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AM3874 Power-up & Power-down

Marcos Lopez Cuevas
Expert 4175 points

Other Parts Discussed in Thread: AM3874

Hi team,

my asigned account Unidesa (40K units/year) is configuring their power supply to satisfy the power up/down sequence of the AM3874/DM8127 just reading the datasheet but looking at the pictures taken just using the Mistral EVM (attached to this post) we have doubts on it:

What is better to do: slow discharge when power down or better a capacitor's active discharge by the power supply? second option is quicker than first one and doesnt depend on each rail load.

The pictures attached to this post were taken in order to observe the sequence but is quite caotic as you can see, seems it doesnt satisfy the DS requirements at all.

that's the signals adquired: CH1 1V8, CH2 3V3, CH3 1V5, CH4 1V1 Abajo: CH1 1V8, CH2 3V3, CH3 1V5, CH4 POR (Power On Reset)

During 150 ms its really random and after this seems to sastify a passive discharge?

just tell me if you need more details, thanks in advance for your support!

Centaurus EVM powerup down sequence.docx
  • 0
    TI__Guru**** 393215 points
    Hi Marcos,
     
    The relevant section is AM387X Datasheet, section 7.2.8.2. The important factors are listed as notes below Table 7-7:
     
    1. CVDD, CVDD_x must go down first.
    2. DVDD_DDR must go down second.
    3. 3.3V supplies must go down third.
    4. 1.8V supplies must go down last.
     
    At all times during power-down the 1.8V supplies must be greater or equal to the CVDD, CVDD_x and DVDD_DDR supplies.
    At all times during power-down the 3.3V must be less than 2V higher than the 1.8V supplies.
     
    There are no strict timing restrictions for power-down. There is also an Errata on power sequencing, which I'm attaching here: 8311.Power Supply Sequence Errata rev a- ARM BU.pdf