The TISP61089 is a dual forward-conductingbuffered p-gate overvoltage protector. It isdesigned to protect monolithic SLICs (SubscriberLine Interface Circuits) against overvoltages onthe telephone line caused by lightning, a.c.power contact and induction. The TISP61089 limits voltages that exceed the SLIC supply rail voltage. TheTISP61089 parameters are specified to allow equipment compliance with Bellcore GR-1089-CORE, Issue 1.The SLIC line driver section is typically powered from 0 V (ground) and a negative voltage in the region of-10 V to -75 V. The protector gate is connected to this negative supply. This references the protection(clipping) voltage to the negative supply voltage. As the protection voltage will then track the negative supplyvoltage the overvoltage stress on the SLIC is minimised.Positive overvoltages are clipped to ground by diode forward conduction. Negative overvoltages are initiallyclipped close to the SLIC negative supply rail value. If sufficient current is available from the overvoltage, thenthe protector will crowbar into a low voltage on-state condition. As the overvoltage subsides the high holdingcurrent of the crowbar prevents d.c. latchup.The TISP61089 is intended to be used with a series combination of a 25 W or higher resistance and a suitableovercurrent protector. Power fault compliance requires the series overcurrent element to open-circuit orbecome high impedance (see Applications Information). For equipment compliant to ITU-T recommendationsK20 or K21 only, the series resistor value is set by the power cross requirements. For K20 and K21, aminimum series resistor value of 10 W is recommended.These monolithic protection devices are fabricated in ion-implanted planar vertical power structures for highreliability and in normal system operation they are virtually transparent. The TISP61089 buffered gate designreduces the loading on the SLIC supply during overvoltages caused by power cross and induction. TheTISP61089 is available in 8-pin plastic small-outline surface mount package and 8-pin plastic dual-in-linepackage.