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

(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