The **FSMD250-2920-R** is a Surface Mount Device (SMD) **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse. It is commonly used in electronic circuits to provide overcurrent protection without the need for manual replacement after a fault. --- ## 1. Technical Specifications The following table outlines the key electrical and physical parameters for this specific component: | Parameter | Specification | | :--- | :--- | | **Part Number** | FSMD250-2920-R | | **Package Type** | 2920 (Metric 7550) | | **Hold Current ($I_{hold}$)** | 2.50 Amperes | | **Trip Current ($I_{trip}$)** | 5.00 Amperes | | **Max Voltage ($V_{max}$)** | 15 Volts | | **Max Current ($I_{max}$)** | 100 Amperes | | **Typical Power ($P_d$)** | 1.50 Watts | | **Operating Temperature** | -40°C to +85°C | --- ## 2. Operating Principle Unlike a standard fuse that melts and creates an air gap (breaking the circuit permanently), the PPTC operates as follows: 1. **Normal State:** The conductive polymer is in a crystalline state, allowing electrons to flow easily (low resistance). 2. **Fault State (Overcurrent):** When current exceeds the trip threshold, $I^2R$ heating causes the polymer to expand and become amorphous. 3. **High Resistance:** This expansion breaks the conductive paths, increasing resistance significantly and dropping the current to a safe leakage level. 4. **Reset:** Once the fault is removed and the device cools down, the polymer contracts, and the conductive paths are restored. --- ## 3. Key Features and Applications ### Features * **Surface Mount Design:** Optimized for automated PCB assembly. * **Resettable:** Reduces maintenance costs and improves product uptime. * **Fast Response:** Quickly reacts to fault currents to protect sensitive downstream components. * **RoHS Compliant:** Lead-free and environmentally friendly. ### Common Applications * **Computer Peripherals:** USB ports, IEEE 1394 (Firewire) protection. * **Battery Packs:** Protecting Li-ion cells from short circuits. * **Telecommunications:** Protection for line cards and networking equipment. * **Industrial Controls:** Low-voltage power supply protection. --- ## 4. Soldering Profile (Reflow) Because this is an SMD part, it must be soldered using standard reflow profiles. Excessive heat duration can permanently damage the polymer structure. ```markdown Recommended Reflow Settings: - Preheat Temp: 150°C to 200°C - Peak Temperature: 260°C (Max) - Time above 217°C: 60 - 150 seconds ```