TISP40xxL1AJ/BJ VLV Overvoltage Protectors
TISP
®
Device Voltage Selection (Continued)
So a higher voltage protector might be chosen specifically to reduce the protector capacitive effects on the signal.
Low energy short duration spikes will be clipped by the protector. This will extend the spike duration and the data loss time. A higher protector
voltage will reduce the data loss time. Generally, this will not be a significant factor for inter-conductor protection.
However, clipping is significant for protection to ground, where there is continuous low-level a.c. common mode induction. In some cases the
induced a.c. voltage can be over 10 V. Repetitive clipping at the induced a.c. peaks by the protector would cause severe data corruption. The
expected a.c. voltage induced should be added to the maximum signal level for setting the protector V
DRM
value.
2-Wire Digital Systems
Typical systems using a single twisted pair connection are: Integrated Services Digital Network (ISDN) and Pair Gain.
Signal level protection at the transformer winding is given by protectors Th3 and Th5. Typically these could be TISP4015L1 type devices with a
15 V voltage protection level.
LINE
SIGNAL
T1
Th1
Th3
C1
Th2
OVER-
CURRENT
PROTECTION
OVER-
CURRENT
PROTECTION
Th4
C2
Th5
T2
SIGNAL
TRANSFORMER COUPLED TWO-WIRE INTERFACE
DC FEED
DC SUPPLY
AI4XAL
Figure 11. 2-Wire System
Two line protection circuits are given; one referenced to ground using Th1 and Th2 (left) and the other inter-wire using protector Th4 (right) - see
Figure 11. For ISDN circuits compliant to ETSI ETR 080:1993, ranges 1 and 2 can be protected by the following device types: TISP4095M3,
TISP4095H3, TISP3095H3 (combines Th1 and Th2) and TISP7095H3 (combines Th1, Th2 and Th4). Ranges 4 through 5 can be protected by:
TISP4145M3, TISP4145H3, TISP3145H3 (combines Th1 and Th2) and TISP7145H3 (combines Th1, Th2 and Th4). Device surge requirement, H
or M, will be set by the overcurrent protection components and the standards complied with. Protection of just the d.c. feed to ETSI ranges is
covered in the TISP5xxxH3 data sheet.
When loop test voltages exceed the normal d.c. feed levels, higher voltage protectors need to be selected. For two terminal protectors, for
levels up to 190 V (135 V rms) the TISP4250, H3 or M3, can be used and for 210 V (150 V rms) the TISP4290, H3 or M3, can be used.
In Pair Gain systems, the protector V
DRM
is normally set by the d.c. feed value. The following series of devices have a 160 V working voltage at
25
°C:
TISP4220M3, TISP4220H3, TISP3210H3 (combines Th1 and Th2) and TISP7210H3 (combines Th1, Th2 and Th4). These devices can be
used on 150 V d.c. feed voltages down to an ambient temperature of -25
°C.
Where the subscriber equipment may be exposed to POTS (Plain
Old Telephone Service) voltage levels, protector Th4 needs a higher working voltage of about 275 V. Suitable device types are: TISP4350M3,
TISP4350H3, TISP3350H3 (combines Th1 and Th2) and TISP7350H3 (combines Th1, Th2 and Th4).
The overcurrent protection for the overvoltage protector can be fuse, PTC or thick film resistor based. Its a.c. limiting capability should be less
than the ratings of the intended overvoltage protector. Equipment complying with the year 2000 international K.20, K.21 and K.45
recommendations from the ITU-T, may be required to demonstrate protection coordination with the intended primary protector. Without adding
series resistance, a simple series fuse overcurrent protection is likely to fail the equipment for this part of the recommendation.
If the d.c. feed consists of equal magnitude positive and negative voltage supplies, appropriately connected TISP5xxxH3 unidirectional
protectors could replace Th1 and Th2.
4-Wire Digital Systems
A typical system using a two twisted pair connection is the High-bit-rate Digital Subscriber Line (HDSL) and the “S” interface of ISDN.
Figure 12 shows a generic two line system. HDSL tends to have ground referenced protection at both ends of the lines (Th1, Th2, Th3 and Th4).
The ISDN “S” interface is often inside the premises and simple inter-wire protection is used at the terminating adaptor (Th7 and Th8). In all
cases, signal protection, Th5, Th6, Th9 and Th10, can be TISP4015L1 type devices with a 15 V voltage protection level.
AUGUST 1999 - REVISED FEBRUARY 2005
Specifications are subject to change without notice.
Customers should verify actual device performance in their specific applications.
BOURNS [ BOURNS ELECTRONIC SOLUTIONS ]
