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[FAQ] AM625: SD card (MMC1) VDD power supply

Part Number: AM625
Other Parts Discussed in Thread: SK-AM62-LP

Tool/software:

Hi,

My customer is using SD card boot only for development phase. For production, only QSPI boot is used.
QSPI or SD card boot selection is done by DIP switch on the board.
SD card insertion or removal is done when the board is power off.

Question:
Below schematics is SK-AM62-LP board MMC1 power supply block.

VDD_MMC1_SD is on / off by the reset logic.
The customer is planning to remove the reset logic and VDD_MMC1_SD is directly connected to VCC_3V3_SYS.
Is this a problem?
According to the D-Note, power cycle is needed to reset the SD card (back to 3.3V mode).
I guess;
If only SoC is reset, MMC1 IO voltage is back to 3.3V as default, but SD card is still 1.8V mode and it causes voltage mismatch, correct?

Thanks and regards,
Koichiro Tashiro

  • The 3.3V power switch controlled by the three input AND gate is needed to cycle power to the SD Card and the AM62x MMC1 IO power supply. The SD Card does not have a reset input, so cycling power is the only way to reset it. You must also cycle power to the AM62x MMC1 pins anytime you cycle power to the SD Card because the SD Card inputs are not fail-safe. Having the reset capability is very important for UHS-I SD Cards because this is the only way to force the SD Card back to 3.3V mode after it was changed to operate in 1.8V mode.

    I would not recommend a direct connection to 3.3V if you plan to support UHS-I SD Cards.

    Regards,
    Paul