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BQ25756: BQ25756 + TPS26750 (PMP41115): How to configure USBCPD Application Customization Tool so VREV_ACC >5 V in Reverse Mode (e.g. 24 V)?

Part Number: BQ25756
Other Parts Discussed in Thread: PMP41115, , TPS26750, TPS25750

Tool/software:

Hello TI Team,

System description:

  • Design based on PMP41115 (USB-C PD3.1, up to 240 W), combining BQ25756 (buck-boost bidirectional charger) and TPS26750 (eFuse/ERP power path).

  • PD controller configured with USBCPD Application Customization Tool, image loaded to external EEPROM.

  • Goal: when the BQ25756 enters Reverse/OTG mode, the VREV_ACC (reverse adapter voltage) should be set above the default 5 V, for example 24 V (or according to the PD contract).

 

Current behavior:

  • With battery input (~33 V), the BQ25756 Reverse Mode does activate.

Questions:

  1. Which parameter in the USBCPD Application Customization Tool should be changed so that the BQ25756 targets a reverse voltage >5 V (e.g. 24 V)? In the datasheet this seems to correspond to the VAC_REV register of the BQ25756.

Hardware / test conditions:

  • Battery input: ~33 V.

  • Reverse mode confirmed active.

  • TPS25750 boots from EEPROM with an image generated by the Tool.

  • I will attach screenshots of my basic configuration.

For your reference, I am attaching:

  • The configuration exported from USBCPD_Application_Customization_Tool v1.1.0

Thank you in advance for your support.

  • Hi Raymundo, 

    Thank you for reaching out!

    Goal: when the BQ25756 enters Reverse/OTG mode, the VREV_ACC (reverse adapter voltage) should be set above the default 5 V, for example 24 V (or according to the PD contract)

    The TPS26750 will configure the BQ25756 VAC_REV based on the PD contract negotiated. The desired PDOs (power data objects) are set based on Q2 Maximum Sourcing Power. Currently this is set to 100W in your configuration file which sets the maximum PDO to 20V/5A. 

    For >100W PDO, I recommend selecting the 140W power level in the question. Then, you could manually input the desired voltage/current level in the Transmit Source Capabilities Register 0x32.

    See Section 3.4.4 in the EVM User Guide on how to enable Advanced Mode to configure additional fields. 

    Please let me know if you have additional questions/concerns. 

    Best Regards, 

    Aya Khedr

  • With the basic configuration I showed earlier, whenever I disconnect the USB Type-C, I manage to have 5V at the PPHV node, which is the default voltage. So, I want to know how to raise that default 5V to, for example, 24V.

    I’m not referring to having that 24V present when the USB Type-C is connected, but rather when it is disconnected—in other words, using the BQ25756’s Reverse mode. I want it to use the battery pack voltage to obtain that 24V in PPHV node. I want to know the exact parameter I need to modify in the advanced configuration to change that. Please.

    In the answer you gave me, the entry for the 0x32 register has the "Voltage" setting locked in a value range from 0 to 5V and is set to 5V by default, with no possibility of changing it, so I cannot modify it. Is it locked because of a different setting that has to be modified elsewhere or what is the limitation?



  • Hi Raymundo, 

    Could you elaborate further on why there is a need for 24V on PPHV when the Type-C cable is disconnected? 

    This violates the PD specification, because upon an implicit contract (initial Type-C connection), a maximum of 5V can be present on VBUS. Once the PD negotiates with the port partner, and 24V (EPR) for example is supported on both sides, then 24V can be present on PPHV --> VBUS. 

    Best Regards, 

    Aya Khedr

  • It is the need of our application, one thing is to provide 20V through the PD when the Type-C is plugged. In this case, that voltage is used both to power the board/device and charge the batteries. But whenever the Type-C is disconnected, the PD should not limit to 5V the entire rail.

    We are working in conjunction with a BQ25756 which switches to reverse mode once the Type-C is unplugged. In this case, the system lets the batteries power the board/device, and we need to have more than 5V present in the PPHV net.

    We have already tested this behavior externally setting up the BQ25756 through a ESP32 (bypassing the EEPROM) and configuring the registers manually (VAC_REV), so we know it is possible.



  • Hi Raymundo, 

    Thank you for clarifying.

    I will need to look into this further and get back to you with feedback. 

    Best Regards, 

    Aya Khedr

  • Ok, I await your response, Thank You.

  • No problem. I will get back to you by Thursday. 

    Best Regards, 

    Aya Khedr