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TPS25751: Charger settings override on USB connect

Sebastien Gravel
Prodigy 40 points
Part Number: TPS25751
Other Parts Discussed in Thread: BQ25756, , BQ28Z620

Tool/software:

Hi,

We are developping a product which uses the TPS25751 USB controller with the BQ25756 battery charger.

The product is capable to be charged from an external source or charge an external device (we call this the power bank mode).

We want to be able to stop this power bank mode by disabling the reverse power path feature in the battery charger.

However, we noticed that, every time a new USB device is connected, the USB controller overrides the battery charger settings, which re-enables the reverse power path and other features such as PFM.

Is there a way to avoid the USB controller to overrides the USB settings at each connection or set different default values in the USB controller to be written in the charger?

Thanks in advance

  • +1
    TI__Mastermind 35736 points

    Hi Sebastien, 

    TPS25751 will automatically enable reverse mode of BQ25756 when the system assumes the Source Power role (providing power to a connected far-end device). You can configure TPS25751 to advertise its source PDO to with maximum current capability of 0A in its Transmit Source Capabilities register (0x32) which TPS25751 will then use to configure BQ25756 reverse current to 0A. After modifying the Transmit Source Capabilities register, the MCU will then need to send 4CC command "SSrC" to instruct TPS25751 to send its new source capabilities to the connected port partner. 

    Let us know if you have any further questions or concerns! 

    Thanks and Regards,

    Raymond Lin

  • 0 in reply to Raymond Lin
    Prodigy 40 points

    Thank you for your input.

    In the same kind of problem, is there a way to change the default value of other settings like EN_PFM or EN_TERM in the TPS25751 binary image?

    We have an issue where, if the BMS disconnects the battery, connecting an external USB source periodically cuts power after the charger.

    We think this occurs because the charge termination keeps stopping the charger since no current is flowing to the battery.

    Since this power rail is also powering our MCU, we cannot clear the EN_TERM using the MCU.

    In other term, we would need the TPS25751+BQ25756 to autonomously configure themselves to disable charge termination and always output power when a USB source is connected.

    Is this possible? I have looked at the USBCPD Application Customization Tool and could not find an option to remove charge termination.

    Regards,

    Sebastien

  • 0 in reply to Sebastien Gravel
    TI__Mastermind 35736 points

    Hi Sebastien, 

    TPS25751 integrated I2C control for BQ25756 is not configurable via GUI or binary image. You could configure BQ25756 termination current (ITERM) to be lower value through the GUI questionnaire and see if that improves the behavior. I'll loop in the BQ team for further support on the charge termination query. 

    Thanks and Regards,

    Raymond Lin

  • 0 in reply to Raymond Lin
    TI__Mastermind 32456 points

    Hello Sebastien,

    Thanks for working on this. I'm the applications engineer for the BQ25756.

    Is it possible for the MCU to write EN_TERM=0 before the BMS disconnects the battery?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 40 points

    Hi,

    In normal operation we can do it. However, we are having issues with the BMS (BQ28Z620) were it sometimes opens the FETs for unknown reason and stays that way until the battery is removed and re-installed.

    When that happens, we would like to be able to connect a USB source and have the output of the charger powering the entire system to be able to power the MCU and maybe reset the BMS registers to close the FETs again.

    Since the system consumes less than the minimum 250mA termination current, it looks like the charger immediatly stops powering the system and retry again a few seconds later. At least, this is my hypothesis. I might be wrong about the reason why the charger only briefly gives pulses of power. The pulses are not long enough for the MCU to be reprogrammed so it is difficult to recover the board.

    Do you have any suggestion on any ways to have the charger holding its output voltage by default, even if the current consumption is below 250mA?

    Thanks,

    Sebastien

  • 0 in reply to Sebastien Gravel
    TI__Mastermind 32456 points

    Hello Sebastien,

    Got it, so the BQ25756 is powering up from a cold start here right?

    The charger is probably charging up the output capacitors, reaching the termination current, and stopping switching. The power on the capacitors then drops to the recharge threshold and the charging starts switching again.

    Can you increase the capacitance by the input of the MCU to make sure the MCU gets enough power?

    Also, what's the charge voltage set to on the BQ25756?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 40 points

    Hi Ethan,

    Yes, it is powering up from cold start.

    By increasing the capacitance to make the MCU gets enough power, you mean enough power to clear the EN_TERM before the power goes out?

    The charge voltage is 8.3V for the charger.

    Regards,

    Sébastien

  • 0 in reply to Sebastien Gravel
    TI__Mastermind 32456 points

    Hi Sebastien,

    Thanks for the clarification.

    Sebastien Gravel said:
    By increasing the capacitance to make the MCU gets enough power, you mean enough power to clear the EN_TERM before the power goes out?

    Yes, this what I meant. Is this possible for your application?

    Best Regards,
    Ethan Galloway

  • 0 in reply to Ethan Galloway
    Prodigy 40 points

    Hi Ethan,

    I did some preliminary test and it worked once. I was not able to make it work again after that, but I was getting a steady 8.33V out of the charger, even with the BMS open. At least it proves the concept. I need to analyze the I2C communication to measure some timing. 

    So, is there any possibility to change some of the default charger register's value set by the TPS25751 chip by modyfing its binary? We have at least 3 registers which gets overwritten each time a cable is inserted and needs the MCU to put them back in their correct state.

    Regards,

    Sébastien

  • +1 in reply to Sebastien Gravel
    TI__Mastermind 35736 points

    Hi Ethan, 

    Sebastien Gravel said:
    So, is there any possibility to change some of the default charger register's value set by the TPS25751 chip by modyfing its binary? We have at least 3 registers which gets overwritten each time a cable is inserted and needs the MCU to put them back in their correct state.

    Unfortunately the TPS25751 configuration is standardized to fit into a broad region of applications and setting EN_TERM along with the termination current limit is a setting that is commonly used by other users. You can configure the charge current or the termination current through the TPS25751 GUI tool. 

    EN_TERM for BQ25756 in register 0x14 is not set by TPS25751 in any fashion, you can use your MCU to modify this register through 4CC command "I2Cw" to instruct TPS25751 to perform an I2C write to BQ25765, details of the command is documented in the TPS25751 Technical Reference Manual. 

    Let us know if you have any further questions or concerns! 

    Thanks and Regards,

    Raymond Lin