NRF24L01+ Compatibility with 1.8v uC

[mattgaidica]

I would like to use the NRF24L01+ from a 3v coin cell, but interface it over SPI with a 1.8v-powered microcontroller. Assuming the uC is tolerant of the NRF SPI outputs, I am wondering if the SPI inputs to the NRF will reliably work if they are 1.8v? Board space is limited, so performing a level conversion is not ideal. Thanks,

[mattgaidica]

It appears this would be problematic since "Table 12. Digital input pin" states that "high level" = 0.7*VDD, in this case, 0.7*3v=2.1v, which is less than 1.8v. Therefore, 1.8v logic would not be reliable on the SPI pins. My proposed solution is to instead use a 1.9v regulator for my uC, which will also meet the power supply demands of the nRF24L01+ and make the SPI bus operate at 1.9v. 

[Håkon Alseth]

Hi,

 

mattgaidica said:

My proposed solution is to instead use a 1.9v regulator for my uC, which will also meet the power supply demands of the nRF24L01+ and make the SPI bus operate at 1.9v. 

This would be a less intrusive workaround (space-wise), compared to a lvl shifter.

I would recommend that you keep the VDD_NRF a bit higher than the minimal voltage (1.9 + 0.1 V, for instance), to account for any dips or ripple in the supply. 

 

Kind regards,

Håkon