Mity CPU Platforms » MitySOM-AM62 & MitySOM-AM62A

Hi Paul,

The VSEL_SD pin is connected to pin 12 of a TPS65219 PMIC on the SOM. VSEL_SD selects which voltage is applied to the AM62x VDDSHV5 voltage domain. The voltage is also present on the edge connector pin 172 as (VDDSHV_SDIO). On the AM62x, the MMC1 CLK, CMD, and DATA pins are powered by VDDSHV5.

When the VSEL_SD pin is asserted high, this domain will be 3.3V. When the VSEL_SD pin is asserted low, this domain will be 1.8V.

Note: on revision 2 and all future production SOMs, the SOM will include a 4.7K pull up to +3.3V. On revision -1 SOMs, there is no pull up present on VSEL_SD. To use -1 SOMs (only a handful were shipped, all future deliveries will be -2 or higher), you must include one on the carrier card to ensure that the VDDSHV5 SDIO IO voltage is correctly set to +3.3V during power up. This is critical if the an SD Card on MMC1 is used as the primary boot media. This is documented with some additional detail in the product change notification (PCN) from February 2023. Module Errata and PCN data may be downloaded from this page. I would strongly suggest navigating to that page and clicking the "watch" star on the upper right. This will cause you to receive an email notification when any updates to the page occur (future errata / PCNs should they occur, etc.).

With regards,
Mike

Pal Szabo wrote:

What is the functionality of the VSEL_SD pin (position 176 on the SODIMM connector)? Is it the same signal as VD_SEL mentioned in Note 8 in the MitySOM-AM62 datasheet on page 18? The datasheet does not contain more information about it, whereas the development board schematics connects it to a GPIO.

This is a typo, Note 8 should read VSEL_SD in the datasheet. There is a similar typo in PCN20230205000

To be clear: For sdcard operation: VSEL_SD should be connected to a gpio pin on the SOM, ideally gpio0_31 (pin 174) to keep software compatibility with the devkit. A 4.7k pull-up can be added if you need to support early -1 rev SOMs.

The software side of the SD voltage selection is configured here:

https://support.criticallink.com/gitweb/?p=linux-ti.git;a=blob;f=arch/arm64/boot/dts/ti/k3-am62x-mitysom-devkit.dts;h=725aba2f30bb44c86b9d86d432cae15f3b08f067;hb=refs/heads/mitysom-linux-5.10.y#l122

https://support.criticallink.com/gitweb/?p=linux-ti.git;a=blob;f=arch/arm64/boot/dts/ti/k3-am62x-mitysom-devkit.dts;h=725aba2f30bb44c86b9d86d432cae15f3b08f067;hb=refs/heads/mitysom-linux-5.10.y#l658

Thank you very much to both of you for the quick and extensive answer. The key information that the voltage of VDDSHV5 is controlled via the VSEL_SD pin might be worth putting into the datasheet. Special thanks for the pointers on the errata and the PCN, I overlooked those documents.

Best regards,
Paul

No problem. I condensed all this info into a wiki page for future reference as well. And have initiated changes for our datasheet and errata to correct the signal name.

https://support.criticallink.com/redmine/projects/mitysom_am62x/wiki/Boot_sd#Hardware-design-considerations