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AM4377: Discrete power solution power-down sequencing

shigehiro tsuda
Mastermind 9490 points
Part Number: AM4377


Hi,

Our customer is trying to design the circuit of the AM4377 power supply in discrete power configuration.
We refer to the following documents.

Discrete Power Solution for AM437x:
www.tij.co.jp/.../slvuab1.pdf

Figure 8. Power-Off Sequence with All Power Supply Rails in this document has the power down sequence measurement results.

I think that it does not comply with the following specifications of datasheet, is this figure or Figure 3. Powering and Sequencing Circuit for AM437x Requirements correct?

5.13.1.3 Power-Down Sequencing
The preferred way to sequence power down is to have all the power supply ramped down sequentially in
the exact reverse order of the power-up sequencing.

Best Regards,
Shigehiro Tsuda

  • 0
    TI__Guru**** 393215 points
    Hi,

    The same section you quote from also says:

    "When using simplified power-down sequence, there are no power-down requirements between the VDDS, VDDS_CLKOUT and VDDSHVx [x=1-11] supplies and are ramped down together without any reliability concerns."
  • 0 in reply to Biser Gatchev-XID
    Mastermind 9490 points

    Hi Biser,

    Thank you for quick reply.

    When using simplified power-down sequence, I understood that there is no power supply sequence between VDDS, VDDS_CLKOUT and VDDSHVx.
    Is it correct that these sequences are not required for these power supplies and VDD_MPU(1.1V),VDD_CORE(1.1V),VDD_DDR(1.5V), 1.8V and 3.3V other than the above.
    Since it is the reverse of Power up, I think that it is the sequence of ①, but in "Figure 8 Power-Off Sequence with All Power Supply Rails", it seems to be turning down in the sequence of ②.
    ① 1.1 V -> 1.5 V -> 1.8 V -> 3.3 V
    ② 3.3 V -> 1.8 V -> 1.5 V -> 1.1 V

    Best Regards,
    Shigehiro Tsuda

  • 0 in reply to shigehiro tsuda
    TI__Genius 13567 points

    Hello Shigehiro,

    For the intent of this app note Figure 8 is a "simultaneous" power down. It may appear to have the order of sequence ② but since we are using RC delays affected by temperature and there will be variations in input EN thresholds for these parts the actual ordering is variable. The power down is close enough that we call it simultaneous. The ACTUAL requirement is that the rails power must power down after PORz.

  • 0 in reply to Ahmad_Rashed
    Mastermind 9490 points

    Hi Ahmad,

    Thank you for quick reply.
    I understood  the intent of this app note Figure 8 by your explanation.

    Best Regards,
    Shigehiro Tsuda