IMX6ULL SD_VCC regulator does not go to 1.8V


For the design of a new colibri carrier boards, we were looking into the possibility of using SDHC1 on a fixed 1.8V level for interfacing with an SDIO module.

The toradex colibri datasheet clearly specifies that SD1_CLK, SD1_CMD and the first 4 datalines can be powered at 1.8V.

From what I see in the linux kernel device tree, the reg_sd1_vmmc regulator is used for this, which is controlled by GPIO5_9 (MX6ULL_PAD_SNVS_TAMPER9__GPIO5_IO09).
As far I can see, driving this pin high should cause some regulator on the IMX SOM to drop the NVCC_SD to 1.8V, and hence lower the bank voltage.

To confirm this, I quickly did a test, where I disable the regulator control in the device tree and put both MX6ULL_PAD_SNVS_TAMPER9 and MX6UL_PAD_SD1_CLK in GPIO mode, and drive the signals.

The result is however that with MX6ULL_PAD_SNVS_TAMPER9 driven high, the output of SD1_CLK goes down to 3V, but NOT to 1.8V.

Am I missing something here?
What is the internal connection of NVCC_SD on the module? Is my understanding correct of trying to manually force the 1.8V? If not, how can this be achieved then?

Thanks for your reply,

Dear @Arnout,

thanks a lot for using the Toradex community.
First of all, I would like to ask which carrier board are you using for this test?
Do you remove the pull-up resistors on the CMD and Data lines?
Thanks for your feedback.

Hi Diego,

I am using the colibri Evalboard V3.2B. I disconnected the jumper between X10 and X12 for SODIMM_47 (SD1_CLK),

Thanks for your reply

Hi @Arnout,

could you please also disconnect the other signals, to make sure the data lines and CMD are not pulled up? This is just a quick test you can do and, if it does not change, I will have somebody from the SW team providing you the required information.

Ha! Indeed, that fixes it! The voltage of the bank was being powered by the other pins!

Many thanks for the prompt response!

Hi @Arnout,
that was actually my idea, I am glad that it helped. Please don’t hesitate to use again the community if needed.