SMT50
ELECTRICAL CHARACTERISTICS
The electrical characteristics of a SMT50 device are similar to
that of a self-gated Triac, but the SMT50 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 SMT50 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 SMT50 is negligible and will
not affect the protected system.
Resetting of the device to the non-conducting state is
When a transient occurs, the voltage across the SMT50 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.
As with the avalanche T.V.S. device, if the SMT50 is subjected
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
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.
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.
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 SMT50 due to the low voltage across
the device, since the limiting factor in such devices is
dissipated power (V x I).
SELECTING A SMT50
1. When selecting a SMT50 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 SMT50 surge
protection device.
I
BO
I
H
I
RM
V
RM
V
BR
V
BO
V
R
V
I
pp
I
COMPLIES WITH THE
FOLLOWING STANDARDS
PEAK SURGE
VOLTAGE
(V)
VOLTAGE
WAVEFORM
(
µS)
10/700
10/700
10/700
1.2/50
10/700
1.2/500
10/160
10/560
9/720
2/10
10/1000
2/10
0.5/700
CURRENT
WAVEFORM
(
µS)
5/310
5/310
5/310
1/20
5/310
8/20
10/160
10/560
5/320
2/10
10/1000
2/10
0.8/310
ADMISSIBLE
IPP
NECESSARY
RESISTOR
(
Ω
)
-
-
-
-
-
-
12.5
6.5
-
11.5
10
11.5
-
(A)
25
38
50
50
50
100
75
55
25
150
50
150
25
(CCITT) ITU-K20
(CCITT) ITU-K17
VDE0433
VDE0878
IEC-1000-4-5
FCC Part 68, lightning surge
type A
FCC Part 68, lightning surge
type B
Bellcore TR-NWT-001089
first level
Bellcore TR-NWT-001089
second level
CNET
I31-24
1000
1500
2000
2000
level 3
level 4
1500
800
1000
2500
1000
5000
1000
48
w w w. l i t t e l f u s e . c o m
SMT50
ELECTRICAL CHARACTERISTICS (Tamb 25°C)
SYMBOL
V
RM
I
RM
V
R
V
BR
C
PARAMETER
Stand-off Voltage
Leakage Current at Stand-off Voltage
Continuous Reverse Voltage
Breakdown Voltage
Capacitance
SYMBOL
V
BO
I
H
I
BO
I
PP
PARAMETER
Breakover Voltage
Holding Current
Breakover Current
Peak pulse Current
THERMAL RESISTANCE
SYMBOL
R
TH
(J-I)
R
TH
(J-I)
PARAMETER
Junction to leads
Junction to ambient on printed circuit
(with standard footprint dimensions)
VALUE
20
100
UNIT
°
C/W
°
C/W
ABSOLUTE MAXIMUM RATINGS (Tamb 25°C)
SYMBOL
P
I
PP
PARAMETER
Power dissipation
Peak pulse current
T
lead
10/1000µS
8/20µS
I
TSM
dV/dt
T
stg
T
j
T
L
Non repetitive surge peak on-state current
Critical rate of rise of off-state voltage
Storage temperature range
Maximum junction temperature
Maximum lead temperature for soldering during 10s
tp + 20ms
V
RM
VALUE
5
50
100
30
5
-55 to +150
150
260
UNIT
W
A
A
A
KV/µS
°
C
°
C
T
stg
Type
Marking
I
RM
@ V
RM
MAX
(µA)
2
2
2
2
2
2
2
2
2
2
(V)
56
60
90
180
117
162
180
198
216
243
I
RM
@ V
R
MAX
(µA)
50
50
50
50
50
50
50
50
50
50
(V)
62
68
100
120
130
180
200
220
240
270
V
BO
@
I
BO
MAX
(V)
82
90
133
160
173
240
267
293
320
360
(mA)
800
800
800
800
800
800
800
800
800
800
I
H
MIN
(Note 1)
C
MAX
(pF)
150
150
100
100
100
100
100
100
100
100
Laser
SMT50-62
SMT50-68
SMT50-100
SMT50-120
SMT50-130
SMT50-180
SMT50-200
SMT50-220
SMT50-240
SMT50-270
A062
A068
A100
A120
A130
A180
A200
A220
A240
A270
(mA)
150
150
150
150
150
150
150
150
150
150
All parameters are tested @ 25
°
C except where indicated.
Note 1: Measured @ 1V bias, 1M
HZ
All parameters are tested using a FET TEST model 3600
TM
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49
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