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TPS26750: Using TPS26750 as a USB PD Trigger controlled by an MCU

Richard Axelsson
Prodigy 105 points
Part Number: TPS26750

Tool/software:

We will use USB PD as an adjustable power supply, up to 240W, i.e. sink only.

Basically this is what we want to do.

1. Read source capability, store in MCU

2. MCU will continuously request voltage and current based on capability. Can be fixed, PPS or AVS.

It would seem quite straight forward, but I do have some questions.

1. Do I use "Dead Battery Configuration" AlwaysEnableSink or SafeMode? From datasheet table 7-6 it seems like I should use AlwaysEnableSink when using an external MCU.

2. I will not need a EEPROM, I will upload configuration from the MCU through I2Ct at boot, it is possible from what I understand? I am a bit confused about the address, datasheet 7.3.11.1.2 said "once the boot process is complete, the port has a unique address set by ADC", is there a different address to send configuration?

3. Do I need to connect the I2Cc from TPS26750 to the MCU, if so why? I see it is connected in the evaluation board.

4. I will read/write registers through I2Ct at the address set by ADC, correct?

5. In order to read USB PD source capability, all I have to do is to read register 30h, or do I first have to send GSrC?

6. In order to change the desired voltage/current, all I have to do is to write to register 37h?

Thanks,

/Richard

  • 0
    TI__Mastermind 29852 points

    Hi Richard, 

    Thank you for reaching out!

    I will review and get back to you with feedback early next week.

    Best Regards,

    Aya Khedr

  • 0 in reply to Aya Khedr
    Prodigy 105 points

    Thanks.

    Any news?

  • +1 in reply to Richard Axelsson
    TI__Mastermind 29852 points

    Hi Richard, 

    See my responses below: 

    Richard Axelsson said:
    1. Do I use "Dead Battery Configuration" AlwaysEnableSink or SafeMode? From datasheet table 7-6 it seems like I should use AlwaysEnableSink when using an external MCU.

    Your understanding is correct, AlwaysEnableSink is required to enable the sink path to provide power to the system while loading the patch bundle over I2Ct via MCU. 

    Richard Axelsson said:
    2. I will not need a EEPROM, I will upload configuration from the MCU through I2Ct at boot, it is possible from what I understand? I am a bit confused about the address, datasheet 7.3.11.1.2 said "once the boot process is complete, the port has a unique address set by ADC", is there a different address to send configuration?

    In this section, the boot process refers to the device booting from ROM, in which it will have limited functionality in preparation to receiving the patch bundle that can be pushed via MCU over I2Ct. 

    Richard Axelsson said:
    3. Do I need to connect the I2Cc from TPS26750 to the MCU, if so why? I see it is connected in the evaluation board.

    No, you do not need to connect I2Cc to the MCU. The EVM utilizes the TIVA MCU to communicate with the online GUI Tool, specifically for flashing a binary file onto the on-board EEPROM and is only intended for EVM use. 

    Richard Axelsson said:
    4. I will read/write registers through I2Ct at the address set by ADC, correct?

    Correct. 

    Richard Axelsson said:
    5. In order to read USB PD source capability, all I have to do is to read register 30h, or do I first have to send GSrC?

    Register 30h will store the latest Source Capabilities message received. GSrC is used to send a "Get Source Capabilities" message to the Source at any time if desired. Register 30h will update and store the message received.

    Richard Axelsson said:

    6. In order to change the desired voltage/current, all I have to do is to write to register 37h?

    That is correct. Ensure that EPR AVS Enable Sink Mode [128] is set to 1. The MCU can then update the AVS Output Voltage and AVS Operating Current as desired. 

    Please let me know if you have additional questions. 

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Prodigy 105 points

    Hi, some follow up questions.

    1. Do I need to set the Transmit Sink Capability Register, or can I just leave that? What is the difference between Variable vs Sink PPS/AVS?

    2. I cannot find a good specification of how to translate Receive Source Capability Register, other than the USBCPD Application Customization Tool TX Sink Capabilities, is there a good overview you could guide me to? 

    3. If the source is non PPS/AVS, how do I set the voltage? Do I still just set PPS/AVS to eg. 9V/48V? I cannot find anywhere where I would request a specific PDO profile.

  • +1 in reply to Richard Axelsson
    TI__Mastermind 29852 points

    Hi Richard, 

    Richard Axelsson said:
    1. Do I need to set the Transmit Sink Capability Register, or can I just leave that? What is the difference between Variable vs Sink PPS/AVS?

    Yes, the Transmit Sink Capability Register should be set. The difference between these power supplies is defined in the USB PD Specification (see below):

    Richard Axelsson said:
    2. I cannot find a good specification of how to translate Receive Source Capability Register, other than the USBCPD Application Customization Tool TX Sink Capabilities, is there a good overview you could guide me to? 

    The Source Capabilities Message structure is defined in the USB PD Specification as well. 

    Richard Axelsson said:
    3. If the source is non PPS/AVS, how do I set the voltage? Do I still just set PPS/AVS to eg. 9V/48V? I cannot find anywhere where I would request a specific PDO profile.

     

    The voltage/current levels along with the type of power supply supported should be set in Transmit Sink Capabilities Register.

    Best Regards, 

    Aya Khedr

  • 0 in reply to Aya Khedr
    Prodigy 105 points

    Thanks,

    Is there any way to detect if an e-marker cable is being connected? I cannot find anything in the docs.

  • 0 in reply to Richard Axelsson
    TI__Mastermind 29852 points

    Hi Richard, 

    Please post a new thread for the E-marked cable topic for better trackability. 

    Thank you in advance!

    Best Regards, 

    Aya Khedr