• State Resolved
  • Locked Locked
  • Replies 9 replies
  • Subscribers 99 subscribers
  • Views 156 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AM62A3-Q1: HW:SDCD Interface

Koji Kinoshita
Intellectual 330 points
Part Number: AM62A3-Q1


Hello experts.

When using SDCD, is it possible to configure the power supply and signal level on the SDCD side to be only 1.8V?

Thanks and beset  regards.

Kinoshita.

  • +1
    TI__Guru 63445 points

    I'm not sure which MMC port you are asking about.

    The SDCD signal function associated with the MMC1 port is part of the VDDSHV0 IO power domain, so this signal must operate from the same power supply that is sourcing VDDSHV0.

    The SDCD signal function associated with the MMC2 port has three pin multiplexing options, where two are part of the VDDSHV0 power domain and the other is part of the VDDSHV6 power domain. The operating voltage of this signal must be from the same source being used to power the respective IO (VDDSHV0 or VDDSHV6 power domain).

    I do not understand why this is a concern. Normally the SDCD signal is only connected to switch on the SD Card slot, where the signal is pulled high with a pull-up connected to the same power rail that is powering the associated IO and the switch in the SD Card slot will pull the signal to VSS when a card is inserted. The switch doesn't care what voltage is applied to the pull-up.

    Regards,
    Paul

  • 0 in reply to peaves
    Intellectual 330 points

    I understand about SDCD.
    When the VDDSHV5 is set to 1.8V using MMC1, the signals of DATA, CLK, and CMD are 1.8V, but is it possible to write to and read from the SD Card?

    BR,
    Kinoshita.

  • 0 in reply to Koji Kinoshita
    TI__Guru 63445 points

    SD cards begin operation at 3.3V. If using a UHS-I SD card, the software driver will request an IO voltage change to 1.8V for the higher speed modes. If you plan to support the higher speed modes of these cards, you will need to implement a dual voltage VDDSHV5 power supply that is able to change voltage at the same time the card is told to change voltage. Otherwise, you can power VDDSHV5 from a fixed 3.3V source if do not need to support the faster modes that require the signals to dynamically change from 3.3V to 1.8V. You should look at the TI EVM for an example of how to implement the SD card and VDDSHV5 power sources.

  • 0 in reply to peaves
    Intellectual 330 points

    I don't plan to use the UHS-I SD Card, so I'll consider using it with a 3.3V power supply.

  • +1 in reply to Koji Kinoshita
    TI__Guru 63445 points

    We still recommend implement a 3.3V load switch that sources the SD card and the MMC1 VDDSHV5 IO power rail with its enable controlled by a three input AND of the power on reset, AM62Ax warm reset output, and a GPIO that is pulled high until configured by software. This is needed to reset the SD card since it doesn't have a reset pin. The only way to reset an Sd card is cycle its power and the AM62Ax VDDSHV5 IO rail must be cycled at the same time to avoid non-fail-safe conditions. This implementation will reset the card anytime the system power is cycled, a warm reset is generated like in the case where a watchdog time resets the processor, or if the SD card software driver needs to reset it via a GPIO without resetting the entire system.

    Regards,
    Paul

  • 0 in reply to peaves
    Intellectual 330 points

    Hello Paul

    The VDDSHV5 is always supplied, and the power supply of the SD card is loaded with a load switch.
    Is there a problem if the VDDSHV5 is always supplied to the SD card after SDCD is detected?
    Is it a substitute for a RESET if I put a load switch on the power supply to the SD card?

    Do I really need three inputs, SD_EN, RESETSTATz, and PORz_OUT, to power enable the SD card?
    Is it possible to achieve this with two signals, SD_EN and RESETSTATz?

    Regards,
    Kinoshita

  • +1 in reply to Koji Kinoshita
    TI__Guru 63445 points

    The IOs associated with both the AM62Ax device, and the SD Card are not fail-safe. This means no external circuit can source any potential greater than the potential applied to the respective IO power rail. See the "Steady-state max voltage at all other IO pins" parameter in the Absolute Maximum Ratings table in the datasheet, where the potential applied to a pin is limited to minimum of "-0.3V" and a maximum of "IO supply voltage + 0.3V".  The same limit should be applied to the SD Card pins.

    The IO power rails of attached devices need to always have the same potential applied to prevent current injection into an IO that has a potential applied greater than the limits defined in the datasheet. For example, if one device is turned on the other device must be turned on, if one device is turned off the other device must be turned off. Their IO supplies also need to track as the power source ramps up or down. The best way to ensure this condition, is to power the IOs associated with both devices from the same power source.

    For the SD Card use case, the VDDSHV5 power rail on AM62Ax, the SD Card, and any external pull-up resistors need to be powered by the load switch.

    For AM62Ax the MMC1 IOs default to an off state, so we recommend external pulls on the MMC1 signals to hold the inputs of the attached SD Card in valid logic state until the device has booted, and software configures the IOs. An external pull-down resistor is recommended for the CLK signal and external pull-up resistors are recommended for each of the CMD and DAT[3:0] signals. The external pull-up resistors should be powered from the same switched 3.3V power that is connected to the SD Card and the VDDSHV5 power rail.

    Our reset expert said the PORz_OUT would not be needed since the RESETSTATz output will satisfy all reset cases for the SD Card.

    Regards,
    Paul

  • +1 in reply to peaves
    TI__Guru 63445 points

    I need to clarify my last reply. I should have said the RESETSTATz output will satisfy the power-on and warm reset functions for the SD Card. You will still need a two input AND gate to insert the software controlled GPIO reset function for the case where software needs to initiate a reset to only the SD Card.

    The software GPIO reset function originates form an IO expander on the TI hardware platform, but you could use a GPIO signal function associated with one of the AM62Ax pins if your system doesn't include the IO expander. Select an AM62Ax pin with a GPIO multiplexing option that is turned off by default. Connect a signal from this pin to the other input of the AND gate and include a pull-up on this signal so the SD Card is brought out of reset as soon as the RESETSTATz goes high. Software can configure the AM62X pin to operate as GPIO after boot and drive it low if it needs to reset the SD Card.

    Regards,
    Paul

  • +1 in reply to peaves
    TI__Mastermind 18105 points

    Kinoshita-san

    I would like to know if your question has been solved.

    If not yet, I would like to ask you to put your feedback here.

    Best Regards

    KORO