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BQ25611D: Output power and power source select

Ryan Wang
Prodigy 10 points
Part Number: BQ25611D

Hello there, I have some questions regarding this part and please see below:

1. Suppose this IC has connected to usb c as main input via Vbus and a charged backup battery connected via BAT. USB C will have the priority of supporting power to the system, however, if the system needs to pull the power over what the USB C input can provide, will the power path from backup battery be turned on to support the power? If so, what is the condition and how fast is the switching? 

2. If D+ and D- are left floating, what is the input current limit set to? Is this figure the same as of charging and supporting power?

3. The maximum current output of this IC is Isw which is 3.2A, meaning if using USB C as input the maximum current will be capped at 3.2A . Is this statement correct? 

4. If Vbus does not have USB C present and we only have backup battery connected at Vbat to provide power to the system, is this IC working at boost mode under this condition? Is the maximum current allowed from this battery 10A (ISYS_OCP_Q4) or 1.2A (IBST_ACC)?

  • 0
    TI__Mastermind 40845 points

    Hello,

    1. Please read Section 9.3.5.2 "Dynamic Power Management" and Section 9.3.5.3 "Supplement Mode." The battery charging current will decrease, and go below zero to supplement if needed.

    2. The BQ25611D will detect that as an unknown adapter and change the input current limit to 500 mA. However, the host can reprogram IINDPM register bits after input source detection is complete.

    3. The maximum current that can come out of the SW node is 3.2 A. The maximum input current is also 3.2 A. The maximum charging current is 3 A.

    4. It is only in OTG mode if it is enabled. ISYS_OCP_Q4 is more of a threshold detection, while the max RMS discharge current is 6 A. These apply to discharging the battery through the system. However, the maximum boost output current limit is indeed IBST_ACC.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 10 points

    Hey Mike:

    Thank you for your quick response and it helps! I have the following question though:

    1. For point 4 in the previous message, if OTG mode is NOT enabled and only the battery is used for powering on the system, what is the maximum discharge current allowed on the battery? Would it still be 6A? 

    2. For OTG mode in this post I figured the output is at Vbus, so Ibst_acc would be this current in the screenshot shown below? 

    Thank you!

  • +1 in reply to Ryan Wang
    TI__Mastermind 40845 points

    Hi Ryan,

    1. Yes it would be the 6A to the system.

    2. Yes that is correct.

    Regards,

    Mike Emanuel