The Tool Desk
Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Outbyte Driver Updater FREEFix the driver behind crashes, sound loss and screen glitchesFind Drivers →RF0323-000 is a Littelfuse surface-mount resettable PPTC fuse, not a varistor. Its series designation is SMD030F-2018; the manufacturer lists a 0.30 A hold current, 0.80 A trip current and 60 V DC maximum voltage. It protects against overcurrent, not voltage surges. Use the manufacturer’s datasheet and mechanical drawing to check fit and circuit suitability.
RF0323-000 specifications
The figures below are the published ratings for RF0323-000 / SMD030F-2018 in Littelfuse’s PolySwitch SMD datasheet. They are not a substitute for checking the datasheet’s conditions, curves and current revision.
| Parameter | Published value |
|---|---|
| Ordering part number | RF0323-000 |
| Series designation | SMD030F-2018 |
| Package family | midSMD 2018 |
| Hold current (IH) | 0.30 A |
| Trip current (IT) | 0.80 A |
| Maximum voltage (VMAX) | 60 V DC |
| Maximum fault current (IMAX) | 20 A |
| Maximum power dissipation (PD,MAX) | 1.50 W |
| Maximum time to trip | 1.50 s at the datasheet’s stated test condition |
| Minimum resistance (RMIN) | 0.500 Ω |
| Maximum post-trip resistance (R1MAX) | 2.30 Ω |
Littelfuse identifies the product page as SMD030F-2018-2 and lists RF0323-000 as its ordering code. See the Littelfuse product page.
What the device does—and what it does not do
A polymeric positive-temperature-coefficient (PPTC) device carries current with relatively low resistance in normal operation. Excessive current heats the element, causing its resistance to rise sharply and limit current. Once the fault is removed and the part cools, it can return toward its normal low-resistance state. It is resettable, but it does not necessarily restore immediately while a fault remains.
#1 Best Overall
- Minimum Operating Temperature: - 40 C Maximum Operating Temperature: + 125 C Lead Spacing: 10.75 mm
RF0323-000 is for overcurrent protection. It is not a metal-oxide varistor (MOV), TVS diode, or voltage-clamping surge suppressor. A varistor or TVS addresses voltage transients; a PPTC responds to current-related heating. A circuit exposed to both faults may need coordinated overcurrent and transient protection.
- Compared with a one-time fuse: a PPTC can recover after cooling, while a conventional fuse is intended to open and require replacement. Their resistance, response, fault-clearing behavior and approvals differ.
- Compared with an active current limiter or circuit breaker: a PPTC is thermally operated, so its response depends on current and heat dissipation; it is not a precise electronic current regulator.
How to interpret the electrical ratings
Hold current and trip current
The 0.30 A hold current is the specified current the device can carry without tripping under the datasheet’s stated conditions. The 0.80 A trip current is a specified trip characteristic under its test conditions; it is not a promise of an instantaneous, universal threshold. Ambient temperature, PCB copper and heat sinking, nearby heat sources, assembly and overload duration all affect in-circuit behavior. Keep continuous current below the temperature-adjusted hold capability rather than designing at the 0.30 A label alone.
Startup surges from capacitor charging, motors, lamps or converters can cause nuisance trips even if steady-state load current is acceptable. Evaluate the actual startup waveform and consult the manufacturer’s time-current curves.
Maximum voltage and fault current
The 60 V DC maximum is an operating voltage limit for the PPTC, not a surge-clamping level, a voltage regulation point or an isolation rating. Check normal supply limits, transients, available fault current and the voltage and energy the device may experience while tripped. Do not treat this part as sole protection for high-energy mains or other fault sources without evaluating the complete application and applicable safety requirements.
The datasheet’s 20 A maximum fault-current entry is condition-dependent; it is not a universal interruption or breaking-capacity rating. Assess source impedance, voltage, short-circuit current, fault duration and board construction together. A secondary fuse or current-limited source may be necessary.
Resistance, voltage drop and heating
The listed resistance range matters in low-voltage designs. Using Ohm’s law at 0.30 A, 0.500 Ω corresponds to about 0.15 V drop and 0.045 W dissipation; 2.30 Ω corresponds to about 0.69 V and 0.207 W. These are calculations from the published resistance values, not guaranteed in-circuit measurements. Resistance varies with temperature, test conditions, age and device state, and may rise after tripping.
Rank #3
- Mounting Style: PCB Mount
- Termination Style: Radial
- Hold Current: 550 mA
- Maximum Voltage: 120 VAC/VDC
- Trip Current: 1.25 A
Check both normal-operation voltage drop and the residual current and voltage after a trip. If a fault persists, the part may remain hot and high-resistance rather than returning promptly to its normal state.
Trip time
Littelfuse lists a maximum time to trip of 1.50 seconds at the stated test current. That is not a fixed response time for every overload. A large short circuit can heat the part quickly; a modest overload may take longer, and the installed board’s thermal conditions affect the result. Choose another protection method if the circuit needs precise or very fast current limiting.
Windows Errors? Fix Them Before They Spread
Repair common Windows errors and clear accumulated junk for a smoother, more stable PC - no reinstall needed.Free scan · no reinstallCrashes, No Sound, or Screen Glitches?
Random freezes, missing sound and display glitches usually trace back to one bad driver. Find and replace yours safely.Free scan · under a minutePackage and PCB fit
The 2018 designation identifies the midSMD package family; do not derive exact body, pad or height dimensions from the name alone. Use Littelfuse’s mechanical drawing and recommended land pattern in the datasheet before laying out a board or approving a replacement. Copper area, nearby heat sources, enclosure temperature and airflow can also change trip behavior and effective hold current.
Rank #4
- Trip Current: 32 A Current Rating - Max: 25 A Resistance: 3.3 mOhms
Is RF0323-000 suitable for a 5 V, 12 V or 24 V circuit?
Those voltages are below the listed 60 V DC maximum, but voltage compatibility alone does not establish suitability. Check the operating and transient voltage, load and startup current, thermal derating, available fault energy, resistance-related drop and required fault response.
- 5 V rails: the resistance-related drop can be a significant share of the supply margin, so calculate it across the relevant resistance range.
- 12 V and 24 V systems: verify supply tolerance and transients as well as the 60 V limit; the device is not a surge suppressor.
- Automotive or industrial power: do not infer application approval from voltage rating alone. Evaluate the circuit’s fault conditions and required safety or qualification standards.
For a first-pass current check, compare maximum continuous load current with the hold current after applying the manufacturer’s temperature and application guidance: I_load,max < I_H,derated. Then evaluate inrush and fault behavior using the datasheet curves; a simple inequality cannot establish complete protection.
Choosing a replacement or nearby Littelfuse part
Search with both RF0323-000 and SMD030F-2018: ordering codes and series designations may differ between catalog records. Littelfuse lists these nearby options in its SMD PPTC datasheet. They are comparison candidates, not confirmed drop-in replacements.
Do these 3 things before closing this tab:
1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteBest Value
- Littelfuse 60R025XU
- Resettable Fuses
- PPTC
- 60V .25A
| Ordering code | Series designation | Hold current | Trip current | Maximum voltage | Key substitution caution |
|---|---|---|---|---|---|
| RF0323-000 | SMD030F-2018 | 0.30 A | 0.80 A | 60 V | Original device |
| RF0324-000 | SMD100F-2018 | 1.10 A | 2.20 A | 15 V | Lower voltage rating |
| RF0325-000 | SMD150F-2018 | 1.50 A | 3.00 A | 15 V | Lower voltage rating |
| RF0326-000 | SMD200F-2018 | 2.00 A | 4.20 A | 6 V | Lower voltage rating |
| RF1342-000 | decaSMDC050F/60 | 0.55 A | 1.10 A | 60 V | Different series; verify package, resistance and thermal behavior |
The higher-current 2018 options have lower voltage ratings, so they cannot be assumed suitable in a circuit that needs the original 60 V capability. RF1342-000 has a different series designation and likewise needs mechanical and electrical validation. The Littelfuse circuit-protection selection guide describes the midSMD 2018 family as covering roughly 0.3–2.0 A hold-current options and gives family-level information; confirm individual-device ratings and derating in its latest datasheet.
Before substituting, verify each of the following against the actual application and manufacturer documentation:
- Package, footprint and assembly/reflow compatibility.
- Hold and trip current at the installed ambient temperature and PCB thermal conditions.
- Maximum working voltage and fault-current capability.
- Initial and post-trip resistance, voltage drop and power dissipation.
- Time-current behavior, recovery behavior and environmental rating.
- Required qualification, RoHS/REACH status, agency requirements and lifecycle suitability.
A similarly labeled hold current does not establish equivalence. A MOV is not a substitute because it serves a different protection function; a one-time fuse is not equivalent when automatic recovery is required. Conversely, choose a one-time fuse when permanent disconnection, fast clearing, low resistance, a high interrupt rating or a specified safety requirement matters more than resettable behavior.
Documentation and sourcing
Use the Littelfuse datasheet for electrical ratings, curves and mechanical information, and the manufacturer product page for product identification. Littelfuse says specifications may change without notice, so confirm the current revision before production release. For purchasing, match the manufacturer part number and series designation and verify region-specific availability, packaging, date code, traceability and compliance with the supplier; no price or stock level is established here.
Recommended Free Tools
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
