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The light in the huge natural cavern was dim, and the room gloomy, reflecting the perpetually dark mood of Dr. Octopus. He grunted and groaned as he tried with his prosthetic arms to prise open a partially damaged laptop computer case, in order to destroy it and make sure it didn’t fall into the wrong hands – especially hands capable of throwing stronger-than-steel webs hundreds of metres in the air at the speed of sound. A few hours before, Dr. Octopus had jabbed the costume-wearing crime fighter in the ribs to fling him across the street, and then sped off with a suitcase containing electronics.
Back in the lair, the laptop eventually came apart, even as the masked crusader watched intently from his perch on the ceiling, waiting for a chance to snatch the device back. The laptop contained many secrets in its 8TB SSD (solid state device or solid-state “drive” – there are no moving parts in it). Dr. Octopus knew the importance of the information within, and had risked everything to destroy it, inadvertently giving his worst nemesis a chance to follow him to his protected hideout. To make sure the contents of the SSD were truly and permanently destroyed, the Master Planner smashed its case and then for good measure used an electromechanical arm to release a strong bolt of electricity at its ports, grinning as it visibly crackled and popped and turned blue for a few moments.
What he didn’t count on, was that SSDs and hard-disk drives (HDDs) in applications ranging from PCs to data-centers contain eFuses from ON Semiconductor. These eFuses protect appliances by ‘fusing’ (going into OPEN circuit) when over-current conditions are encountered, and in this way are similar to regular fuses. The difference is that these devices can be electronically reset into the conducting state. eFuses offer several additional features whose specs are continually improving: our latest eFuses include integrated features such as a charge pump, sophisticated overcurrent protection, thermal shutdown, a tristate enable pin, undervoltage lockout and overvoltage protection with output voltage clamping.
Not all eFuses are the same. In today's power systems, efficiency is critical, and lower-performing eFuses can actually have a deleterious impact on overall system performance. The critical parameter is RDS(ON), which is the static-state resistance of the eFuse as determined by the internal MOSFET. Low values of RDS(ON) ensure that power transfer during normal operation is efficient and very little power is wasted. More efficient operation also allows for operation at higher ambient temperatures with a relatively small temperature rise in the device, meaning that less cooling is needed, which can translate to space savings. Although eFuses can operate up to 150˚C, the lower the operating temperature, the better its life expectancy. This is especially important, as data-center hardware is expected to be long-lived with an operating lifetime that is 10 years or longer.
The latest eFuses from ON Semiconductor (NIS5431 and NIS5452) have a typical RDS(ON) of just 33mΩ, which is less than half that of the earlier generation’s NIS5135. As in Fig. 1, the newer devices include an integrated high-side n-channel power MOSFET with a gate voltage that is boosted by a charge pump.
Figure 1. Integrated high-side n-channel power MOSFET with a gate voltage.
After Dr. Octopus dispatched the battered laptop and SSD off the cliffside into the raging waters below, a bruised and bleeding Spidey slinked out of the damp cave and crouched on the edge to peer over it, before shimmying down the rock-face at an impossible angle. It was almost six hours before he retrieved the electronics and delivered them to the Data-Medic lab for analysis. Sure enough, the eFuses had protected the SSD from the harmful electrical zap, and it was just a matter of time before Flash chips were extracted from the device and mounted into a new case, providing access to a wealth of data including a prime number with 12,837,064 digits that was used to encode names of evil-doers, their locations and incriminating data about their exploits world-wide.
Should more than the rated current of 5A be required, eFuses can be used in parallel by simply connecting the enable pins, inputs and outputs together. Equal current sharing is automatic, due to the positive temperature coefficient of RDS(ON). An evaluation board to demonstrate this is shown in Figs. 2 and 3.
Fig 2. Evaluation board showing four NIS5452’s configured in parallel.
Figure 3. Four NIS5452 devices running in parallel conducting a total of 20 A and a max. case temperature of 56 degrees C.
Internally a highly efficient SenseFET architecture allows for current limiting to protect against fault conditions. This arrangement offers significant power savings over a sense resistor and is conveniently programmed by an external resistor, RLIMIT. An adjustable slew rate feature controls inrush current when providing power to highly capacitive loads.
The latest NIS5452 and NIS5431 can be tested on a NIS5452MT1GEVB standard evaluation board that features several components to simplify testing. Click here for more info or contact your local sales representative for evaluation boards and samples and any other help you need in your crime-fighting efforts!
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