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IEC62281 Datasheet(PDF) 4 Page - Littelfuse |
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IEC62281 Datasheet(HTML) 4 Page - Littelfuse |
4 / 8 page 4 c n I , e s u fl e tt i L 12 0 2 © Application Note: Use of Low Resistivity Surface Mount PPTC in Li-ion Polymer Battery Packs General Safety Standard that Applies to Smartphones and Tablets IEC/UL/EN 60950-1 - Information Technology Equip- ment Safety, Part 1: General Requirement ● The standard applies to battery operated devices that can be charged from AC mains supply. ● Sec 2.5 – Limited Power Source – Fire enclosure requirements in 4.7.2 are reduced or not required if the components/connectors are connected to a Limited Power Source. – This allows designer to reduce cost, use thinner materials, etc. – Limited Power Source spec has two tables: ● Table 2B – no OC protective device (so using PTC or electronic fuse) – Must limit current to 8A within 5 sec if using PTC ● Table 2C – OC protective device is used (fuse) – Fuse rating 5A or less (210% / 120sec overload gate) – Limit Short ckt current to less than 1000 / Vmax and 250VA within 60sec ● Where an overcurrent protective device is used, it shall be a fuse or a non-adjustable, non-autorest, electromechanical device Agency Approvals: Littelfuse PPTCs are recognized under the Component Program of Underwriters Laboratories to UL Standard 1434 for Thermistors. The devices have also been certied under the CSA Com- ponent Acceptance Program. Introduction to PPTC Technology PTC stands for Positive Temperature Coefcient, which means the resistance of the device increases as its temperature goes up. PTCs increase in resistance as temperature increases due to increased current ow. Polymer PPTC (PPTC) devices are made of a polymer plastic material. Unlike a typical “one-time” fuse, a PPTC device (see Figure 4) will reset when cooled. Figure 4. How a PPTC works Figure 5. PPTC resistors Carbon Crystalline Polymer Under Normal Operation ■ At operating current ■ Many conductive paths ■ Very low resistance Carbon Amorphous Under Fault Condition ■ Excessive current causes device to heat up ■ Fewer conductive paths ■ Result is high resistance ■ Cools down and resets when fault is removed How a PPTC Works RPTC RL I V Voltage Source Load Resistance |
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