Hi all,
I am going to use this fuse on my board: https://www.mouser.co.uk/ProductDetail/Littelfuse/AHS080-2018-2?qs=fvkeCqCHl3AybvLOzBRZnw%3D%3D
What footprint can I use for this in Kicad V4?
Many thanks,
Andy
The manufacturer tells you that this component’s package is a variant of the standard SMD " 2018 " (" 5050 Metric ") package style. KiCAD’s footprints for passive components (resistors, capacitors, inductors, LED’s, etc) don’t seem to include that package size.
I would go to one of the libraries for SMD passives (e.g., “Capacitor_SMD.pretty”, “Resistor_SMD.pretty”, etc) and select a footprint that is close to the size you need, such as “C_2010_5025Metric.kicad_mod”, or “R_2010_5025Metric_Pad1.34x2.70mm_HandSolder.kicad_mod”. Load the footprint into the footprint editor, and modify it to fit the PPTC fuse. The manufacturer suggests some footprint dimensions on page 27 of their Data Sheet. Alter the footprint to fit your specific situation - extended pads for manual soldering, and increased courtyard to keep it away from heat-producing components, are potential modifications that come to mind. Then save the footprint, with a different file name, in your personal library.
Dale
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Is there a better choice of PPTC fuse available that you know of - that fits a more standard size which would save me this work?
Or use the generator that is used to generate all these footprints in the official lib. https://github.com/pointhi/kicad-footprint-generator/tree/master/scripts/SMD_chip_package_rlc-etc
Usage: ‘python3 SMD_chip_package_rlc-etc.py SMD_chip_devices.yaml’ (enter your devices size to the fuse.yaml file)
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I would rather just have a 1206 or more standard sized fuse. Can you help me locate one?
It needs to handle 800mA at 3.3v as a hold current.
Do you think this would do : https://www.mouser.co.uk/ProductDetail/Littelfuse/1206L075THYR?qs=sGAEpiMZZMsxR%2BBXi4wRUMH1rxFWZCBF4B90EjaVadw%3D
0.750mA should be ample, and I think thats a 1206.
It would be helpful for the datasheet to advise on track connection, not just the pad. The heatsinking of a wide track will have an effect on the trip current
A Thru-hole fuse (if you have the room for it) is better, for reasons related to what David observes above.
My experience with these fuses (both TH and SMD) is a bit mixed. They do save you from grief but once blown, and cooled down to reset state, they will exhibit non-trivial resistance… so be prepared to see the IR drop of several hundred mV etc after it resets (depending on your circuit). Good to have in your first prototypes though. Once you are sure you have protection elesewhere, just replace them with 0-Rs (handy to isolate power lines for troubleshooting).
They do take a while to “heal” after cooling to their default dc resistance. The datasheet specifies the resistance one hour after tripping.
Normal fuses also have some temperature dependence and a spread on fusing current. A good quality 1A 20mm fuse at 25C might blow with as little as 1.5A or need as much as 2.2A dc to fail. Buy something from auction sites and who knows.
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