1997-10-13 , E/IC-843/540

In a market where small size/weight and long standby/talk times are key selling features of mobile phones, manufacturers are turning to LiIon (Lithium-Ion) batteries as a solution to these two conflicting requirements. However, although LiIon batteries allow the design of lightweight single-cell battery packs, their critical charging requirements pose significant safety and reliability problems. If short-circuited, these batteries present a severe fire and explosion hazard. If incorrectly charged or discharged, their energy storage capacity can be seriously impaired.

At Power '97, the world's premier event for introducing new power solutions for wireless communications, Philips Semiconductors is launching a brand new safety IC that protects LiIon battery packs against misuse. The  SAA1502A Safety IC, which is designed to be built into the battery pack, provides effective current limiting during both charging and discharging of the LiIon cell. In addition, it automatically disconnects the battery pack if the cell approaches either an over-charge or deep discharge state - conditions that inevitably impair the cell's recharge cycle life and at worst can lead to a severe safety hazard.

Compared to most other safety ICs on the market, the SAA1502A has the ability to start up correctly from a zero-voltage condition. As a result, it does not require LiIon cells to be pre- charged before they are assembled into the battery pack. This not only simplifies battery pack assembly, it also significantly reduces manufacturing costs and eliminates the hazard of working with partly charged batteries.

Fabricated as a multi-chip module, the SAA1502A incorporates a BCD PowerLogic controller and a TrenchMOS dual power MOSFET chip. Because this construction places the controller and power MOSFETs in close thermal proximity, the over-temperature protection in the controller also protects the MOSFETs against thermal runaway. In addition, the SAA1502A's over-current protection in both charging and discharging modes means that both MOSFETs remain constantly within their safe operating area. These features combine to make the SAA1502A considerably more reliable than competing solutions that use discrete MOSFET devices.

The very low on-resistance of the TrenchMOS devices (typically less than 60 mW) and the extremely low power consumption of the BCD PowerLogic controller (typically 7 µA in normal operation and only 0.1 µA when in deep discharge protection mode) mean that the SAA1502A introduces negligible power loss into the battery pack.

The SAA1502A is packaged in a 16-lead small-outline surface-mount package. Samples are available now, with volume production scheduled to begin by the end of this year.

Philips Semiconductors, a division of Philips Electronics NV, headquartered in Eindhoven, The Netherlands, is the ninth largest semiconductor supplier in the world and the third largest supplier of discretes in the world. Philips Semiconductors' innovations in digital audio, video, and mobile technology position the company as a leader in the consumer, multimedia and wireless communications markets. Sales offices are located in all major markets around the world and are supported by systems labs.

TrenchMOS and BCD PowerLogic are registered trademarks of Philips Semiconductors.

Power '97, The Fifth International Conference on Power Requirements for Mobile Computing and Wireless Communication (October 12 -15, Santa Clara, California, USA) is a highly specialist exhibition that provides manufacturers of portable computing and cellular communication devices with the opportunity to keep pace with the latest hardware and software developments in power supplies and power management for mobile products and services. The conference, for which Philips Semiconductors is one of nine sponsors, has attracted some 700 delegates from around the world. Its extensive program of technical papers is accompanied by an exhibition of products and services.