Hi Jacky,
Pin VIO is connected to the microcontroller supply voltage to provide the proper voltage reference for the input threshold of digital input pins and for the HIGH voltage of digital outputs. It defines the ratiometric digital input threshold for interface pins TXD, STB and S and the HIGH-level output voltage for RXD. Both the TJA1057/3 and TJA1044/3 provide a continuous level adaptation from as low as 2.95V to 5.25V.
In general, for a full flexibility between 5V and 3.3V applications it is recommended to use the variants with VIO pin.
Best regards,
Tomas
