JAJSHO4D January 2014 – November 2019 TCA9545A
Once all the slaves are assigned to the appropriate slave channels and bus voltages are identified, the pull-up resistors, Rp, for each of the buses need to be selected appropriately. The minimum pull-up resistance is a function of VDPUX, VOL,(max), and IOL:
The maximum pull-up resistance is a function of the maximum rise time, tr (300 ns for fast-mode operation, fSCL = 400 kHz) and bus capacitance, Cb:
The maximum bus capacitance for an I2C bus must not exceed 400 pF for fast-mode operation. The bus capacitance can be approximated by adding the capacitance of the TCA9545A, Cio(OFF), the capacitance of wires/connections/traces, and the capacitance of each individual slave on a given channel. If multiple channels will be activated simultaneously, each of the slaves on all channels will contribute to total bus capacitance.