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AM3358: Additional condition of Power-Supply Sequencing

shigehiro tsuda
Mastermind 9490 points
Part Number: AM3358

Hi,

Please tell me the reason why the following sequence was added by rev.K in the AM335x datasheet.
What will happen if this sequence is not followed?

Example)
Device breaks
Device does not start up

Figure 6-2. Preferred Power-Supply Sequencing With Dual-Voltage I/Os Configured as 3.3 V

G. If all the 1.8-V supplies are not sourced from the same power supply, it is required to power up VDDS before other
1.8-V supplies. Further, it is also recommended to source VDDS and VDDSHvx [x = 1-6] when configured as 1.8V
from the same power supply.

Best Regards,
Shigehiro Tsuda

  • 0
    TI__Guru 62855 points
    The note was added to provide clarity of dual-voltage IO power supply connectivity requirements when a system has multiple 1.8v power supplies.

    Power supply sequence diagrams in the data sheet have always showed the requirement of 1.8V before 3.3V, which defines the requirement when dual-voltage IOs operate at 3.3V. The diagrams also showed all 1.8V supplies ramping at the same time which may not be the case in a system with multiple 1.8V supplies. Therefore, the data sheet did not address the case where a system has multiple 1.8V supplies that do not ramp at the same time.

    The new note explains the requirement that VDDS is present before any of the other 1.8V supplies, and the recommendation where the VDDS and VDDSHV supply pins of dual-voltage IOs should be connected to the same 1.8V source.

    The device may experience functional and reliability issues if the expected power sequence is not followed.

    Regards,
    Paul
  • 0 in reply to peaves
    Mastermind 9490 points

    Hi Paul,

    Thank you for quick reply.

    Is it difficult to answer the followings?
    If additional sequences were not followed, a problem occurred, so it was added to the datasheet.
    I have to explain to our customers, so I would like information on the added reasons.
    Even if it does not protect it, there is not a problem in particular, but it was added because it may cause a problem?

    Best regards,
    Shigehiro Tsuda

  • 0 in reply to shigehiro tsuda
    TI__Guru 62855 points

    A few customers implementing a PMIC solution with multiple 1.8V outputs have ask about sequencing requirements of the 1.8V supplies. These inquiries highlighted the lack of clarity provided by the new note. So the note was added to proactively answer questions related to power sequencing requirements of the 1.8V supplies.

     

    We are not aware of any issue caused by improper sequencing of the 1.8V supplies. However, there are many variables that may contribute to potential problems resulting from improper power sequencing. Therefore, it is not possible to guarantee a system will not have a problem if a product is not designed to follow the requirements/recommendations described in the note.

     

    Regards,

    Paul

  • 0 in reply to peaves
    Mastermind 9490 points

    Hi Paul,

    Thank you for quick reply.

    What we are worried about is correspondence to customers who have not already had this information and have already been designed.
    Since this information was added in the recent datasheet, there is a possibility that there are many customers who are finished the design without observing this information and many are getting into the market as products.
    We are concerned about the influence on these customers.

    Do they need to fix it?
    or
    Since problems do not occur in particular, do they not have to fix it?

    Best Regards,
    Shigehiro Tsuda

  • 0 in reply to shigehiro tsuda
    TI__Guru 62855 points

    Customers need to follow the requirement/recommendation described in the note to avoid potential functional and/or reliability issues.

    Regards,

    Paul

  • 0 in reply to peaves
    Mastermind 9490 points
    Hi Paul,

    Thank you for various support.
    It is difficult to fix hardware after completion of development by customer, so I will confirm with local TI FAE about future correspondence.

    Best Regards,
    Shigehiro Tsuda