EN_HIZ has the function of stopping the converter, stopping the supply from Vbus, and discharging from the battery.

The following is an excerpt from the datasheet P15 9.3.1.3.6 HIZ State wth 100mA USB Host.

In HIZ state, the device is in the lowest quiescent state with REGN LDO and the bias circuits off.
REG00[7] to 1, and the VBUS current during HIZ state will be less than 30 µA.

See datasheet for details.
http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=BQ24192I&&fileType=pdf