Varistor Products
Surface Mount Varistors > SM20 Series
SM20 Varistor Series
Description
The Littelfuse 20mm SMD Series is a surface-mount
metal oxide varistor device, for use in applications
requiring hi-energy / transient current capability.
The AC rated parts are designed to operate
continuously across AC power lines. The DC rated
parts are suitable for Automotive applications. The
series comprises a Nylon molded package with folded
tin plated metal leads for soldering to board.
The SMD Series is based on radial 20mm internal
varistor element with similar characteristics to
the Littelfuse LA / ZA series of varistors.
Agency Approvals
Features
Agency File Number
E320116
•
DC Voltage
Rating 26VDC
•
AC Voltage Rating
175 - 320AC
•
No De-Rating up
to 85°C ambient
•
Lead-Free, HalogenFree and RoHS
Compliant
•
Low voltage
devices specified
for automotive load
dump energy
•
Available in "waffle"
tray packaging
Absolute Maximum Ratings
• For ratings of individual members of a series, see Device Ratings and Specifications chart
Continuous
SM20 Series
Units
20 to 320
V
26
V
up to 6500
A
Steady State Applied Voltage:
AC Voltage Range (VM(AC)RMS)
DC Voltage Range (VM(DC))
Transients:
Peak Pulse Current (ITM) 8/20μs Current Wave, Single Pulse
Single Pulse Energy Capability (WTM) 10/1000μs Current Wave
165
J
Load Dump Energy Capability (td>=30ms)
160
J
Operating Ambient Temperature Range (TA)
-40 to +85
O
Storage Temperature Range (TSTG)
-55 to +125
O
C
C
Temperature Coefficient (aV) of Clamping Voltage (VC) at Specified Test Current
SM20 Series
SM20 Series Ratings & Specifications
Maximum Rating (85°C)
Continuous
Transient
VRMS
VDC
VM(AC)
VM(DC)
(V)
(V)
Part
Number
Branding
V26SM20
26SM20
20
26
V175SM20
V230SM20
V250SM20
V275SM20
V300SM20
V320SM20
175SM20
230SM20
250SM20
275SM20
300SM20
320SM20
175
230
250
275
300
320
225
300
330
369
405
420
Energy
Peak Current
10 x 1000μs
8 x 20μs
WTM
ITM
1x pulse
1x pulse
(J)
20
160 (note 1)
90
122
130
140
165
150
(A)
Specifications (25°C)
Maximum
Varistor Voltage
Clamping
at 1mA DC
Voltage
Test Current
8 x 20 μs
VNOM Min VNOM Max
(V)
32
(10mA)
247
324
354
389
420
462
2000
6500
6500
6500
6500
6500
6500
(V)
40
(10mA)
303
396
429
473
517
540
Typical
Capacitance
f = 1MHz
VC
IPK
C
(V)
(A)
(pF)
63
20
12000
455
595
650
710
775
810
100
100
100
100
100
100
1400
1100
1000
900
800
750
1. Energy rating for impulse duration of 30ms minimum to one half of peak current (automotive load dump).
Peak Current, Energy and Power Derating Curve
Repetitive Surge Capability
For applications exceeding 85ºC ambient temperature, the peak
surge current and energy ratings must be reduced as shown below
V175SM20 - V320SM20
10,000
1
5,000
SURGE CURRENT (A)
90
PERCENT OF RATED VALUE
10
2,000
100
80
70
60
50
40
30
1,000
500
MODEL SIZE 20mm
V175SM20 - V320SM20
10 2 3
10
10 4
10 5
10 6
200
100
50
20
INDEFINITE
10
5
20
2
10
0
-55
2
1
50
60
70
80
90
100
110
120
130
140 150
AMBIENT TEMPERATURE ( oC)
20
100
1,000
IMPULSE DURATION (μs)
10,000
PERCENT OF PEAK VALUE Test
Peak Pulse Current Test Waveform for Clamping Voltage
O1
100
50
0
t
TIM E
t1
t
01 = Virtual Origin of Wave
T = Time from 10% to 90% of Peak
T1 = Rise Time = 1.25 x T
T2 = Decay Time
Example - For an 8/20 μs Current Waveform:
8μs = T1 = Rise Time
20μs = T2 = Decay Time
©2010 Littelfuse, Inc.
SM20 Series Varistor
Revision: May 11, 2010
Specifications are subject to change without notice.
Please refer to www.littelfuse.com/series/sm20.html for current information.
Varistor Products
Surface Mount Varistors > SM20 Series
Lead (Pb) Soldering Recommendations
The principal techniques used for the soldering of
components in surface mount technology are IR Re-flow
and Wave soldering. Typical profiles are shown on the right.
Reflow Solder Profile
250
The terminals of SM20 series devices are tin plated copper,
and the recommended solder is 62/36/2 (Sn/Pb/Ag), 60/40
(Sn/Pb) or 63/37 (Sn/Pb). Littelfuse also recommends an
RMA solder flux.
TEMPERATURE °C
Wave soldering is the most strenuous of the processes.
To avoid the possibility of generating stresses due to
thermal shock, a preheat stage in the soldering process
is recommended, and the peak temperature of the solder
process should be rigidly controlled.
40-80
SECONDS
ABOVE 183°C
150
RAMP RATE
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