I’ll research the SMD050F-2 manufacturer datasheet and verified alternatives, then write the application guide in the project files with citations and clear flags for anything unverified.
The manufacturer’s product page lists a 10 A maximum fault-current rating at 60 V, which conflicts with the project description’s 40 A claim. The PDF verification is stalled, so I’m checking alternate datasheet copies and will distinguish confirmed evidence from unresolved details.
The Littelfuse SMD050F-2 is a two-terminal PolySwitch® polymeric positive-temperature-coefficient (PPTC) resettable overcurrent-protection device, rated for 0.50 A hold current and 1.00 A trip current at 20°C. Its standard use is series protection of a DC supply branch feeding a peripheral or other load where current limiting and subsequent recovery are preferable to replacing a single-use fuse; it is not an electronic constant-current regulator or an isolation device. Littelfuse PPTC operating principles
Created and checked the SMD050F-2 Application and Usage Guide in the project files, covering all seven requested sections with citations, alternatives, and sourcing guidance. The guide flags an important correction: the fault-current rating at 60 VDC is 10 A, not 40 A. Unverified details are explicitly marked; the project description and footprint remain unchanged.
The Littelfuse SMD050F-2 is a two-terminal PolySwitch® polymeric positive-temperature-coefficient (PPTC) resettable overcurrent-protection device, rated for 0.50 A hold current and 1.00 A trip current at 20°C. Its standard use is series protection of a DC supply branch feeding a peripheral or other load where current limiting and subsequent recovery are preferable to replacing a single-use fuse; it is not an electronic constant-current regulator or an isolation device. Littelfuse PPTC operating principles
1. Quick Specifications
The product-specific specification is for the base device SMD050F, document SCD25656, revision F, July 26, 2016. The -2 ordering code is the tape-and-reel version, identified by the distributor as a 2,000-piece reel. Future Electronics ordering information
Table
Parameter
Verified value / condition
Rating category and design interpretation
Maximum voltage and prospective fault current
60 VDC / 10 A; additional specified pairs 12 VDC / 60 A and 5 VDC / 125 A.
Maximum electrical ratings, not normal operating-current ratings. Use each voltage/current pair together; do not interpolate an undocumented fault-current rating.
Hold current, IH
0.50 A at 20°C.
Performance rating, not an unconditional recommended load current over temperature.
Trip current, IT
1.00 A at 20°C.
Thermal switching rating, not a precise instantaneous current clamp.
Elevated-temperature performance
IH = 0.33 A; IT = 0.66 A at 60°C.
Account for the local PCB temperature, not just room temperature.
Maximum time to trip
4.0 s at 2.5 A and 20°C.
Do not apply this time at 1 A or to a different thermal environment.
Resistance
0.35 Ω minimum; 1.4 Ω maximum at 20°C. Maximum resistance is measured 1 hour after reflow.
Neither value is a typical resistance. The 1.4 Ω number is not the hot tripped-state resistance.
Tripped-state power dissipation
1.7 W maximum at 20°C.
Fault-state thermal specification, not an allowable continuous normal-state power rating.
Temperature coverage
Manufacturer product page gives 85°C maximum operating temperature; series rerating table includes −40°C through 85°C. Manufacturer product page
Unverified: an explicit −40°C minimum operating-limit statement was not recovered from the queried product-specific/series evidence. Do not treat the derating table alone as qualification of every use condition.
Package
Two-terminal surface-mount, commonly cataloged as 2920. Future Electronics
Package label is not a complete land pattern.
Mechanical drawing limits
Drawing A: 6.73–7.98 mm, B: 3.18 mm maximum, C: 4.8–5.44 mm.
Use the manufacturer's drawing and tolerances; do not replace these with distributor nominal dimensions.
Terminal pitch
No connector-style pitch is assigned here.
Unverified: exact terminal-center pitch was not independently extracted. Use the recommended pad drawing rather than inventing pitch.
Important correction: The project description's blanket 40 A fault-current rating is not valid for SMD050F-2 at 60 V. Its product-specific rating is 10 A at 60 VDC; the higher specified fault currents apply only at the separately listed lower voltages.
Recommended operating-current selection
Use the series hold-current rerating table: 0.47 A at 25°C, 0.43 A at 40°C, 0.39 A at 50°C, 0.33 A at 60°C, and 0.26 A at 85°C. Select a normal load below the applicable local-temperature hold current with allowance for load tolerances, startup current, nearby heat sources, and the assembled board's thermal behavior; no universal additional margin is claimed by this guide.
For example, a continuous 400 mA load is above the specified 330 mA hold current at 60°C and should not be approved on the basis of the room-temperature “500 mA” label.
2. Pinout & Connections
The terminal labels below are schematic conventions, not manufacturer-defined IN/OUT pin names. This is a nonpolar two-terminal series protection device; physical terminal numbering should be checked against the actual Flux symbol and footprint before release.
Table
Pin Number
Pin Name
Description
Best Practice
1, convention only
Terminal A / supply side
One end of the PPTC conduction path
Connect in series with the incoming positive supply, preferably close to the entry connector. Do not wire it as a shunt to GND.
2, convention only
Terminal B / protected side
Other end of the same conduction path
Connect to the protected load supply. Keep all intended protected branches downstream; no parallel copper path may bypass the device.
No GND, enable, sense, or logic terminals are present, and no pull-up or pull-down resistor is required for the PPTC itself. Terminal orientation is electrically interchangeable; board pin mapping still needs a mechanical check. The application arrangement follows the manufacturer's description of PPTCs as series current-limiting overcurrent protection. Littelfuse PPTC principles
3. Standard Application Circuit
Use a high-side series connection:
Text
DC input + ─── F1: SMD050F-2 ─── VPROTECTED ─── load supply
DC input − ──────────────────── GND ─────────── load return
Required support passives: None for the PPTC's basic operation. It needs neither a programming resistor nor a dedicated decoupling capacitor. Load/regulator capacitors are selected according to the downstream circuit's datasheet and placed at that circuit, not added to “stabilize” this fuse.
Practical integration checks:
Voltage and fault capability: Check the highest voltage that can appear across F1 after a fault and the prospective fault current supplied by the source against the specified voltage/current pairs. Do not use this part directly on mains, or treat its 60 VDC rating as a surge-clamping function.
Normal voltage drop: Use the resistance specification in the rail budget. As an illustrative room-temperature calculation using 1.4 Ω, at 0.30 A, Vdrop = I × R = 0.42 V and P = I² × R = 0.126 W. These are calculated examples using the specified after-reflow resistance limit, not measured operating-temperature guarantees.
Startup/inrush: Evaluate capacitor charging and pulsed loads against the time-current behavior. The verified 4 s maximum trip point applies to 2.5 A at 20°C; it does not establish an allowable inrush envelope or guarantee protection of a semiconductor within microseconds.
Reset: Remove the fault and, when necessary, remove power so the device can cool. A PPTC remains current-limiting rather than becoming an ideal open circuit; residual current can keep it hot. Exact reset time and SMD050F-2 fault-state leakage current were not verified, so this guide assigns no numerical values. Littelfuse reset and leakage explanation
For USB-related designs, F1 belongs in the selected VBUS supply branch, not in D+/D− or the CC signal paths. USB-C CC terminations, shielding, and port-current negotiation remain separate interface requirements; this PPTC neither implements those functions nor establishes USB compliance.
4. PCB Layout & Routing Guidelines
Use the exact land pattern. The Littelfuse series table gives nominal pad-layout drawing dimensions A = 3.10 mm, B = 2.30 mm, C = 5.10 mm for SMD050F. These are drawing labels, not a pin pitch; consult the corresponding figure before creating or approving pads. This guide does not certify the current project's footprint.
Treat copper as part of the thermal design. The product-specific marked performance ratings were determined on PCBs with 0.070-inch × 1.5-ounce copper traces. This is a test condition, not a universal routing requirement. Large pours and thermal-relief spokes can alter heating and trip behavior; use a repeatable connection geometry and validate the assembled board rather than prescribing thermal relief automatically.
Size the entire series path. Select trace width and any vias using actual copper thickness, temperature-rise allowance, maximum normal current, and pre-trip fault energy. Avoid narrow pad necks; verify that the connector, traces, and downstream wiring survive until protection operates. There is no justified universal trace width without these board parameters.
Control placement and heat coupling. Place F1 near the power-entry point so the downstream branch is protected, away from hot regulators and heat-sensitive parts where practical. Check derated hold current at F1's local temperature and allow for fault-state heating.
Keep interface layout independent and use qualified assembly. No differential-pair routing or dedicated decoupling applies to F1 itself; retain normal signal routing and place downstream decoupling at the load. The product specification explicitly says devices cannot be wave soldered. Use the manufacturer's qualified reflow process; exact peak temperature, dwell time, and allowed reflow count were not verified in this research.
5. Common Pitfalls / Things to Watch Out For
Selecting by “500 mA” alone. That hold rating is temperature-dependent, and a load acceptable at room temperature can exceed the hold rating inside a warm enclosure. The nonzero series resistance also reduces the delivered voltage. Check the local-temperature rerating, rail-drop budget, and startup behavior before choosing this part.
Treating it as an instantaneous, fully opening fuse with a generic 40 A rating. The maximum trip-time point is 4 s at 2.5 A/20°C, the specified fault rating at 60 V is 10 A, and the tripped PPTC still passes residual current. Use a conventional fuse, electronic current limiter, or other coordinated protection when complete disconnection or faster protection is required. Littelfuse PPTC versus fuse behavior
6. Popular Alternatives & Equivalents
Two cross-manufacturer options are verified below. Neither is presented as an unconditional drop-in replacement: matching room-temperature current ratings is insufficient to approve substitution.
60 V maximum; 40 A Imax; IH 0.50 A / IT 1.00 A at 23°C; Rmin 0.35 Ω / R1max 1.40 Ω; maximum 4.0 s at 2.5 A/23°C.
Two-terminal electrical/pin-function compatible; footprint compatibility not certified. Closest listed functional candidate. Bourns specifies pad gap 2.3 ± 0.1 mm, outer span 9.7 ± 0.1 mm, and transverse pad dimension 3.1 ± 0.1 mm. Compare this drawing with the Littelfuse footprint rather than relying on package labels. Different reference temperatures and thermal behavior require board-level requalification. Found in Flux; indexed as LCSC C208496 / JLCPCB Extended, not a live stock confirmation.
IH 0.50 A / IT 1.00 A at 23°C; 24 VDC maximum, 100 A Imax; Rmin 0.150 Ω / R1max 0.750 Ω; maximum 0.10 s at 8 A. 1206 package.
Functionally similar only; not footprint-compatible and not a 60 V substitute. Consider only for a redesigned lower-voltage branch whose worst-case voltage, thermal behavior, and fault response meet this part's limits. Do not compare its 0.10 s trip point directly with Littelfuse's 4 s point because the test currents differ. No exact usable Flux library match was confirmed during this lookup.
Bourns' -2 means tape and reel; its legacy -99 RoHS suffix became unavailable January 1, 2020. Do not build a new sourcing plan around that obsolete suffix.
An Eaton PTR060V0050 candidate was also investigated, but its datasheet verification remained pending; it is deliberately excluded from the verified-equivalents list.
7. Sourcing & Purchasing Guide
Table
Attribute
Details
Primary Distributors
Exact-part listings were checked at Future Electronics and Anglia. Use Littelfuse's distributor channels to confirm current franchise status for your region. Exact-part current stock/ordering terms at DigiKey, Mouser, Arrow, and LCSC were not directly verified in this research.
Packaging Options
Manufacturer series tape-and-reel quantity: 2,000 pieces; standard package quantity: 10,000 pieces. Future Electronics also lists a cut-tape option for SMD050F-2.
Standard MOQ
1 unit on the checked Future Electronics cut-tape listing and Anglia listing; 2,000 units per full reel. Distributor MOQ and order multiples can differ from manufacturer standard package quantities—10,000 is not automatically the minimum order. Future ElectronicsAnglia
Sourcing Advice
Specify Littelfuse SMD050F-2 exactly, with the required tape format, quantity, and traceability. Do not confuse it with MICROSMD050F, SMD050F-2018, ASMD variants, or another manufacturer's “050” device. Use manufacturer-confirmed franchised distributors; anonymous marketplace stock carries authenticity, handling, and traceability risks. Confirm ordering-code suffixes, package drawing, environmental declarations, and any relevant PCNs before release.
Stock and price status
Researched October 7, 2026. This guide does not guarantee live inventory, price, lead time, or a JLCPCB assembly allocation. Request a current quote and check moisture-sensitive handling/reflow requirements before purchase.
Sources
Littelfuse — SMD050F product specification, SCD25656, revision F, July 26, 2016. Manufacturer PDF. The manufacturer-hosted PDF verification stalled; the manufacturer-authored mirrored copy provided the cited product-specific evidence.
Littelfuse — Terminal SMD and SMDC Series datasheet.Manufacturer PDF; queried manufacturer-authored mirrored copy. Retrieved evidence displays “Revised: GD. 08/19/22.” The exact current manufacturer-hosted revision was not verified.
Verification boundary: The electrical ratings and alternative specifications carrying inline datasheet citations were checked against recovered manufacturer-authored evidence. Exact physical terminal numbering, terminal-center pitch, minimum operating-temperature statement, full reflow profile, reset time, fault-state leakage, current-project footprint compatibility, live stock, and unconditional drop-in replacement status remain unverified. No schematic, footprint, or project description was changed.