Is VDD (VDD_INTRNL) off limits?

[coloradocarlos]

Our company will be using an eMMC for onboard storage just like on the RED board.

Rather than supplying power solely from VDD_3V3 (buck 4), we are considering a design to supply eMMC VCC with VDD_3V3 and VCCQ with VDD (buck3). Likewise, pull up nRST to VDD. This split has to do with preventing nRST from going low when VDD_3V3 is turned off and causing a system reset which defeats STM32 Standby mode for poweroff (i.e. shutdown -h 0).  See the standby-ddr-off node in the TF-A device tree.

The schematic for the RED board shows VDD for “Internal Use Only”. Is VDD “off limits” and can’t or shouldn’t power logic elsewhere?

[Neeraj Dantu]

Carlos,

Since VDD is being used internally and there is a variable load on this rail, we do not recommend using it to power external devices. As note 3 under Table 8-2 in the datasheet(https://octavosystems.com/docs/osd32mp15x-datasheet/) suggests, you can use it for pull up resistors. There are other power rails you can use to power the eMMC listed in table 8-2 of the datasheet. This will allow you to control the power to the eMMC for low power states.

Best,

Neeraj

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