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DRA821U: Pre Schematic Checklist Questions

Calex36
Intellectual 2455 points

Part Number: DRA821U
Other Parts Discussed in Thread: DRA821

Hi, 

I have been looking into the details for the evaluation kit schematics for the DRA821, and I have a few questions:

 

  1. I see that there is used an external RTC clock circuit on the “common processor board”. Is there any specific reason why the RTC that is built into the PMIC TPS6594xxxx is not used?
  2. I observe that the VBACKUP pin on that PMIC is connected to ground. Both coin cells and supercaps is mentioned. If a supercap is used, is that charged via the VBACKUP pin? And are there anything that will have to be configured when either using a coin cell or a supercap?
  3. I assume that it would be possible to use an external 32.768kHz LVCMOS clock oscillator powered from the VOUT_LDOVRTC output on the PMIC A?
  4. I’m at a stage where I have to start doing assessment for the current consumtion in my design. You typically provide a spreadsheet to aid that? Or, do you have any actual measurement results from the EVM?
  5. I see in the schematics for the SOM, PMIC B, page 23, that it is mentioned that the I2C address is programmed in the NVM. Is the configuration of the NVM, including the I2C addresses something that comes preprogrammed from you or is that something I would have to do at my side? Is the NVM something that can be changed after it has been programmed?
  6. In the schematics for the SOM, PMIC A, page 22, GPIO9, there is mentioned an Errata. This does not seem to be availeble, and is this something I have to consider?

Any feedback you can provid here is much appreciated 

Many Thanks 

  • +1
    TI__Guru 57215 points

    Regarding #1 - depending on the required features for RTC, and can chose to use either PMIC or external RTC.  If the PMIC functionality meets your requirements, no need for external RTC.

    Regarding #4 - TI does have power estimation spreadsheets (currently only internal use).  Contact your TI Program Manager or FAE to submit a power estimation request for your design.

    Regarding #5 - Yes, PMIC is pre-programmed - including I2C assignments, default voltage assignments, and up/down power sequences. 

    Regarding #6 - Based on the PMIC part number you order, it will likely have the errata item fixed.  Note the DRA821 Power solution selections/diagrams should be updated with latest PMIC part numbers (which included errata fix)

    I'm requesting help with other items

  • +1
    TI__Guru 74181 points
    Calex36 said:
    I observe that the VBACKUP pin on that PMIC is connected to ground. Both coin cells and supercaps is mentioned. If a supercap is used, is that charged via the VBACKUP pin? And are there anything that will have to be configured when either using a coin cell or a supercap?

    Yes, it is charged via the VBACKUP pin.  The configuration settings are described in 8.15 of the datasheet.

    https://www.ti.com/lit/ds/symlink/tps6594-q1.pdf#page=37

    https://www.ti.com/lit/ds/symlink/tps6594-q1.pdf#page=69

    https://www.ti.com/lit/ds/symlink/tps6594-q1.pdf#page=276

    Calex36 said:
    I assume that it would be possible to use an external 32.768kHz LVCMOS clock oscillator powered from the VOUT_LDOVRTC output on the PMIC A?

    The VOUT_LDOVRTC is not intended for external loading.  This is intended for the internal RTC within the PMIC.

    https://www.ti.com/lit/ds/symlink/tps6594-q1.pdf#page=6

    Regards,

    Chris

  • 0 in reply to Chris Sterzik
    TI__Intellectual 2455 points

    #2, What is the default configuration for the VBACKUP pin in this application. With or without charging?

     

    #3, the oscillator I intend to use typically draws about 1uA, and I would assume that the VOUT_LDOVRTC would be able to source that much?

    #3, Is it at all possible to use an external LVCMOS oscillator to drive the clock in?

  • 0 in reply to Calex36
    TI__Guru 74181 points

    Hello,

    Calex36 said:
    What is the default configuration for the VBACKUP pin in this application. With or without charging?

    BB_CHARGER_EN = 0 by default, this means without charging. https://www.ti.com/lit/ds/symlink/tps6594-q1.pdf#page=276

    Calex36 said:
    the oscillator I intend to use typically draws about 1uA, and I would assume that the VOUT_LDOVRTC would be able to source that much?

    I cannot advocate a use case which is in contradiction to the datasheet.  You would need to validate that the RTC voltage domain and associated functions are not impacted by the external load or noise coupled in through the connection to the load.

    Calex36 said:
    Is it at all possible to use an external LVCMOS oscillator to drive the clock in?

    I do not believe so, but I have not attempted.  There is no bypass mode designed to support a digital input. 

    Regards,

    Chris