Protection
Chip Fuses
One-shot over-current protection for fault containment.
What is it?
A chip fuse is a small SMD device with a metal element that melts and breaks the circuit when current exceeds its rating for long enough. Unlike a resettable PTC, a chip fuse is single-use, once blown, replace it. Chip fuses respond much faster than PTCs at high over-currents, making them the right choice for short-circuit fault containment.
When do you need it?
- DC rails within the fuse rating, such as DDR5 module inputs, USB and peripheral power, and 12-48 V I/O (Magnias chip fuses are rated 24 V to 72 V DC, depending on series and current).
- Battery-pack output where short-circuit current can be very high.
- Critical-fault containment where you specifically WANT the device to be removed from service after a fault (so a technician investigates).
- PCB-level over-current protection for cost-sensitive designs.
How to pick the right one
- Rated current (In)
- The maximum continuous current. Pick at least 25% above your worst-case normal current.
- Breaking capacity (IR)
- Maximum short-circuit current the fuse can interrupt safely. Critical for high-voltage rails.
- Rated voltage (UR)
- Maximum DC or AC voltage the fuse can clear after melting.
- Response type (FF / F / T)
- Very-fast (FF) for semiconductor protection, fast (F) general, slow / time-lag (T) for inrush tolerance.
- Package
- 0402, 0603, 1206, 1210, 2410, bigger = more current rating.
What Magnias offers
Magnias chip fuses are available in 0402, 0603 and 1206 SMD packages, rated 250 mA to 40 A, all fast-acting. Halogen-free and RoHS compliant. DDR5 module fuses: MGF06F-6000A (6 A, RDIMM raw card rev 0 / rev 1), MGF06F-7000A (7 A, RDIMM rev 2) and MGF04F-2000A (2 A, 0402, DDR5 CAMM2).
Common questions
Fuse or resettable PTC?
A chip fuse is the simple, low-cost way to contain a hard fault: it opens once and stays open. A resettable PTC recovers after the fault but trips more slowly and has higher resistance. Some designs use both: a PTC for routine overloads, a fuse for catastrophic faults.
How fast does a fuse blow?
Depends on the fuse type and the over-current ratio. A fast 1 A fuse at 5 A might blow in <10 ms; at 1.5 A it could take 10+ seconds. Always check the I²t curve in the datasheet.
Can fuses fail intermittently?
Yes, fatigue from repeated near-rating cycles can weaken the element. Don't run fuses at >75% of rating continuously.