AT&T 3B2/300 Technical Reference Manual page 568

- - - - - - - - - - - - - - - - - - - - - - - - - - - FUNCTIONAL DESCRIPTION
3B2 Computer Backup Battery Supply
Figure 3-103 is a functional block diagram of the 382 computer Backup Battery Supply. A 3.6 volt
DC high energy lithium battery is used to supply approximately 3.3 volt DC standby power for the
following:
• Time-of-Day Clock
• Nonvolatile Random Access Memory (NVRAM)
• Feature Card Slots.
A reverse biased diode isolates the battery from the connecting circuits when VCC and +12 volt DC
are applied to the system board. A small leakage current of approximately 100 microamperes serves to
maintain the battery in the fresh state while the external power is applied. When VCC and 12 volt DC
are absent, the battery supplies approximately 3.0 volt DC to the connecting circuits. The expected
battery life is approximately six years if only the system board current drain is considered.* The battery
life will be less than six years depending on the amount of standby current drawn by the feature cards.
FEATURE CARD BATTERY
CURRENT DRAIN LIFE
(microamperes) (Years)
0 6.0
10 4.0
20 3.0
30 2.4
40 2.0
50 1.5
60 1.1
*
Some of the newer 3B2/400 computers may use Performance Semiconductor P4Cl48L-35 (lK by 4 bits) Static Random Access
Memory (SRAM) which will decrease this "system board only" lifetime to about 4.8 years.
FUNCTIONAL DESCRIPTION 3-315