According to the documentation, when VIO_SEL pin is grounded, the maximum UART voltage level is 3.3V and follows VBAT if lower. Our measurements show there is some voltage drop between VBAT and MAIN_TXD and it does not go above approx. 3.2V.
- Is LDO or something similar used internally to power the UART?
- Are there any protection diodes used? What type?
- Our MCU normally runs on 3.6V (sometimes going up to 3.7V). Receiving from 3.2V level is completely fine (3.2V is bigger than 0.7*VBAT), but I’d like to check if we can send VBAT directly to MAIN_RXD. We can add series resistor if needed. When tested there is no additional current flow measured so I assume it should work fine (despite the documentation).
- Is there any difference in power consumption depending on VIO_SEL mode?