User`s manual

64 RabbitCore RCM2000
The drain on the battery by the RCM2000 is typically 10 µA when no other power is sup-
plied. If a 950 mA·h battery is used, the battery can last more than 6 years:
Since the shelf life of the battery is 10 years, the battery can last for its full shelf life. The
actual life in your application will depend on the current drawn by components not on the
RCM2000 and the storage capacity of the battery.
C.1.2 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
the current consumed by the real-time clock and lengthening the battery life.
• 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
when the voltage begins to drop.
VRAM and Vcc are nearly equal (<100 mV, typically 10 mV) when power is supplied to
the RCM2000.
Figure C-2 shows the RCM2000 battery-backup circuit.
Figure C-2. RCM2000 Battery-Backup Circuit
VRAM is also available on pin 34 of header J2 to facilitate battery backup of the external
circuit. Note that the recommended minimum resistive load at VRAM is 100 kΩ, and new
battery life calculations should be done to take external loading into account.
950 mA·h
10 µA
------------------------ 10.8 years (shelf life = 10 years).=
R11
10 kW
VRAM
VBAT-EXT
External Battery
R12
47 kW
2 kW
R14
RT1
22 kW
mPBAT
Vcc
22 kW
R7
47 kW
U5
pin 5
R8
D2
D1
D3
T
thermistor
C19
1 nF
C9
1 nF