Resettable over-temperature protection devices protect batteries

Smaller, safer battery-powered devices with longer battery life can be created using the MHP-TAC series resettable over-temperature protection devices from Littelfuse.

The MHP–TAC (metal hybrid PPTC – thermal activated compact) series resettable over-temperature protection devices are the latest addition to Littelfuse’s line of battery min-breakers.

The devices connect a PPTC (polymeric positive temperature co-efficient) device in parallel with a bi-metal protector (a resettable thermal cut-off device) to protect the high-capacity lithium-ion polymer (LiP) and prismatic battery cells used in mobile devices and consumer electronics from damage caused by over-heating and over-currents.

In normal operation, current passes through the bi-metal contact because of its low contact resistance. During an abnormal event, the device reacts to the rise in cell temperature, causing the bi-metal contact to open at the specified temperature and its contact resistance to increase. At this point, the current shunts to the lower resistance PPTC, which acts as a heater and helps keep the bi-metal protector open and in a latched position until the fault is removed.

The combination of small form factors, high cell capacities and high battery discharge rates typical of LiP and prismatic battery protection applications demands a circuit protection device with low thermal cut-off temperatures (less than 90 degree C), high hold current ratings (above 6.0A) and a compact size, explains Littelfuse. Compared with other devices of this type, the MHP–TAC series offers higher voltage ratings, higher hold currents, more temperature rating options, and a thinner, smaller form factor, which reduces battery pack design space requirements, according to Littelfuse.

Typical applications for MHP-TAC series resettable over-temperature protection devices include LiP and prismatic battery cells intended for use in battery-powered devices such as notebook PCs, ultrabooks, tablets, smartphones and e-cigarettes.

The MHP-TAC devices measure 4.75 x 2.80 x 0.80mm, making them the smallest over-temperature protection device available for Li-Ion battery cells today, claims Littelfuse. They can help battery manufacturers save design space and weight, while ensuring the end product meets the heightened battery safety requirements, required by today’s consumers.

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