How can I calculate the maximum operating frequency of a level shifter (voltage translation logic IC)?

Each calculation method is briefly described below.

• The maximum operating frequency of the bus buffer type can be calculated from the propagation delay times (tpLH, tpHL) as shown below.
  Maximum operating frequency ≈ 1/(t_pLH ＋ t_pHL)
• The maximum operating frequency of the bus switch type can be calculated based on the CR time constant of the load and on-resistance.
  Maximum operating frequency ≈ 1/(τ), where τ is a time constant:
  Since τ is determined by charging and discharging time, τ is calculated from the time required for the output voltage to reaches 63 %. (See the Fig. 1.)
  1/τ = 1/(C×R)

For example, the TC7SPB9306 with a switch I/O capacitance (C_I/O) of 14 pF. Assume a load capacitance (C_L) of 30 pF and a pullup resistor (R_pu) of 1 kΩ. Then, τ is calculated as follows:
τ = (14 pF + 30 pF) × 1 kΩ
Hence, the maximum operating frequency is calculated as roughly 20 MHz

• Refer to the following FAQ for recommended level shifters that are compatible with the communications standard.
  FAQ: Are there level shifters (voltage translation IC) compatible with serial communication standards (UART, I²C)?

The result of this calculation should be considered merely as an estimate under the conditions shown in the datasheet.
Level shifters should be sufficiently evaluated to ensure that they work properly under the actual operating conditions because their propagation delay times change with the board capacitance and other conditions.