8.4.3 ICUT Current Limit

In addition to the absolute current limit imposed by the ILIM foldback curve (Figure 58) the TPS23861 supports an additional level of current-limit protection.

When the ICUT current-limit threshold is reached, the TICUT timer starts counting down. When it reaches zero the port is powered down. If the port current drops below the ICUT current-limit threshold while the TICUT timer is counting, the TICUT timer counts up, albeit at a slower rate, without exceeding the maximum count corresponding to the setting in the TICUT field.

The ICUT current-limit threshold is meant to be applied such that its setting is below the setting of the ILIM current limit. That is, the ICUT threshold should be reached before the TPS23861 asserts foldback control over the port current via an ILIM current limit. To this end, the ICUT threshold should be set lower than the ILIM current limit. This must be accomplished by the host except when in Auto Mode (or the AUTO bit is set). In that case, the settings for ICUT and ILIM is properly set based on classification results before the port is powered on.

The ICUT current limit threshold (ICUT) is programmable on a per-port basis in the 3-bit ICUT Port n fields in the ICUTnm CONFIG registers. The encoding of the ICUT Port n fields is shown in Table 15. The current values in Table 15 are nominal values.