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[FAQ] AM6442: AM6442 SD card interface

Balaji Appadurai45
Prodigy 200 points
Part Number: AM6442

hi,

I was referring to Starter kit Schematic and EVM schematic of AM6442, I would like to know the reason for having Switched power rail which is enabled based on reset status for SD card interface. I had done the same Circuit using AM4378x in the past where I did not used the switching power rail. Does AM6442 demand for switched Power supply based on the processor Reset?

What is the down side if I directly connect the 3.3V to SD Card ?

Here is the schematic screenshot for your quick reference, I’m unable to find the relevant topic in e2e forum. Can you please clarify it?

 

  • +1
    TI__Guru 59845 points

    This power switch, along with the reset logic, and the host IO power supply circuit is required to support UHS-I SD Cards which begins communications using 3.3V signal levels and later change to 1.8V signal levels when changing to one of the faster data transfer speeds. Cycling power to the SD Card is the only way to put it back into 3.3V mode since SD Cards do not have a reset pin. The host IO power supply must power off/on and change voltage at the same time as the SD Card. These circuits and the software driver operating the signals sourcing these circuits ensure both devices are off, or on and operating at the same IO voltage at the same time. 

    Regards,
    Paul

  • 0 in reply to peaves
    TI__Guru 59845 points

    I made an edit to my previous post.

  • 0 in reply to peaves
    Prodigy 200 points

    thank you for the quick response.