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BQ25616: Charging Configuration and Pre-Charge Current Concerns

Tom Tsao
Expert 1850 points
Part Number: BQ25616

Tool/software:

Hi TI Experts,

We are currently evaluating the BQ25616 for a product with the following requirements and have a few questions:

  1. If D+ and D- lines are connected, how is the charging current (ICHG) determined? Will it rely on the D+/D- charger detection or register configuration?

  2. Can the D+ and D- lines be shared with a USB client interface on an MCU? We require both charging and USB communication functionality on the same connector.

  3. We noticed that the pre-charge current is fixed at 5% of ICHG, and in our case, the battery is 7000mAh, with ICHG = 2A. This results in a pre-charge time of approximately 20 minutes, while competitor solutions offer ~3 minutes.
    Is there any way to increase the pre-charge current with BQ25616, or any recommended workaround to reduce pre-charge time without changing the charger IC?

Thank you for your support!

Best regards,

Tom

  • 0
    TI__Mastermind 40325 points

    Hi Tom,

    1. D+/D- detection determines the input current limit, which can affect the charge current if the input current limit is reached. Assuming the input current limit is not reached, ICHG setting sets the charge current.

    2. There needs to be a multiplexer in between. If USB communication happens during D+/D- detection, the input detection will not work properly. After detection, the MCU can switch to USB communication.

    3. You cannot speed up the precharge anymore.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Expert 1850 points

    Hi Mike,

    Thank you for your reply!

    I have a few more questions I’d like to ask you.

    1.

    Should it be that when the input current exceeds this limit, the charging current is then determined by the ICHG setting?

    3.

    Do you have any recommendations for external circuits to increase the pre-charge current?
    Currently, we have tried connecting the following circuit in parallel to the BAT pin of the BQ25616. When the battery voltage is below 3.0V, it provides additional pre-charge current. Testing shows that it works, but we’d appreciate your help in reviewing whether there are any other potential risks to consider.

    Best regards,

    Tom

  • 0 in reply to Tom Tsao
    TI__Mastermind 40325 points

    Hello Tom,

    1. When the input current exceeds the limit, charge current will be reduced to maintain the load.

    2. This method will burn power through the diode. In addition, it bypasses the internal protection in the BQ25616 as the BQ25616 will only regulate the precharge current coming out of the charger. If in supplement mode, the current will flow through the diode and either to the battery or back through the BATFET depending on the load. This is a potential workaround, however we do not specifically support this application of the IC, please test according to your application. I would make sure this path is disabled during the CV portion of charging, which the diode should facilitate.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Expert 1850 points

    Hi Mike,

    Thank you for your reply!

    Back to the previous question — we have already added a multiplexer to switch the D+/D- lines of the BQ25616. How long does it typically take before we can switch to our system's USB?

    Regards,

    Tom

  • 0 in reply to Tom Tsao
    TI__Mastermind 40325 points

    Hi Tom,

    It depends on the adapter (but usually less than 5s), you should know however because the converter will start switching.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Expert 1850 points

    Hi Mike,

    Do you mean that once the adapter is plugged in, and the converter starts switching and supplying power to the battery, we can then switch the D+/D- lines over to USB communication?

    Regards,

    Tom

  • +1 in reply to Tom Tsao
    TI__Mastermind 40325 points

    Hi Tom,

    Correct.

    Regards,

    Mike Emanuel