SCPS267B March 2017 – February 2020 TCA9803
The SCLA and SDAA pins enters a high impedance state when either VCCA or VCCB fall below their UVLO voltages. These pins are safe to continue having I2C communication on, even when the device is disabled or has no power.
The SCLB and SDAB pins remain powered by their current source (ICS), even when VCCA is below UVLO. When VCCB falls below UVLO, the current source turns off, and a weak pull-up is connected to prevent the B-pins from floating. This is intended behavior, because no external pull-up resistors are to be used on the SDAB or SCLB pins. This behavior prevents the bus pins from floating, and allows it to follow VCCB.