The reference manual states that one must enable power following the rise of CARRIER_POWER_ON.
This is fully understood.
However, is there ANY special order in which the carrier board power supplies must rise?
Your carrier board schematic seems to start in this order +5V → +3V3 → +1V8, I assume this is because RESET_OUT is being held low from +1V8_PGOOD meaning it will only boot when all supplies are “on”.
May I reverse the order so that they start +1.8V → +3.3V → +5V and RESET_OUT is tied to +5V_PGOOD instead?
The reason I ask is that I have other chips on my board which requires this sequencing method.
Below is the comments from our HW team as your reference:
I believe that the sequence for the supplies on the carrier board is not critical. We use the 1.8V supply powergood to hold reset low and keep Tegra from booting because the 1.8V supply is the last one required for boot. If they need to have their supplies come up in a different order, they should be able to use the powergood from the last one as they mention (5V) to hold RESET_OUT# low. The only real concerns either way is that they don’t have pins on the carrier board that connect to Jetson pins driving/pulled high before the module asserts CARRIER_POWER_ON and that they don’t have any devices connected to pins shared with the module that could be negatively affected if they are driven/pulled high before their power rails is enabled. There is a section in the OEM DG that describes which module pins are pulled/driven high by Tegra or the module before CARRIER_POWER_ON is raised (section 12.3 Pins Pulled/Driven High During Power-on in the version I am looking at).