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BQ25895: Do I need D+/D- detection?

Yaroslav Kukharuk
Prodigy 20 points
Part Number: BQ25895
Other Parts Discussed in Thread: TS3USB221

Tool/software:

Hi

I'm designing my power circuit based on BQ25895, and I'm not sure if I need to use D+/D- pins.

BQ25895 will be used in a portable device, that would use USB-C (5v 3A) for charging and data communication with MCU (firmware updates etc). It would be connected to PC and various charging adapters, so I'm aiming to support 3A input current.
As I understand from the datasheet and various topics on this forum, I can use data lines to detect the source type, thus adapting max current. And to make it work properly, the data lines mux would be required.

Also, there is VINDPM threshold setting algorithm, which kinda does the same/similar thing.

So my question is, can I not use D+/D- for input current detection, and rely on the VINDPM? Is there something important I may lose if I don't use data line detection pins? 

  • 0
    Prodigy 20 points

    I'm mixed up therms. I'm referring to Dynamic Power Management as an alternative to D+/D- based input detection

  • 0
    Prodigy 20 points

    If my assumption about Dynamic Power Management is correct, please review my PCB design, does it make sense to you? Thanks!

     

  • 0 in reply to Yaroslav Kukharuk
    TI__Mastermind 31140 points

    Hi Yaroslav, 

    Thank you for reaching out via E2E. Please see my comments below. 

    Yaroslav Kukharuk said:
    So my question is, can I not use D+/D- for input current detection, and rely on the VINDPM?

    The only feature lost by not using D+/D- pins is the ability to detect different input adapter types and set input current limit (IINDPM) automatically. The input current limit is a hard upper limit on the current the BQ25895 will attempt to draw. Shorting D+/D- pins together will set IINDPM to 1.5A, but this value can be overwritten by I2C control. 

    On the other hand the VINDPM threshold (input voltage limit) acts as a lower limit. If input voltage begins to fall due to adapter being overloaded (example adapter only rated for 1.5A but input current limit set to 3A) device will reduce charge current in effort to not crash input supply. 

    The dynamic power management feature utilizes both input current limit and input voltage limit settings as described in datasheet section 8.2.6.2. 

    Some customers prefer to have an accurate IINDPM setting as opposed to relying on VINDPM because they do not like their input adapters being constantly overloaded. If you are comfortable with this you are free to rely on VINDPM. 

    For schematic and layout review I see no major issues on the BQ25895 portion. The schematic includes all required components and the layout appears to follow our layout guidelines listed in the datasheet on page 55. 

    Best Regards,

    Garrett 

  • 0 in reply to Garrett Kreger
    Prodigy 20 points

    Thanks, Garret, I appreciate your help!

    I have a few clarifying questions:

    1. with default IINDPM (1.5A), and connected USB2.0 adapter, the input current will eventually settle at 0.5A, and the current limit will be maintained for the duration of connection? (meaning BQ25895 won't try to increase the charge current)
    2.  If 1 is correct, what side effects the adapter overload may cause? (My application is a portable device, that will be connected mostly for charging and sometimes for data transfer to PC, wall chargers, powerbanks, etc) 
    3. If I decide to connect data lines to the charger, can I share data lines with my main MCU? Do the same USB HS spec requirements apply to the data lines to the charger?

    Thanks!

  • 0 in reply to Yaroslav Kukharuk
    TI__Mastermind 31140 points

    Hi Yaroslav, 

    For question 1 are you using D+/D- connection or not? For my answer below I am assuming you are shorting pins together to result in 1.5A detection. Please correct me if this assumption is wrong. 

    1)With IINDPM = 1.5A setting the device will initially attempt to draw up to this current assuming charge current and system current draw are high enough. It will eventually settle at 0.5A (assuming adapter is only rated for 0.5A) due to input current optimizer (ICO) feature, which is described in section 8.2.4 of the datasheet. 

    2)Any side effects of overload will be on the adapter side. As this is not a TI made part I cannot on specific concerns. In general repeatedly overloading an adapter could potentially result in damage.

    3)If you share D+/D- pins with the main MCU it is recommended to use a multiplexer such as the TS3USB221 used on the BQ25895EVM board to ensure lines are isolated for input type detection. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 20 points

    Initially, I was planing to short data lines on the charger ic. But since you mentioned possible adapter overload, I am reconsidering this approach. 

    is it correct to assume that requirements for the data lines from multiplexer to the charger IC does not have typical usb data lines requirements?

  • 0 in reply to Yaroslav Kukharuk
    TI__Mastermind 31140 points

    Hi Yaroslav, 

    The charger IC does not have typical USB data line requirements. It will not attempt to use the D+/D- lines for data only for initial BC1.2 detection. 

    Yaroslav Kukharuk said:
    But since you mentioned possible adapter overload, I am reconsidering this approach.

    I should have mentioned in my original reply, but ICO feature will help to limit adapter overload. It will not fully eliminate chance of adapter overload, but will help to lower input current limit from 1.5A when a lower rated input adapter is used. 

    Best Regards,

    Garrett