The pull-up resistors, R_P, for the SCL and SDA lines need to be selected appropriately and take into consideration the total capacitance of all responders on the I²C bus. The minimum pull-up resistance is a function of V_CC, V_OL,(max), and I_OL:

Equation 1.

The maximum pull-up resistance is a function of the maximum rise time, t_r (120 ns for fast-mode-plus operation, f_SCL = 1 MHz) and bus capacitance, C_b:

Equation 2.

The maximum bus capacitance for an I²C bus must not exceed 400 pF for standard-mode or fast-mode operation, or 550pF for fast-mode-plus. The bus capacitance can be approximated by adding the capacitance of the TCAL9539, C_i for SCL or C_io for SDA, the capacitance of wires/connections/traces, and the capacitance of additional responders on the bus.