Use this electronics calculation for a first-pass component, converter, signal, motor, or sensor estimate when the stated operating conditions and units match the device data.

Rise time (ns)

Required number input.

Bus capacitance (pF)

Required number input.

Compute the maximum I2C pull-up resistance from the bus rise time and total bus capacitance using Rp(max) = trise / (0.8473 x Cb). The tool evaluates the supplied inputs together and returns the named outputs below; it does not infer omitted operating conditions or change the units shown.^[1]

Maximum pull-up resistance (Ω)

The resulting maximum pull-up resistance returned as a number.

• I²C pull-up and capacitance estimates depend on supply voltage, logic thresholds, sink-current limits, rise-time mode, trace and device capacitance, level shifters, topology, and bus speed. Confirm the complete bus against the applicable I²C timing specification and every device datasheet.
• Use finite inputs in the displayed units and preserve more precision than the final presentation requires. Independently verify safety-critical, financial, compliance, or production decisions.

Check the result against the current datasheet and worst-case operating corners, then verify the circuit or measurement with simulation and bench testing where failure matters.

• I2C Pullup Min

  Compute the minimum I2C pull-up resistance from VDD, the maximum output low voltage, and the sink current.

• I²C Bus Capacitance

  Sum device input capacitance and wiring capacitance to estimate total I²C bus capacitance. Use datasheet values and include all connected devices; whether the result meets a limit depends on the I²C mode.

• Max Resistance

  Compute the maximum resistance as nominal ohms times (1 + tolerance percent / 100).