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March 2012 Doc ID 6254 Rev 4 1/11
AN1011
Application note
Battery technology used in NVRAM
and real-time clock (RTC) products from ST
Introduction
Lithium Carbon MonoFlouride (LiCFx) batteries are used by STMicroelectronics in their
ZEROPOWER
®
and TIMEKEEPER
®
NVRAM devices and in their serial real-time clock
(RTC) devices. The batteries provide the backup power to maintain the static RAM arrays
and to keep the oscillators running in the TIMEKEEPER and serial RTC devices.
When the discharge rates are low, these non-rechargeable lithium batteries are capable of
maintaining a highly reliable voltage level for many years. Lithium batteries, therefore, are
used for a variety of applications that require battery backup without need of maintenance
for many years.
To be used in electronic components, these cells also need to be composed of constituents
that are nontoxic, non-corrosive, and non-explosive. They also must be chemically and
thermally stable before, during and after discharge. STMicroelectronics utilizes the 48 mAh
BR1225X cell, and the 120 mAh BR1632 cell. The electrolyte of these cells (see Figure 1) is
based on an organic solvent, instead of a corrosive alkaline or acidic solution found in most
conventional batteries. This greatly improves the cell’s leakage resistance and guards
against the negative effects caused by leakage.
Figure 1. Cell cross-section
(+)
(-)
AI02531
Gasket
CFx Cathode
Current Cathode Separator and Electrolyte
Lithium Anode
Anode Cap
Cell Can
www.st.com
