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Original question:

TPS65987D: Power and Current Limiting questions

TPS65987D: Schematic/Design questions

Brian Angiel
Expert 4070 points
Part Number: TPS65987D
Other Parts Discussed in Thread: TPS65987, TPD6S300

I have a few more questions, related to my previous post, as I wrap up the schematic design:

  1. Can the SPI flash memory be programmed through the PD controller's I2C interface? The question relates to both the manufacturing process, as the flash memory may be programmed as part of the build process, as well as to the ability to update the flash later, in case the PD configuration needs to be modified.  I would like to know if exposing the I2C interface is sufficient from a manufacturing test and programming standpoint, or if I will also need access to the SPI interface to access the memory directly.  
    1. If the SPI interface is needed, are there any issues with tapping into the SPI while it is connected to the TPS65987D and powered?
  2. {Re: Section 3.5 Global System Configuration} I saw in the Host Interface TRM that the SPI flash can be set as read only or updatable in the TPS65987 global system configuration settings.  Is that the main control setting for the flash memory from a write standpoint?  I am curious about the security implications of being able to update the flash memory, and that is the only control I have found. Please elaborate on any other security provisions between the PD controller and flash memory in terms of being able to update the contents later (either in manufacturing or in the field).
  3. The maximum external load on TPS65987D's LDO_3V3 is specified at 25mA and the Winbond W25Q80DVSNIG can pull up to 25mA during write operations. The LDO is also powering TPD6S300 on LDO_3V3 (max current drain of 0.135mA). Would it be best to add another power source to the design?
  4. Are there any GPIOs for TPS65987D that you recommend making available for debug, programming or other purposes for this application?

Thanks, team.

Brian Angiel

  • 0
    TI__Mastermind 36756 points
    Hi Brian,

    1. The first time the boards are programmed will have to be through the SPI interface. Once their is a valid image on the SPI flash, the device can bootup and subsequent updated can be done through the I2C interface.
    2. The FLxx commands can be used to update the SPI flash in the field through the I2C interface. if you enable the "SPI Read Only" bit, these commands cannot update the flash. The following app note highlights how the SPI flash can be updated over I2C: www.ti.com/.../slvae21.pdf
    3. No, the 3.3V LDO is specifically designed for powering the external SPI Flash. Current pulses over 25mA can be okay. However, DC current on LDO_3V3 should be under 25mA.
    4. All of the GPIOs are configurable. It may be helpful to have a few going to test points for debug purposes.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,
    Eric
  • 0 in reply to Eric Beljaars
    TI__Expert 4070 points
    Thanks, Eric. Could I share my current schematic with you offline for review?
  • 0 in reply to Brian Angiel
    TI__Mastermind 36756 points

    Hi Brian,

    We typically do not complete schematic reviews unless there is an urgent need. I would suggest cross referencing the TPS65987-90EVM and also TPS65988EVM. Additionally, we created a hardware design guide app note that highlights what should be connected to each pin:

    If this answers your question, PLEASE select This resolved my issue

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    TI__Expert 4070 points
    Hi Eric,

    I've had an opportunity to run through that document. Thank you. Quick follow up question:
    What do I do with an unused PP1_CABLE pin (25)? Ground it, float it? Something else? I couldn't find anything conclusive so any input you have here is appreciated.

    Thanks
    Brian
  • 0 in reply to Brian Angiel
    TI__Mastermind 36756 points

    Hi Brian,

    PP_Cable must be connected to 3.3V or 5V if any alternate mode is to be supported on the Type-C Cable. It is also needed if you need a 5A contract. Some Type-C Cables have an e-marker inside of them that are powered by VCONN. PP_Cable is the system side of the VCONN FET. The PD controller gets information of the cables capabilities through the e-marker. This would be unavailable to you if PP_Cable was grounded. I would suggest tying it to an existing 3.3V or 5V rail in your system so that you do not lose this additional functionality.

    If this answers your question, PLEASE select This resolved my issue

    Thank you,
    Eric

  • 0 in reply to Eric Beljaars
    TI__Expert 4070 points
    Can it be tied to the LDO_3V3 output generated by TPS65987D, or would that start to stress the pin too much with the pullups, Flash, TPD6S300 and PP1_CABLE pin?
  • 0 in reply to Brian Angiel
    TI__Mastermind 36756 points
    Hi Brian,

    I would not recommend tying PP_Cable to LDO_3V3 as VCONN can source up to 600mA in some cases. LDO_3V3 would not be a sufficient supply.

    Thank you,
    Eric