Because electronic systems have become more interdependent, it is important to quickly isolate overcurrent faults to block potential damage to adjacent systems or circuits. Similarly, ambient temperature nuisance tripping, inrush current or other events that present no risk to the system should be minimized to ensure that the integrated system remains online. The latest connected applications can be particularly vulnerable to overcurrent events that can cause the failure of one or more devices, which seriously effects the reliability of the network.
Dependable circuit protection solutions are now critical to maintain reliability for these highly integrated and interdependent applications especially if they need to operate in severe environments. A case in point are the integrated electronics in automotive systems that typically are subjected to wide temperature variations. Vehicle applications also have strict reliability standards that designers need to adhere to including engine controls, battery management systems (BMS) and comfort/convenience features where overcurrent protection solutions are required to help meet these requirements.
Protecting Against Overcurrent Threats
A major consideration influencing hybrid and electric vehicle market growth is the rise in the quantity of electronic components designed in to support enhanced performance and comfort features. This increasing number of components is in direct relation to the increase in the number of potential fault conditions these applications may experience. Correspondingly, this expansion in possible fault conditions has prompted designers of emerging high energy systems to look for circuit protection components that are able to protect multiple elements of the design. For instance, overcurrent protection is necessary in a BMS design for the main control power input, slave control monitor lines and cell balance lines as well as in the battery module and connection board.
Fuses are an excellent solution to protect against overcurrent threats caused by a transitory fault condition that can lead to severe circuit or system damage. As consumer demands call for smaller and smaller embedded electronics while adding more features, there is also a growing demand for space-saving surface mount (SMD) fuses that can be easily mounted to a PCB. Also helping automotive system designers is that advanced AEC-Q200 equivalent compliant fuses are now available. These compliant fuses provide the higher reliability that is needed for operation in certain harsh environmental conditions.
Heightened Automotive Grade Fuse Criteria
Designating a component as “automotive grade” can vary widely by manufacturer. Generally, automotive grade components feature the use of superior raw materials along with a robust design, tight production control and strict quality compliance. These features can make a difference for reliable operation in certain harsh environments. That’s why Bourns has a number of heightened criteria it sets for its automotive grade fuses. First, Bourns automotive grade fuses are manufactured fully certified to IATF 16949 facilities. They are also tested and qualified according to an AEC-Q200 equivalent product validation standard for passive components. These measures have been put in place to help ensure that any new Bourns automotive grade product or new process development meets or exceeds the requirements established in the latest AIAG revision of the Advanced Product Quality Planning (APQP) process.
Cutting-Edge Fuse Design
To reliably withstand a surge within the device’s rated specifications, the construction of an SMD fuse is important. An effective approach that Bourns uses is in its innovative PCB wire core design. Bourns’ design methodology for its SinglFuse products delivers enhanced voltage and current handling capabilities and more precise hot spot control along the fuse element than alternative designs in similar package sizes. The SMD fuse design also provides improved arcing suppression and inrush current withstand capability, and superior structural integrity when blown compared to typical legacy ceramic tube fuse designs. These precision fusing characteristics support a wide range of voltage, current and breaking capacity ratings, thus allowing designers to effectively meet a variety of application-specific overcurrent protection requirements.
In addition, Bourns has developed a cutting-edge multilayer ceramic design that makes even greater voltage and current handling capabilities possible. Bourns’ SinglFuse SMD line includes models in small 1206 and 0603 package sizes that feature high inrush current withstand capabilities and time-lag fusing speeds.
Auto Grade Fuse Selection Considerations
It is a regular occurrence in certain automotive applications to experience start-up pulses. That is why automotive designers frequently specify fuses based on their inrush current withstand requirements. Fuses with boosted inrush handling capabilities, allow the application to operate reliably in inrush conditions. Fuses with boosted inrush capabilities also are susceptible to nuisance tripping and still offer the necessary protection against unwanted sustained overcurrent conditions. It is also a good rule of thumb for designers to determine the expected duration of a condition when specifying the fuse type.
Other important automotive grade fuse selection considerations are current and voltage ratings and fusing speed. Bourns’ industry-leading automotive grade SMD fuse portfolio offers rated currents from 0.5 A to 20 A, with a wide range of rated voltages from 24 V to 250 V and available package sizes that range from EIA 2410 down to 0603.
When choosing a fuse based on fusing speed requirements, it is recommended to look for a supplier that has multiple fuse type options. For instance, Bourns offers fast-acting, slow blow and high inrush withstand fuse types.
Some helpful reminders are that fast-acting fuses react quickly to an overcurrent condition compared to a slow blow fuse that will endure short-duration spikes such as those that tend to occur during the initial power up of electronics. Slow blow fuses are designed to trip only when the spike is presented long enough to be a continual overload or short circuit. Specifying a slow blow fuse in place of a fast-acting fuse needs to be carefully evaluated since it may not open quickly enough to protect sensitive electronics from an overcurrent event.
Applications for Automotive Grade SMD Fuses
With their advanced features, various voltage, current ratings and fusing speeds, rugged construction and wide temperature range operation, Bourns’ automotive grade SMD fuses are capable of meeting specific protection requirements. In an on-board charger (OBC) application, an SMD fuse can be used as primary overcurrent protection between the power grid and the DC-DC converter. Or, for USB I/O port protection, fuses with optimized voltage and current ratings are ideal for systems that utilize DC/DC converters, such as 48 V – 12 V. In a BMS design, SMD fuses can be utilized as both primary overcurrent protection on the BMS controller board and for battery cell overcurrent protection.
The protection and space-saving advantages of automotive grade SMD fuses can go beyond vehicle applications. Bourns’ high-reliability overcurrent protection solutions are also ideal for telecom and networking infrastructure equipment, cloud computing and storage systems, high-end consumer electronics and smart appliances, and industrial IoT and robotics.
Also ideal for rugged application needs is Bourns’ line of High Temperature Surface Mount Polymer Positive Temperature Coefficient (PPTC) resettable fuses. Its expanding PPTC roadmap includes a broader standard high temperature offering that meets increasing working temperature and power rating requirements with products that feature greater resettable fuse performance in a smaller footprint.
Automotive-grade SinglFuse Product Training Module: https://www.bourns.com/resources/training/circuit-protection/singlfuse-smd-fuses/singlfuse-aec-q200-equivalent-compliant-smd-fuse-training-module
Automotive-grade SinglFuse Product Page: https://www.bourns.com/products/circuit-protection/singlfuse-smd-fuses-aec-q200-compliant
Automotive-grade Multifuse Product page: https://www.bourns.com/products/circuit-protection/resettable-fuses-multifuse-pptc-aec-q200-compliant
Article by: By Shawn Yu, Fuse Product Manager at Bourns (OEM&Supplier by VEK Publishing, Issue 1/2022)
