NVT4858 SD Card VCCB Power Configuration for UHS-I with STM32H723

[YYT]

I am using the NVT4858 SD card transceiver with an STM32H723 MCU to support SD UHS-I communication.

The NVT4858 MCU side (VCCA) is powered at 1.8V.
My question is about the SD card side (VCCB):
Should the SD card always be powered at 3.3V, or is it required to switch the SD card supply to 1.8V after the initialization phase, as specified in the UHS-I standard?

[JozefKozon]

Dear YYT,

The SD card is not required to be switched to 1.8 V.
With NVT4858, you may keep VCCB (SD card side) at 3.3 V permanently.
Switching the SD card supply to 1.8 V is optional and only required if you want to use UHS‑I high‑speed modes.

With Best Regards,

Jozef

[YYT]

Thank you for your reply. What I need is the communication rate of UHS-I DDR50. During initialization, both sides are at 3.3V, and after initialization, it switches to 1.8V. I would like to know if the power supply of VccB also requires me to design a circuit to switch accordingly?

[JozefKozon]

Dear YYT,

the VCCB side can stay at 3.3V. There is not need to switch the VCCB side to 1.8V. 

The NVT4858 supports VCCA voltage from 1.08V to 1.98V and VCCB voltage from 1.62V to 3.6V independently. It is capable to translate voltage from 1.8V to 3.3V and vise versa. You can choose any voltage from the VCCA and VCCB within boundaries.

With Best Regards,

Jozef

[YYT]

Thank you for your reply. I have a few more questions. When initializing my STM32H723ZGT6, the voltage is 3.3V, but the voltage on the VCCA side is 1.8V. Can I directly connect and use it? I am using UHS-1. Is the voltage on the VCCB side 3.3V during initialization, and switches to 1.8V after initialization is complete?

[JozefKozon]

Dear YYT,

Thank you for your reply. I have a few more questions. When initializing my STM32H723ZGT6, the voltage is 3.3V, but the voltage on the VCCA side is 1.8V. Can I directly connect and use it? I am using UHS-1. Is the voltage on the VCCB side 3.3V during initialization, and switches to 1.8V after initialization is complete?

[A] No. This will destroy the NVT4858. Please refer to the Table 8. in the NVT4858 datasheet. You must make sure, that any of the values listed there are not exceeded. If the VCCA=1.8V and you will apply 3.3V to the I/O pins on the VCCA side, this will exceed the maximum limit (VCCA+0.3V=1.8V+0.3V=2.1V) and destroy the NVT4858. 

With Best Regards,

Jozef