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BQ24297: Can the device indicate that the sourcing adapter is unable to source desired load?

John Griffith
Mastermind 21346 points
Part Number: BQ24297
Other Parts Discussed in Thread: BQ24295

Hello,

My customer and I were looking at this app note: https://www.ti.com/lit/an/sluaa94/sluaa94.pdf 

The project he is working with wants to use a 5V 3A wall power adapter. The question we are trying to figure out is if the system needs a 5V, 3A adapter and someone tries to use a 5V, 1A adapter for instance, can the part indicate that there is an issue so the system MCU can send a warning?

Looking at the app note mentioned above the BQ24295, and BQ24297 can both handle 3A for specific applications but can the indicate this type of system "fault"? My limited understanding is that when a device is plugged into over USB there is an enumeration that occurs and a power level is negotiated. Can all of our USB charger devices relay the negotiated charge current to the system MCU? And then if the negotiated charge current it is lower than the desired 3A the micro can send a warning? Please correct me if my basic understanding above is incorrect. 

We are open to other devices, mainly just trying to figure out if this is something all devices can handle, if only some can do this, or if we need to find another way to solve this system level possible issue. 

Thanks in advance! 

John

  • 0
    TI__Mastermind 30075 points

    Hi John,

    Both of these parts have D+/D- detection for BC1.2. When plugged in with proper D+/D- connection, the part will automatically set the current limit according to the specified adapters. Keep in mind the input current limit is the lower of I2C register and ILIM.

    If the battery charger tries to pull more than the BC1.2 or ILIM input current limit, the charger will begin to limit the charge current to supply the system load. As far as an indicator, REG08[3] will go high to indicated IINPDM or VINDPM. This indicates the input adapter is being overdrawn and is using Dynamic Power Management to prioritize system current.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    TI__Mastermind 21346 points

    Hi Mike,

    Thanks for the quick response. Can the MCU on the device that is being plugged in that has the USB charger be able to read what the current limit is set to? And then if it is lower than the desired 3A, it can decide to throw a warning to the user that the USB power adapter is not high enough power for the system?

    John

  • 0 in reply to John Griffith
    TI__Mastermind 30075 points

    Hi John,

    1. The IINLIM register will tell you the recognized input current limit. Please note the ILIM pin connection can lower this.

    2. The one way to know if you are in IINDPM or VINDPM (which means the input power is not sufficient for your charge current and system load) is to see REG08[3] go high.

    Regards,

    Mike Emanuel