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BQ25886: Cost Effective USB C Charger

J.Schweiger
Expert 1745 points
Part Number: BQ25886
Other Parts Discussed in Thread: BQ25792, TPS25750,

Hello,

I have an application that has 2x 18650 batteries (7.4V, 2600mAH) and need to charge them from USB adapter.

My client wants to use a USB type-C connector, but we cannot have cost of full USB PD (we considered BQ25792 + TPS25750).  For this reason, I'm now planning to use the BQ25886 which will be limited to 15W (5V, 3A), but is much lower cost.  Any thoughts on this approach would be appreciated, but isn't the main question I have.

The question I have is how to connect the D+/D- pins of the BQ25886 with USB C.  My understanding is that with USB C current limits are set via CC1/CC2 pins, while older USB current limits are set via D+/D-.  I also realize that USB C has two pairs of D+/D-, and many USB C connectors are designed for power-only (no data), with just GND, Vbus, and CC1/CC2.

How do you suggest connecting the BQ25866 to a USB C connector for best compatibility?  Should I connect the D+/D- pins of the IC to both pairs of D+/D- on USB-C (e.g. is it possible to have legacy adapter requiring the D+/D- negotiation with USB C cable)?  Should I also add in the pulldowns on CC1/CC2 in case a USB-C style of adapter is used?

Note that in my design we do not have an MCU and no need for data over USB.

I look forward to any insights you can provide.
Kind Regards,
-Jon

  • +1
    TI__Genius 11850 points

    Hi Jon,

     

    We currently do not have a charger IC in our portfolio with integrated USB Type-C communication. You may need a dedicated USB controller for USB Type-C communication.

     

    If you are only using the BQ25886 without a host MCU or USB Type-C controller, then you will have to use the BQ25886's integrated BC1.2 detection using D+/D-. One option is to short the D+/D- pins together and rely on the ICO algorithm to set the appropriate input current limit. When the D+/D- pins are shorted together, the BQ25886 detects a DCP and sets the input current limit to 3A. The ICO algorithm then identifies the maximum input current limit without overloading the input source. Section 8.3.4 in the datasheet provides more details about this.

     

    Here are some related E2E threads for your reference, as well as an app note discussing ICO:

    https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/954086/bq25886-type-c

    https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/975204/bq24250-bq24250-to-usb-c-connection

    https://www.ti.com/lit/an/slva812c/slva812c.pdf 

     

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Expert 1745 points

    Thank you Angelo.  I apologize for the delay in getting back. 

    As I'm only looking for a 5V output, my understanding is I don't need the full PD controller (as noted in the first thread you linked).  I do want to be able to pull 3A, but my understanding is USB C type chargers would use a simple 5.1k pulldown resistor on CC1/CC2 line to be recognized as an UFP and allow full 5V/3A.  If a legacy USB charger (e.g. BC1.2) is connected, I would like it to work which is why I asked about connecting to the two D+/D- connections from USB C connector. 

    I'm leaning towards having the full USB C connector, connecting the 5.1k pulldowns in case a USB C charger is connected and connecting both D+/D- connections into the BQ25866. 

    From your response, I'm now concerned if the BQ25866 needs to see something on D+/D- pins in order to accept the charge.  When you said to short D+/D-, were you talking about the pins from the USB C connector or are you talking about the pins on the BQ25866? 

    I'd appreciate your suggestion on how to optimize the compatibility with chargers as I'm sure that consumers will try to connect whatever adapter they have.

    Thank you,
    -Jon

  • 0 in reply to J.Schweiger
    TI__Genius 11850 points

    Hi Jon,

     

    In order to allow up to 3A of input current from the adapter, you can short the BQ25886's D+ and D- pins together so that the BQ25886 detects a DCP and sets the input current limit to 3A. You don't need to connect the BQ25886's D+ and D- pins to anything else. In this case, the actual input current limit used by the BQ25886 is the lower value between the ILIM pin setting and ICO. If possible, I recommend ordering a BQ25886 EVM so you can evaluate these functions and determine whether they meet your application requirements.

     

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Expert 1745 points

    Thank you.  So it sounds like there is no perfect solution.

    Option 1: Short D+/D- pins of BQ25886 to accept full 5V/3A from USB C Charger.  Downside is if BC1.2 charger is connected, the charger will not get the required D+/D- communication to provide full power.

    Option 2: Connect D+/D- pins of BQ25866 to D+/D- pins (both groups) on USB C connector. This will provide full 5V/3A from legacy BC1.2 charger, but would fail with USB C Charger because BQ25866 won't accept current without connection on D+/D-.

    Am I correct in my understanding here?  It seems odd to me that we cannot be compatible to both BC1.2 and USB C.

    Best Regards,
    -Jon

  • +1 in reply to J.Schweiger
    TI__Genius 10240 points

    Jon,

    Your understand is correct that there is no perfect solution here.

    Option 1: Configure for 3A input current and the BC1.2 cases would reply on Input Voltage Dynamic Power Management (VINDPM) to get the full power. This might be a good option for both BC1.2 and USB-C, but it is not perfect.  

    Option 2: D+D- connection would work for BC1.2 input source, but does not work for USB-C.