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Question of Power-Down Sequencing on AM335x.

RY9983
Guru 10570 points
Other Parts Discussed in Thread: TPS65910A

Hello.

I have a question about AM335x power-down sequencing.
I have refered Datasheet.

sprs717d: (P96) 4.1.2
Further, it should also be ensured that the VDDS supply should be ≥1.5 V of all the other supplies in the system during the ramp down.

I can not understand this meaning.

- What do you specified about "of all the other supplies in the system" ?

- What do you specified about "during the ramp down" ?

Best regards,
RY

  • 0
    TI__Guru**** 393215 points
    Hi RY,
     
    Are you using a TI recommended PMIC? If you do, then no need to worry about ramp-down. If you don't, it's up to you to follow the Datasheet recommendations. "All the other supplies" refers to all processor supplies.
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 10570 points

    Hello, Biser.

    Thank you so much for your quick answer.
    We are under considering about using TI's PMIC.

    Sorry, can I confirm detail about your comment?
    I think Datasheet description is as below.

    The VDDS supply need to be ≥1.5V until all other processor supplies are powered down.
    When it is desired to ramp down VDDS and VDDSHVx[1-6] simultaneously, it is no problem if the defference between VDDS and VDDSHV[1-6] during the entire power-down sequence is <2V.

    Is it right?

    Best regards,
    RY

  • 0 in reply to RY9983
    TI__Guru**** 393215 points
    Hi RY,
     
    The VDDS supply needs to be at least 1.5V greater than all other processor supplies, and less than 2V greater than VDDSHVx[1-6] during power down.
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 10570 points

    Hello, Biser.

    Thank you for helping me.

    Your advice regarding the VDDS supply needs to be:
     1. At least 1.5V greater than all other processor supplies
     2. Less than 2V
     3. Greater than VDDSHVx[1-6] during power down.

    Right?

    Is No2 restriction for Absolute maximum ratings?

    Best regards,
    RY

  • 0 in reply to RY9983
    TI__Guru**** 393215 points
    Hi RY,
     
    1. is correct.
    2. and 3. should be combined, i.e. VDDS should follow VDDSHVx[1-6], difference VDDS - VDDSHVx[1-6] should be less than 2V during power-down.
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 10570 points

    Thank you so much, Biser.
    I understand !

    Best regards,
    RY

     

  • 0 in reply to RY9983
    Guru 10570 points

    Hello, Biser.

    Sorry, can I have a once more question about power down description?

    The description is:
     - It should be ensured that the VDDS supply should be ≧1.5 V of all the other supplies in the system during ramp down.

    My question is:
      When I need to power down VDDS and VDDSHVx [1-6] simultaneously,
      how long do I need to keep up ≧1.5V on VDDS?

    I think there is some rules. for example:
     - VDDS should be ensured ≧1.5V until all 3.3V falls under xxV.
     - Or, it should be ensured until all 1.1V falls under xxV. etc..

    Thank you in advance.
    Best regards,
    RY

  • 0 in reply to RY9983
    TI__Guru**** 393215 points

    Hi RY,

    Here are some comments from our PMIC expert. Case discussed is 1.8 V VDDS and 3.3 V VDDSHVx rails during power down on the EVM. Although TPS65910A does not support power down sequencing, 1.8 V VDDS is assigned to VDAC LDO, which has characteristics to go down after all the other power rails on the PMIC. VDDS 1.8 V rail goes down after 3.3 V rails and the voltage difference between 1.8 V rail and 3.3 V rails is always less than 2 V during power down as defined in AM335x power down sequencing requirements in the datasheet. So, the power down requirements should be satisfied by TPS65910A unless customers have a large loading on 3.3 V rails which makes 3.3 V rail ramp down very slow compared to 1.8 V rails. 

    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 10570 points

    Hello, Biser.

    Thank you very much for forwarding advice from PMIC expert.

    Biser Gatchev-XID said:
    Although TPS65910A does not support power down sequencing, 1.8 V VDDS is assigned to VDAC LDO, which has characteristics to go down after all the other power rails on the PMIC.

    It is good news.
    But, I also have searched about power down sequence of PMIC, It can not be found.
    So, I am not able to represent to end-user that the PMIC is safety.

     - If using TPS65910A, does the power down sequence be satisfied at any time? (e.g. When the souce of power is shut down for electric outage etc..)

     - Can you provide me any description that the characteristics can be satisfied ?

     - And, I think the spec of power down sequence regarding VDDS is not clear for safety designing.
    Is it really not exist ?

    Sorry to trouble you.
    Best regards,
    RY

     

  • 0 in reply to RY9983
    TI__Guru**** 393215 points
    Hi RY,
     
    These last questions should be posted in the Power Management PMIC forum (http://e2e.ti.com/support/power_management/pmu/f/43.aspx). Their experts can surely answer you more accurately.
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 10570 points

    Hello, Biser.

    OK.
    I appreciate your answers.
    How about the below question?

     - And, I think the spec of power down sequence regarding VDDS is not clear for safety designing.
    Is it really not exist ?

    Best regards,
    RY

  • 0 in reply to RY9983
    TI__Guru**** 393215 points

    Hi RY,

    If you read the important notice on the AM335X Datasheet, it says that:

    "Buyer acknowledges and agrees that it is solely responsible for compliance with all legal, regulatory and safety-related requirements concerning its products, and any use of TI components in its applications, notwithstanding any applications-related information or support that may be provided by TI. Buyer represents and agrees that it has all the necessary expertise to create and implement safeguards which anticipate dangerous consequences of failures, monitor failures and their consequences, lessen the likelihood of failures that might cause harm and take appropriate remedial actions. Buyer will fully indemnify TI and its representatives against any damages arising out of the use of any TI components in safety-critical applications."
     
    Best Regards
    Biser

  • 0 in reply to Biser Gatchev-XID
    Guru 10570 points

    Biser.

    Thank you so much for your many advices.
    I accept your answers.
    I am very sorry to trouble you and thanks again.

    Best regards,
    RY

  • 0 in reply to RY9983
    TI__Guru**** 393215 points
    RY, you are not troubling me. We try to answer as best we can on the forums, but we really can not give advice on safety-related issues without having the complete background. I suggest that you contact your local TI FAE or representative and ask for support on this type of issues.
     
    Best Regards
    Biser
  • 0 in reply to Biser Gatchev-XID
    Guru 10570 points

    Hello, Biser.
    Thank you so much for your kind support.
    My question was solved by support of local TI FAE.

    Best regards,
    RY