101-1226 Rabbit Semiconductor, 101-1226 Datasheet - Page 162

• Manufacturer Part Number: 101-1226
• Description: RCM3900 DEV KIT UNIVERSAL
• Manufacturer: Rabbit Semiconductor
• Series: RabbitCore 3900r
• Type: MPU Moduler

Specifications of 101-1226

• Contents: RabbitCore Module, Dev. Board, AC Adapter, Cable and Dynamic C® CD-Rom
• For Use With/related Products: RCM3900
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 316-1137

A lithium battery with a nominal voltage of 3 V and a minimum capacity of 165 mA·h is
recommended. A lithium battery is strongly recommended because of its nearly constant
nominal voltage over most of its life.
The drain on the battery by the RCM3900 is typically 6 µA when no other power is sup-
plied. If a 235 mA·h battery is used, the battery can last about 4.5 years:
The actual battery life in your application will depend on the current drawn by components
not on the RCM3900 and the storage capacity of the battery. The RCM3900 does not drain
the battery while it is powered up normally.
Cycle the main power off/on after you install a backup battery for the first time, and when-
ever you replace the battery. This step will minimize the current drawn by the real-time
clock oscillator circuit from the backup battery should the RCM3900 experience a loss of
main power.
Rabbit’s Technical Note TN235, External 32.768 kHz Oscillator Circuits, provides addi-
tional information about the current draw by the real-time clock oscillator circuit.
D.1.2 Battery-Backup Circuit
Figure D-2 shows the battery-backup circuit.
The battery-backup circuit serves three purposes:
• It reduces the battery voltage to the SRAM and to the real-time clock, thereby limiting
• It ensures that current can flow only out of the battery to prevent charging the battery.
• A voltage, VOSC, is supplied to U5, which keeps the 32.768 kHz oscillator working
RabbitCore RCM3900 User’s Manual
the current consumed by the real-time clock and lengthening the battery life.
when the voltage begins to drop.
NOTE: Remember to cycle the main power off/on any time the RCM3900 is removed
235 mA·h
----------------------- -
from the Prototyping Board or motherboard since that is where the backup battery
would be located.
6 µA
=
Figure D-2. RCM3900 Backup Battery Circuit
4.5 years.
W
W
W
162