SCPS267B March 2017 – February 2020 TCA9803
The IILC parameter is the minimum amount of current that the external device must sink from the TCA980x in order for the TCA980x to accept the low on the B-side.
In order for the TCA980x to accept a low on the B-side, both VIL and IILC parameters must be satisfied. In an idle bus condition (both A and B sides are high), meeting the VIL threshold with an external device pull-down meets the IILC requirement, since the pull-down has to sink the entire ICS (current source value) current before the voltage on the pin falls.
In a contention situation (the A-side is being driven low externally, and the B-side is driven low by the TCA980x), the VIL requirement is already satisfied by the TCA980x alone (Since the output low voltage is less than the VIL threshold). In order for a device on the B-side to over-drive the A-side, it must sink the IILC value for the TCA980x to accept that the low is now being driven by the B-side. This helps reduce or eliminate overshoot during the hand off between a slave an master during a clock-stretching event, or an acknowledge.
External pull-up resistors on the B-side are not allowed for this reason. As the additional current provided by them may hinder an external device from being able to satisfy the TCA980x's IILC requirement. For more information on this and allowed external current into the device, see the Input and Output Leakage Current (IEXT-I/IEXT-O) section.