This week’s EYE ON NPI (video) is going to keep you safe and sound, it’s the onsemi portfolio of eFuses – chips that can perform many of the protective functions we build into our power supplies to keep devices from going poof when accidents occur!
onsemi has developed a wide range of eFuses ranging from 3 V to 12 V, supporting a continuous current from 1 A to 12 A. The integrated overcurrent, overtemperature, overvoltage, and inrush current protection, along with the ability to report faults and disable the output through GPIO, make these devices suitable for protecting any system, helping meet the challenges and supporting a compact board layout.
When people first meet fuses, they usually see and think of classic ‘wire’ fuses with ceramic or glass or thermoplastic bodies, and a thin wire inside. When too much current goes through the fuse wire, it gets hotter and hotter and eventually melts, cutting off the load from the source voltage.
- Pros: super cheap, easy to find, lots of suppliers with various current limits
- Cons: only good for overcurrent, one-shot usage only!
Once engineers start making products, they often want to include fuses to protect their circuitry: over-current usually means something is getting damaged and we want to keep away from thermal damage like charring or even a fire. Many traditional/older designs use glass fuses, like appliances, radios, kitchen tools…but a lot of engineers prefer going with ‘poly fuses’ – fuses that are easy to mount into a circuit that auto-reset after a time (usually minutes) so that a temporary overload doesn’t make the device a brick so quickly.
For example, we have a 500mA hold / 1000mA trip polyfuse on the Metro 328 board design. Usually it kicks in when people try to power 4 servos off of the USB port, quickly overwhelming the computer or hub. Poly-fuses are a great step-up from plain wire fuses.
- Pros: also cheap! lots of suppliers with various current limits. auto-resets after cooling down.
- Cons: only good for over-current, can’t latch off, fuse trip time depends on ambient temperature
But circuit protection usually needs more than just over-current checks. We often have to do polarity protection (in case the battery or wall adapter is put in backwards), and over-voltage (to avoid damaging the regulator, which will have some voltage limitation) and under-voltage (to avoid weird or inconsistent behavior during a brown-out). There’s also some products that benefit from ‘latch off’ behavior – where a failure means we have to do a hard power cycle. What if we could do all this in one chip? No surprise, that’s what we’re showing off this week!
The NIS5420 eFuse is a cost effective, resettable fuse which can greatly enhance the reliability of a hard drive or other circuit from both
catastrophic and shutdown failures. It is designed to buffer the load device from excessive input voltage which can damage sensitive circuits. It also includes an overvoltage clamp circuit that limits the output voltage during transients but does not shut the unit down, thereby allowing the load circuit to continue operation.
- Integrated Power Device
- Power Device Thermally Protected
- No External Current Shunt Required
- 8 V to 18 V Input Range
- 39 mOhm Typical
- Internal Charge Pump
- Internal Undervoltage Lockout Circuit
- Internal Overvoltage Clamp
These chips do it all. Obviously they’ve got the current limiting setup, but they also have under-voltage locking, over-voltage clamping for short bursts of high voltage, slew rate control, enable / fault pin, and optional external current monitoring. It’s all analog electronics, so it works instantly, reliably and without digital configuration. Stuff like the current limit and slew rate is set with external passive components. It looks like these were designed for use in hard drives, which means they are good in stressful environments like server racks, data centers or home computers. We always love chips that do something and do it real well, at a good price. These eFuses will replace a chunk of your power-supply protection kit, saving your assembly cost and board size.
While we’re specifically featuring the onsemi NIS5420 here, there’s a whole family of different voltage-set chips to pick from for 3V, 5V, 12V or even 24V power rails. And best of all, they’re in stock right now for immediate shipping from Digi-Key! Order now and you can start designing into your product line tomorrow morning.
See this at Digi-Key at https://www.digikey.com/short/nt2zhct2