I'm currently using the I2C switch PCA9545 and PCA9548 in my design, and I have several questions about the output pin.
1) Are the SDn/SCn output pins open-drained? Judging from the necessity of pull-up resistors, we assume they are open-drained, but no evidence can be found in the datasheet.
2) In the datasheet, the voltage translation is explained by an instance, in which the upstream bus has the highest voltage (5V) among all of the downstream buses (3.3V and 2.7V), and the design guide demands that the PCA954X should be powered with the lowest I2C bus voltage(2.7V) . My question is whether it is okay when upstream voltage is lower than (and furtherly, the lowest in) all of the downstream buses? For instance, if the SDA/SCL input is 1.8V, and all SDn/SCn is 3.3V, should we power the PCA954X switch with VDD=1.8V?