Appendix D. Power Supply

Appendix D provides information on the current requirements of the RCM3000, and includes some background on the chip select circuit used in power management.

D.1 Power Supplies

The RCM3000 requires a regulated 3.3 V ± 0.15 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 RCM3000 Series board through header J2.

An RCM3000 with no loading at the outputs operating at 29.4 MHz typically draws 145 mA. The RCM3000 will consume an additional 10 mA when the programming cable is used to connect the programming header, J3, to a PC.

D.1.1 Battery-Backup Circuits

The RCM3000 does not have a battery, but there is provision for a customer-supplied battery to back up SRAM and keep the internal Rabbit 3000 real-time clock running.

Header J2, shown in Figure D-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 internal Rabbit 3000 real-time clock to retain data with the RCM3000 powered down.

Figure D-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.

The drain on the battery by the RCM3000 is typically 5 µA when no other power is supplied. If a 165 mA·h battery is used, the battery can last more than 3 years:

The actual life in your application will depend on the current drawn by components not on the RCM3000 and the storage capacity of the battery. Note that the shelf life of a lithium ion battery is ultimately 10 years. The RCM3000 does not drain the battery while it is powered up normally.

D.1.2 Reset Generator

The RCM3000 uses a reset generator to reset the Rabbit 3000 microprocessor when the voltage drops below the voltage necessary for reliable operation. The reset occurs between 2.85 V and 3.00 V, typically 2.93 V. The RCM3000 has a reset output, pin 1 on header J2.

D.2 Optional +5 V Output

The RCM3000 Series RabbitCore boards have an onboard charge pump that provides the +5 V needed by the RealTek Ethernet chip.

There is provision to have the +5 V supply available on pin 33 of header J2, but the default configuration for the 0 W surface-mounted jumpers does not bring out this option. Consult your Z-World or Rabbit Semiconductor sales representative for more information on quantity orders for this option. If the +5 V output option is enabled, you will be able to draw up to 40 mA.