Resettable over-temperature protection for batteries

Resettable over-temperature protection for batteries

New Products |
By Nick Flaherty

The MHP–TAC (Metal Hybrid PPTC – Thermal Activated Compact) devices combine a PPTC (Polymeric Positive Temperature Coefficient) device in parallel with a bimetal protector (a resettable thermal cut-off device) to protect the cells used in mobile devices and consumer electronics from damage caused by overheating and overcurrents.

In normal operation, current passes through the bimetal contact because of its low contact resistance. During an abnormal event, the device reacts to the rise in cell temperature, causing the bimetal 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 bimetal 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 (<90 ºC), high hold current ratings (>6A) and a compact size. When 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.

Typical applications include notebook PCs, ultra-books, tablets, smart phones and e-cigarettes.

“At just 4.75mm x 2.80mm x 0.80mm, the MHP-TAC Series is the smallest overtemperature protection device available for lithium-ion battery cells used in today’s mobile devices and consumer electronics,” said Amy Chu, Product Manager, Electronics Business Unit at Littelfuse. “Not only can it help our battery manufacturer customers save valuable design space and weight, but it helps their products meet today’s heightened battery safety requirements.”

High voltage and high current ratings and low resistance ensures the MHP-TAC Series is capable of handling the battery voltages and battery charge/discharge currents common in high-capacity lithium-ion polymer and prismatic cells. The thin, compact form factor saves space, simplifying circuit protection in ultra-thin battery pack designs. 

The welding extension leads can also be customized to a specific battery design.​

The MHP-TAC Over-temperature Protection Devices are available in bulk in quantities of 1,000, with samples available via Littelfuse distributors worldwide.

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