SCPS221G October 2010 – November 2018 TCA9406
The continuous dc-current "sinking" capability is determined by the external system-level open-drain (or push-pull) drivers that are interfaced to the TCA9406 I/O pins. Since the high bandwidth of these bidirectional I/O circuits is used to facilitate this fast change from an input to an output and an output to an input, they have a modest dc-current "sourcing" capability of hundreds of micro-Amps, as determined by the internal 10-kΩ pullup resistors.
The fall time (tfA, tfB) of a signal depends on the edge-rate and output impedance of the external device driving TCA9406 data I/Os, as well as the capacitive loading on the data lines.
Similarly, the tPHL and max data rates also depend on the output impedance of the external driver. The values for tfA, tfB, tPHL, and maximum data rates in the data sheet assume that the output impedance of the external driver is less than 50 Ω.