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TPS65987DDJ: Question regarding the SLVAE18 method for providing secondary charging power source.

Lauren Mayfield
Expert 7925 points
Part Number: TPS65987DDJ
Other Parts Discussed in Thread: BQ25703A, BQ25895, , TPS65987D, TPS65987, BQ25703

I’ve been reading the SLVAE18 application report for using the TPS65987DDJ as an I2C master to control the BQ25703A and I think the method should work for controlling the BQ25895.

The problem I’m looking for some support with is integrating that solution with a second charging power source. We would like to support the ability to charge and run the product off of POE as well as USB-C. In our case, POE power will only be available when the device is powered on and booted, so the host processor will be available to step in and configure the TPS65987DDJ and BQ25895 as necessary. My thought is to use the method described in SLVAE18 when the product is powered off, then, when the product is powered on the host processor can disable that method and control charging from USB-C and POE directly. The issue with this is making sure that the SLVAE18 method gets re-enabled when the product is shutdown, even if the shutdown is not graceful. One solution would be to reset the TPS65987DDJ and BQ25895 when the product powers off, but that doesn’t seem particularly great.

Is there a better way to do this? Is it possible to have the TPS65987DDJ configure the BQ25895 when POE power is available somehow? If I go down this path, what is the best way to disable the I2C master functions when the product is booted?

Thanks!
Lauren

  • 0
    TI__Mastermind 36756 points

    Hi Lauren,

    You can configure the TPS65987D to only write I2C messages on specific events occurring to the PD controller. For example, you can choose to write when something is either connected or disconnected to the Type-C port. You can also choose to write when the PD controller is booting up by using the Power On Reset event. 

    When the product is booted, you can choose to disable the I2C Master by writing to the Global System Configuration Register on the TPS65987D from your Host controller and disabling the I2C master bit. 

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    TI__Expert 7925 points

    Hi Eric,

     

    Thank you! One follow up question..

     

    The battery chargers (both BQ25703 and BQ25895) require a periodic write to the battery charge current register in order to continue to charge the battery. If the register is not written to for several minutes a watch dog stops the charger. Is there a way to configure the TPS65987 to perform that write periodically?

     

    Thanks,
    Lauren

  • 0 in reply to Lauren Mayfield
    TI__Mastermind 36756 points

    Hi Lauren,

    The TPS65987D in a stand-alone configuration will not be able to periodically write to the battery charger without an event on the Type-C port. However, if there is a host controller within the system, you could use the I2Cw 4CC command to write through the TPS65987D to the battery charger periodically.

    Thank you,
    Eric