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BQ24616 Precharge/Fast charge/Termination current regulation accuracy

Rajesh Kaliyaperumal
Intellectual 930 points
Other Parts Discussed in Thread: BQ24616

Hi everyone,

We are using BQ24616 IC for our battery charging function.I would like to clarify a doubt regarding Precharge/Fast charge/Termination current regulation accuracy.In the datasheet  Accuracy of the Precharge/Fast charge/Termination current regulation is shown as in below fig and it varies depends upon the voltage across the sense resistor in mV.

The accuracy should have been as i highlighted above since our sense resistor voltage is similar to the highlighted.But we have not seen that much bigger variation in internal testing activity.Hence I would like anyone to clarify why we are not seeing a variation in accuracy as per the datasheet spec .Will it cause any inaccuracy in future ???

Regards 

Rajesh K

  • 0
    TI__Expert 8690 points

    Hi Rajesh,

    The information on the electrical characteristics is based on statistical data from our samples through testing. We guarantee the min/max range, but the actual accuracy error for any single unit taken from the population can be less than what the datasheet says.

    Regards,
    Steven

  • 0 in reply to Steven Bangdiwala
    Intellectual 930 points

    Hi Steven,

    Thank you for the confirmation.I want to know how do I calculate the Accuracy if my applied voltage across the sense resistor is in between the given  values in the datasheet.

    For example if we take a example of fast charge , My applied voltage across the sense resistor is 7.5mV .It is in between the 5 mV and 20 mV 's accuracy in the datasheet.How do i calculate the Accuracy for my applied voltage of 7.5mV in fast charge ???

    Regards,

    Rajesh K

  • 0 in reply to Rajesh Kaliyaperumal
    TI__Expert 8690 points

    Rajesh,

    For your case, assuming you have sense resistor of 0.01 ohm:
    1. Force VISET to 0.15V (750mA charge current)
    2. Measure SRP-SRN differential voltage
    3. Calculate error between the two: ((SRP-SRN - 7.5mV) / 7.5mV) * 100

    If what you meant is an accuracy min/max spec of 7.5mV, we do not have that data, though the accuracy should be better than 5mV data.

    You could improve your accuracy by increasing your sense resistor to, for example, 0.02 ohms, and have VISET to 0.3V. It will however increase your conduction loss.

    Regards,
    Steven

  • 0 in reply to Steven Bangdiwala
    Intellectual 930 points

    Hi steven,

    But if we use this formula we will be calculating the error in applied voltage only right ? 

    Regards,

    Rajesh K

  • 0 in reply to Rajesh Kaliyaperumal
    TI__Expert 8690 points

    Rajesh,

    The error is due to the internal regulation loop using the VISET1 as the reference point. You want to set your current setting through the ISET1 pin and then see if your regulated output is the expected output that you want (which in this case is 7.5mV for 0.01 ohm at SRP-SRN). You want VISET1 to be as close as possible to 0.15V to remove the error contributed by the voltage reference of VISET1.

    Regards,
    Steven