TISP61089AS

The TISP61089AS is a dual forward-conducting buffered p-gate overvoltage protector. It is designed to protect ringing SLICs (Subscriber Line Interface Circuits)  against overvoltages on the telephone line caused by lightning, a.c. power contact and induction. The TISP61089AS limits voltages that exceed the SLIC supply rail voltage. The TISP61089AS 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 -100 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, then the 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 TISP61089AS is intended to be used with a series combination of a 25   or higher resistance and a suitable overcurrent protector. Power faultcompliance 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 system operation they are virtually transparent. The TISP61089AS buffered gate design reduces the loading on the SLIC supply during overvoltages caused by power cross and induction.

The TISP61089AS is the TISP61089AD 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 The feed-through Ring (leads 4 - 5) and Tip (leads 1 - 8) connections have been replaced by single Ring (lead 4) and Tip (lead 1) connections.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. This increased spacing eases the design task of compliance with various safety standards, such as UL 1950.