Metal Oxide Varistors (MOVs)
LST Varistor Series > SPD Thermally Protected Varistor
© 2021 Littelfuse, Inc.
Specifications are subject to change without notice.
Revised: 02/18/21
LST Varistor Series
Agency Approvals
Applications
Description
Features
Benefits
RoHS
• Type 1 and Type 2 Surge Protective Devices (SPDs)
Agency Standard Agency File Number
UL1449 E320116
The LST Varistor Series is constructed with Littelfuse’s
renowned thermally protected varistor technology (TMOV).
The built-in thermal disconnecting function and electric arc
shield prevent catastrophic failure and fire hazard even under
the extreme circumstances of varistor end-of-life or abnormal
overvoltage conditions. It is specifically designed as a Type 1
Component Assembly Surge Protective Device (SPD) and is
suitable for Type 1 and Type 2 SPDs.
• Short Circuit Current Rating (SCCR) of 200 kA and
Nominal Discharge Current Rating (I
n
) of 20 kA
• Available in both Maximum Discharge Current (I
max
) ratings
of 50 kA and 75 kA. Both ratings utilize the same footprint
and PCB layout
• Mechanically triggered AC and DC rated micro-switch with
Normally Open or Normally Closed options for remote
indication and/or monitoring circuit
• Visual tab option to display LST working status
• RoHS compliant, Lead-free, and Halogen-free
• UL Recognized to UL 1449 and CSA C22.2 No. 269.4 as a
Type 1 Component Assembly (Type 1CA)
• Suitably rated for Type 1 and 2 SPD applications
• Same PCB layout/design for 50 kA and 75 kA I
max
rated SPDs
• More flexibilities/options for designing an isolated remote
indication/monitoring circuit
• Clear indication for technician/engineer to replace EOL
product to continue surge protection for the end product
• Environment-friendly
• Facilitate meeting UL 1449 or CSA C22.2 No. 269.1 and
269.2 for Type 1 or Type 2 SPDs
Typical Circuit Diagram with Normally Open Switch
General Technical Specification
Standard Units
Climatic Category IEC 60068-1 40/85/56
Operating Temperature IEC 61051-1 -40° C ~ +85° C
Storage Temperature -40° C ~ +85° C
Voltage Proof IEC 61051-1 ≥ 2.5 kVRMS
Insulation Resistance IEC 61051-1 ≥ 100 MΩ
To Protected Device
Power
Source
Thermal
Disconnector
Metal Oxide Varistor
(MOV)
C (Common)
NO (Normally Open)
Thermal
Connection Isolation
Primary Side
Contact Lead
MOV Lead
Galvanic Isolation
Secondary Side
Note:
This typical circuit shows how the switch pins (C and NO) can be used to indicate the
connection status of thermal disconnector for remote indication. This denotes that the circuit
will be no longer protected from surge currents by the MOV after the thermal disconnector
forms open circuit.
Pb
Metal Oxide Varistors (MOVs)
LST Varistor Series > SPD Thermally Protected Varistor
© 2021 Littelfuse, Inc.
Specifications are subject to change without notice.
Revised: 02/18/21
Switch Function Configuration
Note:
For LST***7 device with I
max
75 kA rating, thermal disconnector may safely open circuit without any damage to the device after I
max
test.
Electrical Specifications
Part Number
Specifications (85° C) Specifications (25° C)
Maximum Continuous
Operating Voltage
(MCOV)
Peak Surge Current
(8/20 μs, 1 Pulse)
Nominal
Discharge
Current
(8/20 μs,
15 Pulses)
Voltage
Protection
Rating
Maximum
Short Circuit
Current Rating
V
RMS
I
max
I
n
VPR SCCR
( V ) ( kA ) ( kA ) ( V ) ( kA )
LST1505VL2NT1 150 50 20 600 200
LST1507VL2NT1 150 75 20 600 200
LST1805VL2NT1 180 50 20 800 200
LST1807VL2NT1 180 75 20 800 200
LST2755VL2NT1 275 50 20 900 200
LST2757VL2NT1 275 75 20 900 200
LST3205VL2NT1 320 50 20 1000 200
LST3207VL2NT1 320 75 20 1000 200
LST3855VL2NT1 385 50 20 1500 200
LST3857VL2NT1 385 75 20 1500 200
LST4205VL2NT1 420 50 20 1500 200
LST4207VL2NT1 420 75 20 1500 200
LST5105VL2NT1 510 50 20 1500 200
LST5107VL2NT1 510 75 20 1500 200
LST5505VL2NT1 550 50 20 1500 200
LST5507VL2NT1 550 75 20 1500 200
LST6905VL2NT1 690 50 20 2000 200
• Normally-open and/or normally-closed switch functions are available for remote indication circuit to identify LST
working status
• Switch pins of Common (“C”) and Normally-Open (“NO”) can be connected together for normally-open monitoring circuit
• Switch pins of Common (“C”) and Normally-Closed (“NC”) can be connected together for normally-closed monitoring circuit
• Electrical rating for switch pin: 60 Vdc/0.2 A, or 250 Vac/0.1 A
• “Visual Tab” within housing: LST is still functional
• “Visual Tab” shows up (Optional): LST has been activated and needs to be replaced
Switch Functions Switch Pins Connected to Signal Circuit
Normally Open C and NO
Normally Closed C and NC
Normally Open &
Normally Closed
C and NO: Normally Open monitoring circuit
C and NC: Normally Closed monitoring circuit
No Function No switch pin