Pull-up Resistor Sizing

Sinking Limit

Excessively small pull-up resistors draw high current when open-drain transistors pull lines low. Incorrect pull-up resistor sizing can exceed the three-milliamp current limit of standard sensor outputs, raising output low voltage levels above logic zero thresholds. Operating within safe current limits prevents output driver damage.

Rise Constraint

Large resistance values prolong RC charge times on signal lines with high bus capacitance. Slower rise times cause timing violations on fast-mode buses. Choosing lower resistance values speeds up edge transitions at the expense of higher power dissipation during low states.

Calculation Verification

Oscilloscope measurements verify signal rise times from ten percent to seventy percent of supply voltage. Design validation confirms logic zero voltage levels remain comfortably below input low thresholds. Standard engineering calculations document compliance across worst-case tolerance variations.