nRF52840 Powering SD-card from VDD in high voltage mode

[Ivan Herrera]

Hi! I'm planning out the connection of a micro-SD card through SPI to the nrf52840. I'm reading through the documentation and when powering the nrf using a Li-Po through VDDH (in high voltage mode), there is VDD voltage will be 1.8V by default because REGOUT0 is set to 0 by default. Does this mean that I have to set REGOUT0 to 3.3V to successfully power the SD-card through VDD? 

On top of that, if the Li-Po voltage (VDDH) drops below 3.3V, will VDD drop with it or will the nRF52840 regulate it to 3.3V? 

[Jørgen Holmefjord]

Hi,

The operating voltage depends on the SD card type. Standard SD cards has a operating voltage of 3.3 V and you need to configure the REGOUT0 voltage accordingly.

As described in the REGOUT0 documentation, "The maximum output voltage from this stage is given as VDDH - VEXDIF" I could not find VEXDIF specified in the PS, but it should correspond to the V_REG0,DROP in this table.

You should make sure the supply voltage does not drop below ~3.6V with REGOUT0 set to 3.3V, or you should set it to a lower voltage and add a 3.3V regulator/level converter to interface the SD card.

Best regards,
Jørgen

[Ivan Herrera]

Thanks! Very clear answer.