand as follows?

    Read KICHG with the current values set from Figure 8-5. At this time, the value to be read is an approximate value, but the reading error (about ± 40 Aohm) is 0.1% of the representative value. Therefore, there is no problem because the error due to the selected resistance becomes dominant.

  • 0 in reply to ?? ??
    TI__Genius 10240 points

    Yes, your understanding is correct.

    Regards,

    Eric