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BQ25883: unknown type usb adapter, how to maximize the charging current.

Part Number: BQ25883

Hi experts,

                 My customer IS using bq25883, but charging current can't meet their target,    they used an usb adapter[ 5v 2A] from their end-customer and the battery is 2s Li-Battery ,8V.   BQ25883 can only identify this adapter as unknown device,  so the adapter actually output 500mA current.  to improve this, my customer  try to enable the ICO function and set the REG_0A register to 1000mA, by using multi meter to measure the charging  current, they can see the improvement , the charging current increased from 280mA to 420mA, but still far behind their expectation.  based on this use case, would you please suggest how to maximize the adapter's capability and increase the charging speed. thanks. 

  • Dear Yue,

    The datasheet details the setting of the current limit in Section 8.3.3.2. If the charger detects an unknown 5V adapter, which I think is your case, the input current is set to 500 mA. After the detection, the host can overwrite the IINDPM and VINDPM registers to change the input current limit or the input voltage limit. Please note, however, that the input current limit is the lower of the IINDPM register, the current setting based upon the ILIM pin, or the ICO setting (if enabled).

    In your case, you may have written the IINDPM setting where you want it, but either the ICO or the ILIM pin could be limiting the current still.

    Can you provide me your I2C register status when the charging current is 420 mA? This will help me better diagnose the problem. Also, what is your input current when charging at 420 mA?

    Thanks,

    Please click "This resolved my issue" button if this post answers your question.

  • Dear Michael,

    I'm his customer,and I asked the question.The I2C resister is shown in the figure below.


    Maybe I have written the IINDPM setting 500mA,  either the ICO or the ILIM pin could be limiting the current still.So the charging current is 420mA is Relatively reasonable value.

    Thanks.

  • Can you provide all the registers, including the flags? I need to see if the ICO is even triggered. I think that you may be limited by your ILIM pin right now. How is the ILIM pin connected on your schematic?

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • Dear Michael,

    All the registersand my schematic are shown as the figure below,

    Thanks.

  • I think the problem here is that the fast charge current is set at 400 mA. What happens if you increase the fast charge current register?

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • I have increased the fast charge current register.It seems to work. bq25883 connects to MCU.But unpluging the adapter and pluging it in again to charge the device, the charging current is pulled down to a fixed value. For example, when I set 500mA(or a higher value), the actual current is only about 300mA.Will bq25883 change charging current after power on reset?

    Thanks.

  • And  reset the ICO_STAT[1:0] bits to '00' after power on reset.

  • After the input source is qualified, the USB Battery Charging Specification 1.2 (BC1.2) is run. Because you are using a non-standard adapter, your input current limit is probably being set to 500 mA. To me this makes sense from a power perspective. If you are charging at 300 mA with an 8V battery, your battery power is roughly 2.4 W. Assuming a 5 V 500 mA adapter, the most power you could pull is around 2.5 W. With the loss of the converter, the output power of 2.4 W makes sense.

    Can you please read the registers after you re-insert the adapter and verify the Input Current Limit? If it is indeed 500 mA, you will need to update the input current limit to what you know you can handle after the BC1.2 is run.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • OK.My adapter is 5V 2A.It doesn't have D + and D-.

    Due to the lack of connection between D + and D -, the adapter can only be recognized as unknown. In order to improve the charging current, I used FORCE_ICO during power on initialization, but after power on reset, FORCE_ICO did not work. As stated previously,for an unknown adapter ,the most power you could pull is around 2.5 W.In order to increase the charging current for 500mA,What can I do when the adapter is unknown?And thanks for your advice for re-inserting the adapter and verifying the Input Current Limit.I will do it.

    Thanks.

  • You can short the D+/D- pins and this will give an input current limit of 3 A. However, you also need to make sure the ILIM pin is biased such that its current limit is above 3 A. Anytime you would want to lower the input current limit, you would have to write to the part via I2C. That is option 1.

    The second option is to do what you are doing now, but instead write to the part after the BC1.2 is run and update the current limit. This would have to be done every time the adapter is connected.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • Every time the adapter is connected,I update an input current limit of 3 A.It seems ti work.Thank you for your answer.

  • Happy to help!

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