Consumer Electronics TFF Training Training Agenda – Thin Film Fuse (TFF) Definition and Circuit Protection – TFF Basic Characteristics and Related Physics – Typical TFF Application Examples – TFF Selection Concepts – Littelfuse TFF Brands and Future Development – Frontiers of TFF Technology Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 1 Consumer Electronics TFF Training Section 1 TFF Definition and Circuit Protection TFF Definition – In an electrical circuit, a Thin Film Fuse (TFF) is a calibrated, intentionally weak fuse-link that provides overcurrent protection. TFF Circuit Protection Concepts – Potential safety threats that require circuit protection • Protect abnormal operation of a circuit caused by component failure – Regulatory requirements related to circuit protection • IEC/UL requirements where faults are expected to occur frequently and changing fuses or resetting breakers is undesirable Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 2 TFF Definition and Consumer Electronics Circuit Protection TFF Definition – In an electrical circuit, a Thin Film Fuse (TFF) is a calibrated, intentionally weak fuse-link that provides overcurrent protection, protecting sensitive electrical circuitry against damaging overload and short circuit conditions. – The Thin Film Fuse element is a patented bimetal design. The fusing mechanism is a thermally driven event. When current is carried by the element, the element undergoes Joule Heating (l2R). During an over current condition the elements heats up to a point where its capability to carry current diminishes and the element melts, vaporizes and the conduction path is opened. – A TFF fuse in the circuit will operate before a catastrophic event occurs and prevent a fire. Electrical components such as ICs, capacitors, transformers, resistors, etc. can fail due to manufacturing defects, old age, or extreme environmental conditions (aging), and if this happens, the circuit could draw an excessive amount of current and possibly catch fire. – A TFF Fuse does not prevent a fault occurring, but will operate quickly to prevent further damage from occurring or the equipment from becoming a safety hazard. The fuse will also limit the extent of the damage to a small part of the equipment making repairs less costly. Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 3 TFF Definition and Consumer Electronics Circuit Protection Circuit Protection Needs in Consumer TFF Segment – Secondary protection of electrical circuits particularly those in consumer and general electronic systems such as laptops, mobile phones, PDAs, MP3 players, digital cameras, hard disc drives, modem cards, LCD inverters – Terminals that might get grounded or shorted • Cell phone batteries, DC power ports – Process controllers and monitors – Load and power management ICs Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 4 Consumer Electronics TFF Training Section 2 TFF Characteristics and Device Physics Basic TFF Characteristics – Current rating – Voltage rating – Temperature rating – Time-current characteristic – Interrupt rating TFF Construction and how it affects the related TFF characteristics – TFF Element vs. electrical characteristics – TFF Package vs. maximum ratings – TFF De-rating Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 5 TFF Characteristics and Device Physics TFF Electrical Characteristics – TC Curve • Defines the fuse opening time • Directly denotes the fuse rating – Slo-Blo vs Fast Acting The structure of the fuse element determines the fuse opening characteristics. Generally, the fast acting fuse has the straight fusing element while the Slo Blo TFF fuse has a serpentine shape fusing element. Fast Acting Slo-Blo Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 6 TFF Characteristics and Device Physics TFF Electrical Characteristics Thin Film Fuses react to overloads or short circuit conditions by melting or vaporizing the fusing element. Usually the overload condition should be more than 150% of the rated current. The opening time is determined by measuring the melting time of the TFF with a constant current power source. A current shunt is used in the current measurement for accurate opening time of the TTF fuse. SMD TFF Test Scheme Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 7 TFF Characteristics and Device Physics TFF Electrical Characteristics Thin Film Fuses function by reacting to the heat generated due to excessive current flow. Once the fuses I2t rating is exceeded, the center conductor opens. Exceeding the fuses I2t is an Adiabatic process: no heat is transferred to the surroundings. All energy is concentrated into a specific area for a split second. The I2t is a measure of the energy required to open the fuse when subjected to an adiabatic current pulse. Due to [adiabatic] current pulses the fusing element is stressed (thermally and mechanically). Depending on the energy and number of pulses it will suffer from aging from fatigue, pre-diffusion and oxidation. Fuse opening time measurement Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 8 TFF Characteristics and Device Physics TFF Fuse Construction There are mainly four components of the TFF fuse construction: The substrate, fusing element, protective polymeric coating, and termination. Terminations The substrate is made of high performance glass / polymer, the fuse element is formed by Cu/Sn, and the termination is by Cu/Ni/Sn. The available footprint of the TFF fuses are as following: 1206 Fast Acting 1206 Slo Blo 0603 Fast Acting 0402 Fast Acting Lead-Free & RoHS compliant TFF series are available. Substrate Fusing Element Polymeric Coating The TFF is UL recognized and CSA certified. Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 9 Consumer Electronics TFF Training Section 3 TFF Consumer Electronics Applications Examples Personal Computers (PCs) And Peripherals PC Cards Printers Network Interfaces Battery Protection Portable Devices (Cell Phones, Laptops, PDAs, & Palm Computers) Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 10 TFF Consumer Electronics Applications Examples Portable Device DC/Power Line Protection For portable devices, the power bus of the battery pack should be protected against an overcurrent runaway condition of the Li-ion cell. A TFF should be used for short circuit and over current protection. Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 11 TFF Consumer Electronics Applications Examples DC Power Secondary Protection For products that include an external AC adapter, a DC voltage (typically in the range of 5VDC to 18VDC) will be supplied. As shown above, a TFF can be used for short circuit and overload current conditions. Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 12 TFF Consumer Electronics Applications Examples Battery System Protection There are many instances where a short circuit condition could happen to a battery. Also, a battery could exposed to a high temperature during normal operation. A TFF can be used to protect battery from explosion due and extreme overtemp causing a runaway thermal condition and unacceptably high discharge rate. Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 13 TFF Consumer Electronics Applications Examples Global Lab Capabilities • • • • Qualification of all LF products UL-Approved Customer Testing in ISO 17025 Lab (Des Plaines) – High power (AC/DC up to 1KV/50KA) UL approvals available in DP – Telcordia approvals in DP planned (2008) Verification of Telcordia, ITU, IEC, FCC, and other industry, regulatory, and safety standards – Verification to various OC and OV standards • Insure application meets standards before submitting for approval Customer Application testing – Assistance with design-in and performance verification • Help with selection of appropriate technology and rating – Application troubleshooting • Assistance insuring proper OV/OC and primary/secondary protection coordination – Competitive evaluations • Competitive or technology performance comparisons – Reliability & Tin Whisker data/testing Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 14 Consumer Electronics TFF Training Section 4 TFF Consumer Electronics Application Product Selection Identify normal operating current of circuit to be protected Identify ambient working temperature to which the fuse will be exposed Estimate magnitude of the In-rush current, peak, pulse shape, duration, and number of pulses Select maximum operating voltage Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 15 TFF Consumer Electronics Applications Product Selection TFF Rating Selection and TC Curve — — — — Time Current (TC) Curves present the average values of the trip time at a given current for every part number. TFF opening times will be distributed above and below the curve. Lower percentage overloads result in a greater variation in opening time. Verification testing needs to be done for actual application. Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 16 TFF Consumer Electronics Applications Product Selection TFF De-Rating Curve Resistance of the TFF device changes directly with temperature. The rating of the TFF is influenced by the ambient temperature as shown at the temperature de-rating chart for the A line. The heat required to open the device may come from several sources. Some common sources are: — resistive heating from the electrical current — ambient environment — adjacent components Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 17 TFF Consumer Electronics Applications Product Selection Some TFF Board Application Guide Lines The I2t must be considered for the selection of the TTF fuse to compare with the pulsing I2t of the signal. The fuse voltage rating is the maximum allowable applied voltage at which the fuse can open safely (arcing occurs when the fuse element melts, the voltage rating defines the maximum suppressible arc). Standard voltage ratings are 16, 32, and 63V DC. Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 18 Consumer Electronics TFF Training Section 5 Littelfuse TFF Product Road Map – TFF Road Map – New 0402 Ratings – Higher Operating Temperature 1206 TFF Fuses (Rated to 135C) – Higher Operating Temperature 0603 TFF Fuses (Rated to 135C) – New 0201 Very Fast-Acting Fuse – Smallest Ever Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 19 Consumer Electronics TFF Training Section 6 Consumer Electronics TFF Technology Challenges – Multi Elements in Single Package – TFF Technology Combined with other Technologies in a Single Package – Improved De-rating Characteristics – Higher Operating Temperatures – Hi-Rel TFF Development Confidential and Proprietary to Littelfuse, Inc. © 2007 Littelfuse, Inc. All rights reserved. 20