OCTOBER 2000 - REVISED FEBRUARY 2005

Specifications are subject to change without notice.

Customers should verify actual device performance in their specific applications.

APPLICATIONS INFORMATION

Figure 10 shows a typical TISPPBL3 SLIC card protection circuit. The incoming line conductors, R and T, connect to the relay matrix via the

series overcurrent protection (RSA and RSB). Fusible resistors, fuses and positive temperature coefficient (PTC) thermistors can be used for

overcurrent protection. Normally, the SLIC reference designs recommend using 40 Ω matched fusible resistors, such as the Bourns 2x40 Ω,

2 % tolerance, 0.5 % matched 4B04B-523-400 or the 4B04B-524-400 with a thermal fuse. These resistors will reduce the prospective current

from the surge generator for both the TISPPBL3 and the ring/test protector. The TISP7xxxF3 protector has the same protection voltage for any

terminal pair. This protector is used when the ring generator configuration may be ground or battery-backed. For dedicated ground-backed

ringing generators, the TISP3xxxF3 gives better protection as its inter-conductor protection voltage is twice the conductor to ground value.

Relay contacts 3a and 3b connect the line conductors to the SLIC via the TISPPBL3 protector. Closing contacts 3a and 3b connects the

TISPPBL3 protector in parallel with the ring/test protector. As the ring/test protector requires much higher voltages than the TISPPBL3 to

operate, it will only operate when the contacts 3a and 3b are open. Both protectors will divert the same levels of peak surge current, and their

required current ratings should be similar. The TISPPBL3 protector gate reference voltage comes from the SLIC negative supply feed (VB). A

local gate capacitor, C1, sources the gate current pulses caused by fast rising impulses.

TISPPBL3 Voltage Limiting Performance (continued)

TISPPBL3 Programmable Protector

Figure 9. SLIC Voltage Ratings And TISPPBL3 Protection Levels

Time

SLIC MINIMUM VOLTAGE WITHSTAND

AND TISPPBL3 VOLTA GE LIMITING

vs

TIME

0

10

20

30

40

AI6XDF

TISPPBL3

TISPPBL3

V

V

V

V

V

BAT

1 µs

0.25 µs

10 ms

0.7 V ISOLATION DIODE (D1)

VOLTAGE DROP FROM V

Bat

Application Circuit