The TISP61089 is a dual forward-conducting
buffered p-gate overvoltage protector. It is
designed to protect monolithic SLICs (Subscriber
Line Interface Circuits) against overvoltages on
the telephone line caused by lightning, a.c.power contact and induction. The TISP61089 limits voltages that exceed the SLIC supply rail voltage. The
TISP61089 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 supply
voltage the overvoltage stress on the SLIC is minimised.
Positive overvoltages are clipped to ground by diode forward conduction. Negative overvoltages are initially
clipped 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 holding
current 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 suitable
overcurrent protector. Power fault compliance requires the series overcurrent element to open-circuit or
become high impedance (see Applications Information). For equipment compliant to ITU-T recommendations
K20 or K21 only, the series resistor value is set by the power cross requirements. For K20 and K21, a
minimum series resistor value of 10 W is recommended.
These monolithic protection devices are fabricated in ion-implanted planar vertical power structures for high
reliability and in normal system operation they are virtually transparent. The TISP61089 buffered gate design
reduces the loading on the SLIC supply during overvoltages caused by power cross and induction. The
TISP61089 is available in 8-pin plastic small-outline surface mount package and 8-pin plastic dual-in-line
package.