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USB-PD-CHG-EVM-01: Design to charge either 3.7V or 12V, using USB-C or additional 12V input

Douglas Ross
Prodigy 105 points
Part Number: USB-PD-CHG-EVM-01
Other Parts Discussed in Thread: TPS25750, BQ25792

Good day, 

We have the requirements to power a device using either 12V DC input, or USB-C PD. It should also be able to charge either a 12V battery or a 3.7V battery, depending on the setup. 

I understand that you can program the TPS25750 using the GUI to use the corresponding charger and change the battery output voltage to either 12V or 3.7V.

1. Is this info then stored on the EEPROM? And every time the USB-C is plugged in, this will communicate the setup to the BQ25792 using I2C?

The BQ25792 can accept two power sources. If the battery is removed and the device shipped. Then the battery is replaced and the device is powered on using the 12V input to the additional input on the BQ25792.

2. How will the BQ25792 determine what charging profile to use if the USB-C haven't powered the TPS25750 to configure the BQ25792? 

Would this approach work if I have a buck-boost converter on the Vsys Line of the BQ25792 to convert the 12V or 3.7V to 5V output? If not, any suggestions on how I can approach this more efficiently?

Regards

Douglas

  • 0
    TI__Guru**** 167196 points

    Hi Doug,

    Regarding 1, the info is stored in TPS25750 memory (not sure if its EEPROM) and communicated at power up.

    Regarding 2, the BQ25792 default charge voltage and current configuration is set by the PROG pin resistor at charger power up (battery attached or input power applied).  The TPS25750 firmware can rewrite those settings when it powers up.   

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 105 points

    Hi thank you. 

    So the flash IC on the eval kit isn't necessary? 

    If the prog is the default, then we would require a different resistor for the two different battery options. I believe we might be able to do this by using jumpers to select the different battery option. 

    And just to make sure, if a non PD usb-c is connected, the 5V would still be boosted by the BQ25792 to 12V if needed, it will just not be able to provide enough current to charge the battery and run the system. What will the state of the STAT pin be if this happens? I assume low, because it might charge a little bit? Or will it be flashing to indicate a fault?

  • 0 in reply to Douglas Ross
    TI__Guru**** 167196 points

    Hi Douglas,

    The flash is necessary for full functionality.  The BQ25792 PROG pin resistor sets default fsw, charge voltage (and minimum SYS voltage) and charge current and ILIM_HIZ pin sets default input current limit.  STAT is low if charge current is flowing and no faults.  STAT flashes if there is a fault.  If non-USB C 5V bypasses the PD controller and gets to the BQ25792, then it will start up and provide at least the minimum system voltage at SYS.  If you want to use the charger's D+/D- for a legacy USB 5V supply, that input must be VAC1. 

    I am going to move this to the PD controller team in case they have any suggestions.  I will still be copied on replies.

    Regards,

    Jeff  

  • +1 in reply to Jeff F
    TI__Genius 13880 points

    1. Yes, the configuration you create on the TPS25750 Application Customization GUI can be saved as a binary and written to an EEPROM. The TPS25750 then, at boot, reads the configuration from the EEPROM. There is also the option to use an external controller to send the configuration to the TPS25750, however using EEPROM is simpler to implement.

    The TPS25750 communicates the desired BQ settings to the BQ25792 upon power-up, correct. It also sends updated BQ settings via I2C depending on the PDO negotiated with the port partner.

    A Type-C contract would still provide 5V, and the current is dependent on the Rp value (as detailed in the Type-C spec).

    Kind regards,

    Conner Gillette