Metal Hybrid PPTC device offers smart activation feature

February 28, 2012 // By Paul Buckley
TE Circuit Protection, a business unit of TE Connectivity, has introduced a Metal Hybrid PPTC (MHP) device offering Smart Activation (SA) functionality. The MHP-SA device provides a resettable, cost-effective and space-saving alternative to typical methods of protecting high-power lithium battery and module applications.

The applications include cordless power tools, e-scooters and light electric vehicles (LEVs) and standby power and energy storage systems (ESSs).

The MHP-SA device helps provide overcharge protection in large multi-cell battery packs and modules in which circuit protection devices interface with electronics as part of a sophisticated battery management system. It's Smart Activation design feature accomplishes this via a third terminal signal line that enables external activation.      

In a typical scenario, an IC monitors the battery system's temperature, current and voltage and, if an abnormality is detected, it switches on a FET and activates the heater element (PPTC) of the MHP-SA device to heat the bimetal. The bimetal contacts then open and cut contact to the main line. The first in a series of planned devices, the MHP-SA50-400-M5 device has a 50-A/400-VDC maximum rating and its hold current is 50 A on the main line. The device can be activated electronically with as little as 3 A via the signal line.     

MHP technology utilizes a hybrid circuit protection approach, combining a bimetal protector in parallel with a polymeric positive temperature coefficient (PPTC) device. Resettable MHP technology offers excellent arc suppression characteristics and also offers a smaller size and thinner form factor compared to larger DC fuses or other protection devices.     

The MHP-SA device helps save design costs due to its ability to employ a low-power switch to open the main line, enabling lower-cost FETs to be installed. And because the MHP-SA device is resettable there is no need to overrate for inrush currents. In some cases, designers can replace larger, higher-cost DC fuses with an MHP-SA device.        

“Few protection solutions address high-rate-discharge battery applications, and traditional circuit protection techniques tend to be large, complex and/or expensive,” said Ty Bowman, TE Circuit Protection Global Battery Market Manager. “The MHP-SA device offers design benefits in multi-cell battery packs that conventional circuit protection approaches are unable to deliver. The