TISP61089S

The TISP61089S 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 TISP61089S limits voltages that exceed the SLIC supply rail voltage. The TISP61089S parameters are specified to allow equipment compliance with Bellcore GR-1089- CORE, Issue 1.

The SLIC line driver section TISP61089S 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 TISP61089S is intended to be used with a series combination of a 25 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 is recommended.

These monolithic protection devices are fabricated in ion-implanted planar vertical power structures for high reliability and in normal systemoperationthey are virtually transparent. The TISP61089S buffered gate design reduces the loading on the SLIC supply during overvoltages caused by power cross and induction. The TISP61089S is the TISP61089D with a different pinout. The feed-through Ring (leads 4 - 5) and Tip (leads 1 - 8) connections have been replaced by single Ring (lead 4) and Tip (lead 1) connections. This increases package creepage distance of the biased to ground connections from about 0.7 mm to over 3 mm.