Rabbit RabbitCore RCM2200, User Manual

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User’s Manual 71
A
PPENDIX
C. P
OWER
S
UPPLY
Appendix C provides information on the current requirements of
the RCM2200, and includes some background on the chip select
circuit used in power management.
C.1 Power Supplies
The RCM2200 requires a regulated 5 V ± 0.25 V DC power source. The RabbitCore
design presumes that the voltage regulator is on the user board, and that the power is made
available to the RabbitCore board through headers J4 and J5.
An RCM2200 with no loading at the outputs operating at 22.1 MHz typically draws 134 mA.
The RCM2200 will consume an additional 10 mA when the programming cable is used to
connect the programming header, J1, to a PC.
C.1.1 Battery-Backup Circuits
The RCM2200 does not have a battery, but there is provision for a customer-supplied bat-
tery to back up SRAM and keep the internal Rabbit 2000 real-time clock running.
Header J5, shown in Figure C-1, allows access to the external battery. This header makes
it possible to connect an external 3 V power supply. This allows the SRAM and the inter-
nal Rabbit 2000 real-time clock to retain data with the RCM2200 powered down.
Figure C-1. External Battery Connections
at Header J5
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.
D0
VCC
24
25
23
26
VBAT
GND
External
Battery