Data Sheet

Summary AN1012

24/33 Doc ID 6395 Rev 4

10 Summary

Battery life and data retention for ZEROPOWER

and TIMEKEEPER

products are

primarily functions of two factors:

● Capacity consumption, and

● Storage life of the lithium button cell battery.

Due to the fact that storage life (caused by electrolyte evaporation) has little effect at

temperatures below 60 °C, the data retention of most applications will be dependent upon

the I

CCDR

of the SRAM being backed-up, as well as the V

duty cycle. This allows a fairly

simple calculation (see Section 3.4: Calculating capacity consumption on page 10) to be

used to determine the lifetime.

All ST ZEROPOWER products are able to offer at least a 10 year data retention life, typically

at 40 °C. This may be increased by reducing the temperature, increasing the V

duty cycle,

or in the case of the surface mount SNAPHAT

products, using the larger 120 mAh

SNAPHAT top.

For the TIMEKEEPER family, battery lifetimes are also affected by the percentage of time

the oscillator is in operation. Commercial devices fabricated in 4T technologies provide

7 years of continuous operation at 20 °C using the 48 mAh M4T28-BR12SH SNAPHAT top,

and typically greater than 15 years with the 120 mAh M4T32-BR12SH SNAPHAT top.

The ZEROPOWER and TIMEKEEPER supervisor families allow the user to purchase

commodity SRAMs at the best available market price. However, overall data retention life

will be determined by the I

CCDR

of the SRAM selected.