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BQ25798: BQ25798 type C query

Part Number: BQ25798
Other Parts Discussed in Thread: TPS25750, , BQ25792, TUSB422


Dual input of solar energy and type C, type C is preferred, and there will be built-in battery and expanded backup battery.

1, The D+ and D - of BQ25798 support the detection of BC1.2. When using Type C, is it can directly connect DP and DM Pin, or use the CC control logic chip, such as TPS25750?

2, Whether the D+ and D - of Q25798 can also be used as data channels to transmit data while performing USB PD detection?

3, When solar energy and type C dual input are used, back-to-back MOS tubes are used on each channel. Is there current backflow when there is voltage input at the same time, for example, 21.7V of solar energy backflow current into 5V of type C?

4, For the battery part, 2 series of built-in batteries are the default ones of the system, and 2 series of extended batteries are pluggable. Can they be designed with 2S2P? Does plugging and unplugging of extended batteries affect BQ25798?

Waiting for your reply.



  • Hi Star,

    Regarding 1, I recommend using the TPS25750 but it will depend on the TPS25750 firmware.  That's how our reference design appears to do it per the block diagram.

    Regarding 2, no.  During the first 2 seconds after power up at VBUS, the charger needs complete control of the D+/D- lines.

    Regarding 3, no.  Only one input source at a type is allowed by the ACDRVx logic and the back-to-back FETs block back flow.

    Regarding 4, those batteries will try to self balance at plug in.  So the charger may not work as configured for a few seconds until the self balancing completes.  The safety timer and/or charge current may need to increase in order to complete the charge cycle in the desired time.



  • Hi Jeff

    Thanks for your help.

    Regarding question 1, I have the following queries.
    a) Does TPS25750 require separate firmware? I think it does not require firmware development according to the introductions below.
         *Standalone USB Type-C PD Solution
         *No firmware development or external microcontroller required
    b) If the BC 1.2 function of BQ25789 is not recommended for Type C, can Type A use its BC1.2 feature?
    c) If the USB power supply function of BQ25798 is not used, is there a more suitable chip combination of Charger+TPS25750 with MPPT function? It should have low static power consumption.
    d) In the Type C connector, is CC only used for voltage control, and will DP and DM no longer conduct voltage negotiation?
    e) Is there a CC control logic chip, which can be negotiated into a Slink device after being connected to Type C, and the VBUS of Type C is used as one of the dual inputs of BQ25798? The functions of TPS25750 are quite comprehensive, and the ability of its USB Source cannot be put into use when used with BQ25798. Its ability is wasted.

    Regarding question 2: Will the D+ and D- controlled in this 2s affect the MCU? If D+ and D- are occupied during the negotiation process, can it be used normally after the negotiation is completed? Our scenario accepts operations after 2s.

    Waiting for your reply.



  • HI Star,

    Regarding 1a. TPS25750 requires firmware.  The PSIL team has already developed the firmware and it has been loaded to the TPS25750.  If it works for your application, then no changes to the firmware are needed. 

    Regarding 1b, The TPS25750 firmware writes to the charger's input current limit after USB C negotiation.  So, I suppose you could use the D+/D- feature on the charger but the TPS25750 might overwrite the value. Actually, you will need to ask the firmware team if the TPS25750 firmware disables auto D+/D- detection. If so, then you can't use it.

    Regarding 1c, the original firmware was written for BQ25792 which does not have MPPT.  There is no TPS25750 firmware version that has been optimized for use with MPPT and BQ25798. So, if you use that firmware, another host will need to enable MPPT on BQ25798.

    Regarding 1d, CCx lines are used for output current and voltage negotiation.

    Regarding 1e, you will have to ask the USB team.  The only other TI type C non-port controller, communication devices that I know are the TUSB422 and TUS32x. 

    Regarding 2, yes.  The charger's D+/D-, if enabled, goes HiZ after power up negotiation completes.