IMX6ULL SD_VCC regulator does not go to 1.8V

Technical Support
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1

Hi,

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,
Arnout

2

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.

3

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

4

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.

5

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

Many thanks for the prompt response!

6

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