Introduction (data-driven hook)
Engineers expect polymeric PTC resettable fuses to exhibit predictable hold vs. trip currents, defined voltage ratings, and characteristic time‑to‑trip curves that span milliseconds to minutes depending on overload magnitude. This report distills the device’s critical electrical, thermal and application data from the official datasheet and test reports so design teams can accelerate selection and verification; the presentation highlights clear specs and datasheet cross‑references for rapid review. (Keyword: MF-RX012)
Point: The part is a polymeric positive temperature coefficient (PTC) resettable fuse in a radial through‑hole package. Evidence: Datasheet mechanical drawings and part‑number suffix notes identify the family as a polymer PTC with radial leads (see datasheet mechanical table). Explanation: This form factor is optimized for low‑voltage board‑level protection where simple through‑hole soldering and straightforward replacement are acceptable; designers should compare the listed specs against rail voltage and expected fault energy before selection.
Point: Multiple current and voltage variants exist within the family, typically indicated by numerical suffixes and packaging codes. Evidence: The datasheet shows variant rows mapping hold/trip currents, voltage ratings and packaging notes (see datasheet table X for variant mapping). Explanation: Create a one‑line mapping from each part number to the datasheet row before procurement so procurement and test teams read the exact specs for the chosen variant.
Point: Designers must verify Ihold (maximum current device will maintain indefinitely) and It / Itrip (current at which the device trips within specified time). Evidence: The datasheet provides Ihold and Itrip per variant and time‑to‑trip ranges (see datasheet table Y). Explanation: Cross‑reference the selected variant’s Ihold/It values with expected operating and inrush currents; use the table below to compactly compare candidate variants against system currents before prototyping.
| Part Variant | Rated Voltage (V) | Ihold (A) | Itrip (A) | Note (datasheet row) |
|---|---|---|---|---|
| Variant A (example) | — (see table) | — (see table) | — (see table) | datasheet table Y, row 1 |
| Variant B (example) | — (see table) | — (see table) | — (see table) | datasheet table Y, row 2 |
Point: Confirm maximum working voltage, initial DC resistance and any post‑trip leakage behavior. Evidence: The datasheet lists maximum working voltage and typical cold resistance per variant (see datasheet electrical table). Explanation: Use rated voltage to determine isolation and placement; compare initial resistance to power‑budget and measure after trip if the datasheet provides post‑trip resistance or leakage limits to ensure downstream circuitry remains safe during a trip event.
Point: Temperature ranges and maximum surface temperature in the tripped state determine placement and clearance. Evidence: The datasheet gives operating/storage limits and maximum temperature rise or surface temperature in a tripped condition (see datasheet thermal table). Explanation: Maintain clearance from heat‑sensitive components and apply derating where ambient or internal heat sources push the device toward its maximum surface temperature during repeated trips.
Point: Soldering profiles, lead heating limits and mounting recommendations affect long‑term reliability. Evidence: Mechanical and soldering notes in the datasheet specify peak lead temperatures and recommended through‑hole soldering practices (see datasheet mechanical notes). Explanation: Follow the datasheet’s soldering cautions; use standoff clearance to mitigate PCB heat soak and to enable consistent trip behavior over the product lifetime.
Point: Time‑current curves illustrate how long the device will hold at a given overcurrent. Evidence: The datasheet provides time‑vs‑current graphs (see datasheet figure Z). Explanation: Annotate the time‑current curve for common fault scenarios—slow overloads (e.g., sustained 1.5× Ihold) versus hard shorts (e.g., >5× Ihold)—to select variants that balance nuisance trips and protection.
Point: Endurance and cycling behavior determine suitable derating. Evidence: The datasheet includes cycle test summaries and recommended derating guidance (see datasheet reliability section). Explanation: If the datasheet shows a decline in performance after repetitive surge cycles, apply conservative derating for continuous or repeated surge environments and plan for periodic verification in long‑life deployments.
Point: The device suits telecom/data‑line and low‑voltage power rail protection. Evidence: Datasheet application notes and typical circuit sketches indicate recommended variants per use case (see datasheet application figure). Explanation: Example 1 — use a lower Ihold variant for data‑line protection to detect small overcurrents; Example 2 — select a higher Ihold variant for 5 V power rails where inrush is expected. These callouts help speed variant choice during schematic design.
Point: Lead spacing, thermal separation and test access affect both trip behavior and verification. Evidence: Mechanical drawing and thermal notes in the datasheet specify recommended clearances (see datasheet mechanical drawing). Explanation: Maintain recommended lead spacing, add a thermal keepout for nearby ICs, and include solder fillet controls; plan bench tests (measured Ihold and time‑to‑trip using controlled current ramps) to validate behavior on the actual PCB.
Point: A concise checklist prevents missed mismatches between part choice and system needs. Evidence: Cross‑reference the electrical, thermal, mechanical and packaging tables in the datasheet (see datasheet table index). Explanation: Verify rated voltage, Ihold/Itrip, time‑current curves, max surface temp, soldering limits and mechanical footprint in order before approving a part for production.
Point: Minimal lab tests confirm lot conformity. Evidence: Datasheet test methods and acceptance criteria summarize expected electrical parameters (see datasheet test section). Explanation: Sample 10 pieces per lot, measure cold DC resistance, perform a controlled ramp to confirm Ihold and time‑to‑trip, and visually inspect for plating/lead integrity; reject if resistance exceeds datasheet tolerance or if trip behavior deviates from specified curves.
Read the curve by locating the x‑axis (time) and y‑axis (current expressed as multiples of Ihold). The datasheet curve shows typical trip times for given overcurrents — designers should match expected fault currents to the curve and allow margin for component tolerances and board thermal conditions.
Critical specs are maximum surface temperature in the tripped state, soldering/lead temperature limits, and mechanical footprint. Use these datasheet fields to set clearances and thermal keepouts so nearby components avoid heat stress during trips.
Measure cold DC resistance, perform hold and trip verification with controlled current ramps, and conduct a visual inspection for lead plating and dimensional tolerances; compare measured values and behavior directly to the datasheet acceptance criteria for pass/fail decisions.
Summary
This report highlights the polymeric resettable fuse’s role in circuit protection and reminds designers to verify three priorities in the datasheet before integration: electrical ratings (Ih/It/voltage), thermal/environmental limits and validated time‑current behavior. (Keyword: MF-RX012; include specs and datasheet references in procurement and test workflows.)