w w w . l i t t e l f u s e . c o m
51
The electrical characteristics of a SMT100 device are similar to
that of a self-gated Triac, but the SMT100 is a two terminal
device with no gate. The gate function is achieved by an
internal current controlled mechanism.
Like the T.V.S. diodes, the SMT100 has a standoff voltage
(Vrm) which should be equal to or greater than the operating
voltage of the system to be protected. At this voltage (Vrm)
the current consumption of the SMT100 is negligible and will
not affect the protected system.
When a transient occurs, the voltage across the SMT100 will
increase until the breakdown voltage (Vbr) is reached. At this
point the device will operate in a similar way to a T.V.S.
device and is in avalanche mode.
The voltage of the transient will now be limited and will only
increase by a few volts as the device diverts more current. As
this transient current rises, a level of current through the
device is reached (Ibo) which causes the device to switch to a
fully conductive state such that the voltage across the device
is now only a few volts (Vt). The voltage at which the device
switched from the avalanche mode to the fully conductive
state (Vt) is known as the Breakover voltage (Vbo). When the
device is in the Vt state, high currents can be diverted
without damage to the SMT100 due to the low voltage across
the device, since the limiting factor in such devices is
dissipated power (V x I).
Resetting of the device to the non-conducting state is
controlled by the current flowing through the device. When
the current falls below a certain value, known as the Holding
Current (Ih), the device resets automatically.
As with the avalanche T.V.S. device, if the SMT100 is subjected
to a surge current which is beyond its maximum rating, then
the device will fail in short circuit mode, ensuring that the
equipment is ultimately protected.
ELECTRICAL CHARACTERISTICS
SELECTING A SMT100
COMPLIES WITH THE
PEAK SURGE
VOLTAGE
CURRENT
ADMISSIBLE IPP
NECESSARY
FOLLOWING STANDARDS
VOLTAGE
WAVEFORM
WAVEFORM
RESISTOR
(V)
(
S)
(
S)
(A)
(CCITT) ITU-K20
1000
10/700
5/310
25
-
(CCITT) ITU-K17
1500
10/700
5/310
38
-
-
VDE0433
2000
10/700
5/310
50
VDE0878
2000
1.2/50
1/20
50
-
IEC-1000-4-5
10/700
5/310
50
-
level 4
1.2/500
8/20
100
-
FCC Part 68, lightning surge
1500
10/160
10/160
75
12.5
type A
800
10/560
10/560
55
6.5
FCC Part 68, lightning surge
1000
9/720
5/320
25
-
type B
Bellcore TR-NWT-001089
2500
2/10
2/10
150
11.5
first level
1000
10/1000
10/1000
50
10
Bellcore TR-NWT-001089
5000
2/10
2/10
150
11.5
second level
CNET I31-24
1000
0.5/700
0.8/310
25
-
level 3
V
R
V
BR
V
RM
V
BO
I
RM
I
BO
I
H
I
pp
I
V
1. When selecting a SMT100 device, it is important
that the Vrm of the device is equal to or greater than
the the operating voltage of the system.
2. The minimum Holding Current (Ih) must be greater
than the current the system is capable of delivering
otherwise the device will remain conducting
following a transient condition.
V-I Graph illustrating symbols
and terms for the SMT100
surge protection device
SMT100
52
w w w . l i t t e l f u s e . c o m
SMT100
Note 1: Measured @ 1V bias, 1M
HZ.
All parameters are tested using a FET TEST
TM
model 3600.
ELECTRICAL CHARACTERISTICS (Tamb 25C)
ABSOLUTE MAXIMUM RATINGS (Tamb 25C)
THERMAL RESISTANCE
SYMBOL
PARAMETER
SYMBOL
PARAMETER
V
RM
Stand-off Voltage
V
RO
Breakover Voltage
I
RM
Leakage Current at Stand-off Voltage
I
H
Holding current
V
R
Continuous Reverse Voltage
I
BO
Breakover Current
V
BR
Breakdown Voltage
I
PP
Peak pulse Current
C
Capacitance
I
R
Continuous Reverse Current
SYMBOL
PARAMETER
VALUE
UNIT
R
TH
(J-I)
Junction to leads
20
C/W
R
TH
(J-I)
Junction to ambient on printed circuit
100
C/W
(with standard footprint dimensions)
SYMBOL
PARAMETER
VALUE
UNIT
I
PP
Peak pulse Current:
10/1000S (open circuit voltage waveform 1kV 10/1000S)
100
A
5/310S (open circuit voltage waveform 4kV 10/700S)
150
A
8/20S (open circuit voltage waveform 4kV 1.2/50S)
250
A
2/10S (open circuit voltage waveform 2.5kV 2/10S)
500
A
I
TSM
Non-repetitive surge peak on-state current
50Hz
55
A
F = 50Hz
60Hz
60
A
Non-repetitive surge peak on-state current
0.2s
25
A
F = 50Hz
2s
12
A
T
L
Maximum lead temperature range
260
C
T
stg
Storage temperature range
-55 to +150
C
T
j
Maximum junction temperature
150
C
Type
SMT100-35
SMT100-65
SMT100-120
SMT100-140
SMT100-200
SMT100-230
SMT100-270
Marking
Laser
B035
B065
B120
B140
B200
B230
B270
I
RM
@ V
RM
MAX
(A)
(V)
I
RM
@ V
R
MAX
(A)
(V)
35
65
120
140
200
230
270
50
50
50
50
50
50
50
800
800
800
800
800
800
800
55
80
160
200
265
300
350
32
55
110
120
170
200
230
2
2
2
2
2
2
2
V
BO
@ I
BO
MAX
(V)
(mA)
I
H
MIN
(Note 1)
(mA)
150
150
150
150
150
150
150
C
MAX
(pF)
180
160
140
140
130
120
120
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