Power down NVCC_SD0

[andrewkinmont]

In the datasheet for the RT1064 processor, I note the following under the GPIO supplies in the Operating ranges table:

"All digital I/O supplies (NVCC_xxxx) must be powered (unless otherwise specified in this data sheet) under normal conditions whether the associated I/O pins are in use or not."

Further review of the datasheet does not appear to show any conditions where one of the NVCC_xxxx power rails could be powered down.

Is it possible to power down the NVCC_SD0 rail but keep all of the other NVCC_xxxx rails powered up?

We are looking at power switching for an SD card on this interface, and would like to be able to power down the SD card when it is not required. The reference design seems to power down the SD card socket, but leave power applied to the interface pins (NVCC_SD0 power pin, plus the pull up resistors on the CMD and D0 pins), but is there any reason why the NVCC_SD0 pin (and associated pull-ups) could not be powered down at the same time?

When we started out development using the preliminary datasheets, I did ask this question and was told that it was OK to power down the NVCC_SD0 rail with the other rails still powered up, however, I am concerned that the released datasheet does not appear to support this mode of operation. I would be grateful for getting this clarified.

Thanks,

Andrew

[Yuri]

Hello,

  The solution, provided on the EVK - to power down the SD card socket, but leave power,

applied to the i.MX pins (NVCC_SD0) is quite reasonable. It is correct for devices of the

i.MX series:- "All digital I/O supplies (NVCC_xxxx) must be powered ... under normal conditions

whether the associated I/O pins are in use or not."

   Also: -"All I/O pins should not be externally driven while the I/O power supply for the pin (NVCC_xxx)

is OFF. This can cause internal latch-up and malfunctions due to reverse current flows."

 
Have a great day,
Yuri

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[andrewkinmont]

Hi Yuri,

Thanks for getting back to me so quickly.

Does this cause any issues with leakage into the interface pins of the SD card when it is not powered? With the NVCC_SD0 permanently powered up, and with the pull-up resistors on a couple of the interface pins, I would expect leakage into the SD card.

Perhaps the SD card specification allows for this scenario, but I am not a member of SD Association, so I don't have access to the full Physical Layer specification.

Thanks,

Andrew

[Yuri]

Hello,

   SD card are protected.

Regards,

Yuri.

[andrewkinmont]

Thanks, Yuri.

While I am sure this is true, it will still result in a slightly higher power draw, since there will be leakage current through the card.

It also doesn’t sit well with me to implement a design that does not meet the specifications.

Regards,

Andrew