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Power-up sequence problem on DM648

vcar4195
Intellectual 285 points


There is a power-up sequence problem about DM648. As mentioned in datasheet, the power-up sequence should be 3.3V --> 1.8V --> 1.2V, meaning 3.3V should be supplied before 1.8V and 1.8V should be supplied before 1.2V. While this is different from other Davinci DSP families like DM6446 and DM6467. The power-up sequence of the DSPs are commonly 1.2V --> 1.8V --> 3.3V.
As DM648 are one of the Davinci series DSP, the power-up seqence should have the same mechanism as other DSPs do. Therefore is '3.3V --> 1.8V --> 1.2V' power-up sequence right on DM648? And can anyone tell me the reason why DM648 has the reverse power-up sequence compared with other DSP series?
  • TI__Mastermind 41665 points

    Different devices will often have different power supply sequencing requirements depending on how the internals of the device were designed to be brought up, in the case of the DM644x the core is to be brought up before the i/o however in the DM648 case as you have found the i/o is to be brought up before the core. These are simply two different devices, though they are both Davinci branded internally they are entirely different, one of the main differences being that the DM644x devices have an ARM core whereas the DM648 is DSP only part.

    The sequence for the DM648 as written in the datasheet is correct, and makes sense if compared to some other DSP only devices. For example a better Davinci device to compare the DM648 to from a power sequencing standpoint is the DM6437, which shares the same i/o before core power sequence and is also a DSP only device.

  • in reply to Bernie Thompson TI
    Genius 3575 points

    Are there any power down sequence requirements, specifically for the dm643x?  I couldn't find any in the datasheet and don't know if I have to reverse the power on sequence.

  • in reply to MattLipsey
    TI__Mastermind 41665 points

    Typically there is no true power down sequence, as when you are cutting power to the part you do not really care about if the device is in a logically valid state by the time you are done since it will be off which by is essentially a null state anyway. I would suggest that you do not leave one rail powered while another rail is off for too long through to make sure the part is not damaged by having an odd voltage condition like that, but usually when you are pulling the plug both rails will be gone almost immediately anyway so this is not typically an issue.