The **FSMD260-2920-R** is a surface-mount (SMD) **Polymeric Positive Temperature Coefficient (PPTC)** device, commonly referred to as a **Resettable Fuse**. It is manufactured by **Formosa Microsemi** and is designed to protect electronic circuits from overcurrent and over-temperature conditions. --- ### 1. Key Technical Specifications The following table outlines the primary electrical characteristics of the FSMD260-2920-R: | Parameter | Specification | Description | |:---|:---|:---| | **Hold Current ($I_{hold}$)** | 2.60 A | Max current the device will pass without tripping. | | **Trip Current ($I_{trip}$)** | 5.20 A | Min current at which the device will switch to high resistance. | | **Rated Voltage ($V_{max}$)** | 6.0 V | Maximum voltage the device can withstand without damage. | | **Max Current ($I_{max}$)** | 100 A | Maximum fault current the device can safely interrupt. | | **Package Size** | 2920 (7555 Metric) | Dimensions: approx. 7.5mm x 5.5mm. | | **Resistance ($R_{min}/R1_{max}$)** | 0.015 - 0.050 $\Omega$ | Initial resistance and post-trip resistance range. | --- ### 2. How it Functions (PPTC Principle) The FSMD260-2920-R operates based on the thermal properties of a conductive polymer: 1. **Normal State:** Under normal operating currents, the polymer is in a crystalline state with conductive carbon particles forming a low-resistance path. 2. **Tripped State:** When an overcurrent occurs, $I^2R$ heating causes the polymer temperature to rise. Once it hits a threshold, the polymer expands into an amorphous state, breaking the carbon chains. The resistance increases dramatically, limiting the current to a safe leakage level. 3. **Reset:** Once the fault is removed and the power is cycled or the device cools down, the polymer shrinks, re-establishing the conductive paths. --- ### 3. Application Use Cases This specific part is often found in high-current, low-voltage environments: * **USB Ports:** Protection for USB 2.0/3.0 ports and hubs. * **Battery Packs:** Protection against short circuits in Li-ion or NiMH battery charging circuits. * **Motherboards:** Protecting sensitive traces on computer peripherals. * **Power Supplies:** Secondary protection for DC-DC converters. --- ### 4. Code Implementation Example (Monitoring) While a fuse is a passive component, in high-reliability systems, you might monitor the voltage drop across it using an ADC to detect a "Tripped" state: ```python # Simple Logic for Trip Detection def check_fuse_status(adc_voltage_drop, current_draw): # Resistance of FSMD260 is approx 0.02 Ohms expected_drop = current_draw * 0.02 if adc_voltage_drop > (expected_drop * 10): return "TRIPPED: High Resistance Detected" else: return "NORMAL" ``` ---