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[FAQ] AM6442: question about MCU_OSC0 Start-up

Robert Finger
Genius 17367 points
Part Number: AM6442

Team, 

I have a question about "Figure 7-16. MCU_OSC0 Start-up Time" from the datasheet. Here it looks like that MCU_OSC0 is only allowed to start when VDD_MCU is ramping. In reality the osciallation starts already with VDDS_OSC0, while VDD_MCU is still disabled. 

I assume that this is OK and not causing any problems?! But if this is the case, why is the Start-up Time ts shown relatative to VDD_MCU stable? Shouldn't it be related to VDDS_OSC0 stable?

 

Thanks,
  Robert

  • +1
    TI__Guru 62855 points

    The oscillator is powered from VDDS_OSC0. So it may power-up and begin oscillation as soon as VDDS_OSC0 is applied. However, the oscillator has a few control registers which are powered by the VDD_CORE domain. So there is a chance the oscillator may not start until the VDD_CORE is valid. 

    The supply shown in the upper waveform should be named VDD_CORE rather than VDD_MCU. AM64x does not even have a power rail named VDD_MCU. Therefore, I need to get this figure updated in the datasheet. Thanks for asking the question, which highlighted the error in the figure. 

    Regards,
    Paul