The **FSMD020-1206-R** is a Surface Mount Device (SMD) Resettable PTC (Positive Temperature Coefficient) fuse, commonly known as a **PolySwitch**. It is designed to provide overcurrent protection for electronic circuits. --- ### 1. Technical Specifications Below are the primary electrical and physical characteristics of the FSMD020-1206-R: | Feature | Specification | | :--- | :--- | | **Package / Case** | 1206 (3216 Metric) | | **Hold Current ($I_{hold}$)** | 0.20 A (200 mA) | | **Trip Current ($I_{trip}$)** | 0.42 A (420 mA) | | **Max Voltage ($V_{max}$)** | 30V | | **Max Current ($I_{max}$)** | 100A | | **Typical Power ($P_d$)** | 0.6 W | | **Resistance (Min/Max)** | $0.650 \Omega$ to $3.500 \Omega$ | --- ### 2. How it Works The FSMD020-1206-R functions as a "resettable" fuse through the following cycle: 1. **Normal State:** The device has very low resistance, allowing normal current to flow to the circuit. 2. **Fault State (Overcurrent):** If the current exceeds the trip threshold ($I_{trip}$), the internal polymer heats up rapidly. 3. **Tripped State:** The heat causes the polymer to expand into an amorphous state, increasing the resistance exponentially. This limits the current to a safe leakage level. 4. **Reset State:** Once the power is removed and the fault is cleared, the device cools down, the polymer shrinks, and the resistance returns to a low value. --- ### 3. Key Components & Material * **Conductive Polymer:** The core is made of a non-conductive polymer mixed with carbon black particles. * **Terminations:** Solderable nickel/gold or tin plating for surface mount assembly. * **Standard Compliance:** RoHS compliant, Lead-free, and usually Halogen-free. --- ### 4. Common Applications Due to its small 1206 footprint and 200mA hold current, this part is ideal for: * **USB Port Protection:** Safeguarding peripherals against shorts. * **Battery Packs:** Protecting cells from over-discharge or short circuits. * **Motherboards:** Protecting signal lines and I/O ports. * **LED Drivers:** Preventing thermal runaway in lighting circuits. ---