This DS9502 is an ESD protection device for 1-Wire® interfaces. If used with circuits that already have strong ESD production at their I/O port, the ESD protection level is raised to more than 27kV (IEC 801-2 reference model). In case of abnormal ESD hits beyond its maximum ratings the DS9502 will eventually fail "short" thus preventing further damage.
During normal operation the DS9502 behaves like a regular 7.5V Zener diode. When the voltage exceeds the trigger voltage, the I/V characteristic of the device will "snapback" allowing the same or higher amount of current to flow, but at a significantly lower voltage. As long as a minimum current or voltage is maintained, the device will stay in the "snapback mode." If the voltage or the current falls below the holding voltage or holding current, the device will abruptly change to its normal mode and conduct only a small leakage current.