Hi all,
I am in the process of designing a custom expansion board for the MinnowboardMax (really liking my experience with this board so far BTW :-) and have a question regarding PCIe power supplies. One of the interfaces I am implementing on the expansion board is a Mini PCIe card slot. On my expansion board, I have all the required power suppliers for card slot, and hence don't need to rely on any power coming from the MinnowboardMax expansion connector. There is a requirement in the Atom e38xx documentation (actually a PCI Express 2.0 spec requirement) that all power rails associated with PCIe should be valid for ~100ms prior to PMC_CORE_PWROK assertion. >From what I can see in the MinnowboardMax schematic, there is an RC which controls the assertion of SYS_PWRGD providing 100ms delay as part of the power sequencing. My understanding is that as long as I ensure that my PCIe supplies are up before providing 5V to the MinnowboardMax, then I should be meeting this requirement. So a couple of questions just for clarification: 1) Is this an acceptable approach to take given the MinnowboardMax power supply architecture? I have a seen there is a Lure expansion board that includes mini PCIe and I presume this derives the required supplies from those provided on the expansion header (perhaps the +5VSB supply, which should also mean this constraint is met). 2) Any other recommended design approach? Backfeeding is always one area of concern I have which I need to manage carefully - just want to make sure there is nothing else I am overlooking/am not aware of. 3) I am intending on using #PMC_PLTRST_R_V1P8 as the system reset signal for PCIe card slot and some other devices (with appropriate buffers) - any thoughts here? Many thanks for any information/clarification! Regards, Leigh
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