The **FSMD030-2920-R** is a surface-mount Resettable Positive Temperature Coefficient (PTC) device, commonly known as a **Resettable Fuse** or **Polyfuse**. It is designed to protect electronic circuits from overcurrent and short-circuit conditions. ### 1. Key Technical Specifications The part number itself contains information regarding its form factor and electrical ratings. | Parameter | Specification | Description | | :--- | :--- | :--- | | **Hold Current ($I_{hold}$)** | 0.30 A (300mA) | Maximum current the device can carry without tripping. | | **Trip Current ($I_{trip}$)** | 0.60 A (600mA) | Minimum current at which the device will switch to high resistance. | | **Max Voltage ($V_{max}$)** | 60V | Maximum voltage the device can withstand safely. | | **Max Current ($I_{max}$)** | 100A | Maximum fault current the device can interrupt. | | **Package Size** | 2920 (EIA) | Physical dimensions: 7.5 x 5.0 mm (0.29 x 0.20 inches). | | **RoHS Status** | Compliant (-R) | Lead-free and environmentally friendly. | --- ### 2. How it Works The FSMD030-2920-R operates on the principle of thermal expansion: 1. **Normal Operation:** Under normal current levels, the conductive particles inside the polymer form a low-resistance path. 2. **Fault Condition:** When an overcurrent occurs, the internal temperature rises due to $I^2R$ heating. This causes the polymer to expand, breaking the conductive paths. 3. **Tripped State:** The device jumps to a high-resistance state, limiting the current to a safe leakage level. 4. **Resetting:** Once the power is removed or the fault is cleared, the device cools down, the polymer contracts, and the conductive paths are restored. --- ### 3. Application Use Cases This specific component is widely used in power management for sensitive electronics: * **USB Port Protection:** Protecting ports from short circuits or drawing too much power. * **Battery Packs:** Preventing damage during charging or discharging cycles. * **Industrial Controls:** Safeguarding PLC inputs and outputs. * **Power over Ethernet (PoE):** Providing protection for networked hardware. --- ### 4. Comparison: PTC Fuse vs. Standard Fuse | Feature | FSMD030-2920-R (PTC) | Standard Wire Fuse | | :--- | :--- | :--- | | **Action** | Resettable | One-time use (Blows) | | **Maintenance** | None required | Must be physically replaced | | **Resistance** | Slightly higher | Very low | | **Tripping Speed** | Slower (Thermal-based) | Faster (Melting-based) | ---