ST25R3911B VDD Range

[KevinB]

This seems like an "easy" topic, yet I'm struggling to get a clear understanding.

Section 3.2 of the datasheet (Operating Conditions) defines a single, wide range for VDD (2.4V to 5.5V).  But Section 1.3.2 (IO Configuration Register 2) defines two non-contiguous VDD range (either 2.4V to 3.6V or 4.1V to 5.5V).  Does this indicate that VDD between 3.6V and 4.1V is not supported?

Based on Section 3.2, we did a HW design where VDD is powered from a battery (3.3V to 4.2V) and we have an issue where sometimes the Adjust Regulator command fails to complete (no interrupt received within 10ms).  And wondering if we are violating the supported VDD range.

I've also dug through RFAL001 and it looks like it sets sup3_V to 5V if VDD > 3.6V.  This also indicates the VDD range from 3.6V to 4.1V is not supported because (in 5V mode) the minimum VSP_RF is 3.9V and VDD has to be about 0.25V higher.

[KevinB]

As a follow-on question, since our battery powered VDD will almost always be below 4.1V, can we always force sup3_V to 3.3V mode?

[Ulysses HERNIOSUS · Accepted solution]

Hello KevinB,

ST25R3911B is designed for operation from either a fixed 5V or 3V3 supply - not so much for battery designs. You could use ST25R200 instead which should be clean of such limitations. 

If you need to stay on ST25R3911B then it could be an option to bypass the regulator - but not sure how clean your battery supply really is...

BR, Ulysses

[AScha.3]

If you want to stay on ST25R3911B , just put an 3v3 LDO to supply it.

So it has its stable 3v3 and is working fine. (Anyway you need/have an 3v3 LDO to supply the cpu - right? )

[KevinB]

Thanks Ulysses!  So apparently the full VDD range (2.4V to 5.5V) applies only if the VSP_RF regulator is bypassed!  I certainly don't see that stated anywhere in the datasheet, but it makes sense with all the other provided details.