TISP4070L3BJ, TISP4350L3BJ
BIDIRECTIONAL THYRISTOR OVERVOLTAGE PROTECTORS
AUGUST 1999 — REVISED NOVEMBER 1999
FLOW
COMMENT
boxes G and H
Fail
The criterion for box G is a fire enclosure and spacings (See box D
comments).
Y
Y
G
A yes result passes the equipment and a no result leads to box H.
N
The criterion for box H is to pass Tests 2, 3 and 4. Test 2 is not required
if there is overcurrent protection that reduces currents above 1.3 A
(See box C).
Pass
H
N
High performance modems, using fuses and without fire enclosures,
must pass tests 2, 3, possibly 3A if the fuse opens, and 4. For standard
modems, using fuses of 1 A or less and without fire enclosures, tests
3, 3A and 4 must be passed.
If the two pass criteria of each of the tests performed are met, this is a
yes and the equipment passes.
A no result fails the equipment.
fuse values
There are two areas of fuse criteria; surge capability (FCC Part 68 impulse) and power cross capability
(UL1950 clause 6.6 and annex NAC).
To survive an impulse, a fuse must have a melting I2t rating greater than the impulse I2t. The fuse I2t rating
should be specified for the impulse waveshape current as the normal d.c. rating may not result in adiabatic
conditions. Alternatively, the fuse may be specified for a rated current under the impulse waveshape
conditions.
An exponentially decaying impulse with a current amplitude IPP and 50 % amplitude decay time of tD has an
I2t value of 0.72IPP2tD. Test waveforms have tolerences and the formula can be approximated to IPP2tD, giving
about an 40 % allowance to cover tolerences e.g. +5 % on IPP and +30 % on tD. Using the approximate
formula, the I2t values for typical waveforms are shown in the table below.
2
AMPLITUDE I
CURRENT WAVESHAPE
t /t (µs)
MELTING I t
PP
SPECIFICATION
2
A
A s
R
D
200
100
37.5
37.5
500
100
10/160
10/560
5/320
6.4
5.6
FCC Part 68, Type A
FCC Part 68, Type B
UL 1950 / ITU-T K21
0.45
0.45
2.5
5/310
TELCORDIA (FORMALLY BELLCORE)
GR-1089
2/10
10/1000
10
Fuse power cross current capability can be determined from it’s time-current curve. The fuse must be rated to
break the current at the applied power cross a.c. voltage level.
fuse values for FCC Part 68
Fuses must not blow on the Type B surge. To survive a 37.5 A Type B surge, the fuse needs to have an I2t of
greater than 0.45 A2s. Fuses, such as the 1 A surface mount SMTelecom™ 0436001.PR or the 0.5 A axial
lead 2AG Surge Withstand 230.500 (both from the Littelfuse) will meet this criteria.
P R O D U C T
I N F O R M A T I O N
9
POINN [ POWER INNOVATIONS LTD ]
