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TPS26750: Schematic review for 240W USB-C sink-only application

Rain Haase
Prodigy 131 points
Part Number: TPS26750
Other Parts Discussed in Thread: PMP41115, , TPD4S480, TVS2200

Tool/software:

Hi,

I hope you all are doing well.

I have created a schematic (attached) for a 240W USB-C sink only application using the TPS26750, and it would be very helpful if someone could review it before I send it off for prototyping to ensure its safety.

It closely follows TPS26750EVM, apart from the bidirectional power switch, which is based on PMP41115 - however, the two are very similar, and I decided to use the PMP41115 bidirectional power switch schematic because it seems to save on board area a little bit. I will be programming the EEPROM with a cheap USB programmer (CH341A-based, a newer PCB variant which outputs the correct voltages) which will both power and program the EEPROM while it is mounted on the PCB - this will be done with only 3.3V signals, however, I am not sure if programming the EEPROM in-circuit will cause any issues since it will also be powering LDO_3V3. It would be great if someone could confirm this with me Slight smile

I would like to be able to use this 240W sink in 'dead battery safe mode' as described in page 11 of the TPS26750EVM user guide, which allows for the core of the TPS26750 to be used without an external supply, as the 3.3V and 1.5V regulators can be powered by a voltage divided VBUS of around 24V max from the TPD4S480 (as far as I'm aware). Is this implementation correct, and is there any special considerations (that is, in programming or hardware) that I have to consider when operating in this mode? Should Q1 be a little bigger to ensure there is not excessive heating?

Also, this is not a very important question for me, but I would like to know - what is the behaviour of TPS26750 when there are no PDOs that match what is requested? Is this something that can be set in the Application Customisation tool? For example, if the required sink power is set to 240W in the USB PD application customisation tool, and the PDOs of the source only go up to 140W, will it let through that 28V or close the power switch?

Thank you so much for your support.

Kind regards,

Rain

240Wsinkschematic.pdf

  • 0
    TI__Genius 13880 points

    Hi Rain,

    I will review your schematic and answer your questions be EOB on Thursday.

    Kind regards,

    Conner 

  • 0 in reply to Conner Gillette
    Prodigy 131 points

    Hi Conner,

    Thank you for letting me know, sounds great Slight smile

    Kind regards,

    Rain

  • 0 in reply to Rain Haase
    TI__Genius 12855 points

    Internal Status: TI will provide an update by EOB Thursday.

  • 0 in reply to Alex Liu
    TI__Genius 13880 points

    I finish this first thing tomorrow Rain. My apologies for the delay.

    Regards,

    Conner

  • 0 in reply to Conner Gillette
    Prodigy 131 points

    Hi Conner,

    That's all good, thanks for your help Slight smile

    Kind regards,

    Rain

  • +1 in reply to Rain Haase
    TI__Genius 13880 points

    Hi Rain,

    I've completed the schematic review. The items in green are good, the items in yellow just mean the values I need to evaluate are off sheet, and red is a needed change.

    In this case, for the capacitance on VPWR of the TPD4S480, I know that you likely used the value from the EVM. This is a mistake that will be corrected for the next revision (Rev A3) of the TPS26750EVM. Therefore the recommendation for you to change the cap on VPWR from 0.1uF to 1uF is not due to any mistake you made, but it does need to be made.

    Regards,

    Conner

    rain_tps26750_sch_review.xlsx

  • 0 in reply to Conner Gillette
    Prodigy 131 points

    Hi Conner,

    Thank you so much for the review - I have attached the updated schematic file. Just to clarify, ADCIN1 and ADCIN2 tied to ground should allow me to operate the device in Dead Battery Safe Mode as described by page 11 of the TPS26750EVM, right? I changed C7 to 1uF as you suggested, too. I am not using this device for any other purpose than a sink, hence why I did not use a resistor divider and instead followed the instructions in 'without using Rup or Rdown' on page 28 of the TPS26750 datasheet.

    Does everything else look good? As far as I'm aware, I should just be able to load the configuration from the USB C Application Customisation tool to the EEPROM using an I2C programmer, then plug it into a USB-C wall adapter without any external power, and the correct voltage and current will be negotiated at the output VBUS.

    Thank you so much for your patience, and detailed response :) I hope you all have a great week. I will click 'resolved my issue' once you respond to this message, just to confirm. 

    240Wsinkupdated.pdf

  • 0 in reply to Conner Gillette
    Prodigy 131 points

    Hi Conner,

    After closer review of the schematic review you provided, I also tied all I2Ct pins and GPIO [0 1, 3, 4, 5, 6, 7, 11] to GND since they are not used.

    I'm also assuming the requirement for a schottky diode and TVS diode on VBUS is removed by the addition of the TPD4S480 protector IC, and/or because I am only using it in sink mode.

    Thanks so much for your clarification.

  • 0 in reply to Rain Haase
    TI__Mastermind 30372 points

    Hi Rain,

    Conner is currently out of office. Please expect some delay in responses. 

    Best Regards, 

    Aya Khedr 

  • 0 in reply to Aya Khedr
    Prodigy 131 points

    Hi Aya,

    That's alright, thanks for letting me know.

    Have a great day!

    Kind regards,

    Rain

  • 0 in reply to Rain Haase
    TI__Mastermind 30372 points

    Hi Rain, 

    No problem! Thank you.

    Best Regards, 

    Aya Khedr

  • +1 in reply to Aya Khedr
    TI__Genius 13880 points

    Hi Rain,

    1. Thank you for the clarification, that's good.

    2. You are correct, the TPD4S480 takes care of the functionality that would be provided by the Schottkey diode and the TVS2200.

    Regards,

    Conner

  • 0 in reply to Conner Gillette
    Prodigy 131 points

    Hi Conner,

    I hope you are doing well.

    Sorry for sending two messages for you to reply to above - I don't think you saw the additional clarifications I would like, and I apologise for not putting that into one paragraph :) As pasted from the message above the one you just responded to, I would just like to clarify one more thing:

    "Should ADCIN1 and ADCIN2 being tied to ground should allow me to operate the device in Dead Battery Safe Mode as described by page 11 of the TPS26750EVM?"

    I know this is already stated in the datasheet, but I would just like to clarify that I am not confused about any smaller details here.

    Thank you so much for your patience - just this one more answer will resolve the question.

    Kind regards,

    Rain

  • 0 in reply to Rain Haase
    TI__Genius 12855 points

    Internal Status: In-Progress - TI to provide analysis and response.

  • +1 in reply to Rain Haase
    TI__Genius 13880 points

    I am well Rain, thank you for asking. I hope you're doing well too. 

    Yes, you are exactly correct. If you tie ADCIN1 and ADCIN2 to ground, and plug a USB-C/USB-PD source into the port of your device that has the TPS26750  (while your device is unpowered), you would be testing the device in DeadBattery mode, and the mode your device would be set to when in the DeadBattery state would be Safe Mode.

    Let me know if you have any other questions or if I can be of any further assistance, and I'll be happy to help.

    Kind regards,

    Conner

  • 0 in reply to Conner Gillette
    Prodigy 131 points

    Hi Conner,

    Thank you so much for supporting me with the development of this board. That was the last question I had for this topic, so I clicked 'this resolved my issue'. Have a great day!

    Kind regards,

    Rain