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User’s Manual 109

APPENDIX C. POWER SUPPLY

Appendix C provides information on the current requirements of

the RCM4000, and includes some background on the chip select

circuit used in power management.

C.1 Power Supplies

The RCM4000 requires a regulated 3.0 V – 3.6 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 RCM4000 board through header J2.

An RCM4000 with no loading at the outputs operating at 58.98 MHz typically draws

110 mA.

C.1.1 Battery-Backup Circuits

The RCM4000 does not have a battery, but there is provision for a customer-supplied bat-

tery to back up the data SRAM and keep the internal Rabbit 4000 real-time clock running.

Header J2, 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 4000 real-time clock to retain data with the RCM4000 powered down.

Figure C-1. External Battery Connections

at Header J2

A lithium battery with a nominal voltage of 3 V and a minimum capacity of 165

mA·h

recommended. A lithium battery is strongly recommended because of its nearly constant

nominal voltage over most of its life.

VBAT_EXT

GND

External

Battery

+3.3 V_IN

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