The **FSMD010-0603-R** is a Surface Mount Device (SMD) **Polymeric Positive Temperature Coefficient (PPTC)** resettable fuse. It is commonly used for overcurrent protection in compact electronic circuits. --- ### 1. Technical Specifications The part number follows a specific nomenclature that defines its physical size and electrical characteristics. | Parameter | Value / Description | | :--- | :--- | | **Part Number** | FSMD010-0603-R | | **Package Size** | 0603 (Metric 1608) | | **Hold Current ($I_{hold}$)** | 0.10 Amps (100mA) | | **Trip Current ($I_{trip}$)** | 0.30 Amps (300mA) | | **Max Voltage ($V_{max}$)** | 15V | | **Max Current ($I_{max}$)** | 40A | | **Typical Power ($P_d$)** | 0.5W | | **Operating Temp** | -40°C to +85°C | --- ### 2. How it Works (The PPTC Principle) Unlike a standard one-time fuse that melts and breaks the circuit permanently, the FSMD010 is "resettable." 1. **Normal State:** The device has low resistance, allowing current to flow to the load. 2. **Fault State (Overcurrent):** When current exceeds the trip threshold ($I_{trip}$), internal $I^2R$ heating causes the polymer matrix to expand. 3. **Tripped State:** The expansion breaks the conductive carbon chains, increasing resistance exponentially. This limits the current to a safe leakage level. 4. **Reset:** Once the fault is removed and the power is cycled or the device cools down, the polymer shrinks, the carbon chains reconnect, and the fuse returns to a low-resistance state. --- ### 3. Key Features * **Form Factor:** The 0603 footprint (1.6mm x 0.8mm) is extremely small, making it ideal for high-density PCBs. * **RoHS Compliant:** The "-R" suffix typically denotes compliance with RoHS environmental standards (Lead-free). * **Automated Assembly:** Compatible with high-speed SMT (Surface Mount Technology) pick-and-place machines. --- ### 4. Common Applications Due to its small size and 100mA hold current, this component is frequently found in: * **USB Port Protection:** Protecting against shorts in peripherals. * **Battery Packs:** Overcurrent protection for Li-ion cells. * **Consumer Electronics:** Smartphones, tablets, and wearables. * **HDMI/DisplayPort:** Protecting low-voltage signal lines. ---