RabbitCore RCM4100 User's Manual

Appendix C. Power Supply

Appendix C provides information on the current requirements of the RCM4100 series of modules, and includes some background on the chip select circuit used in power management.

C.1 Power Supplies

The RCM4100 series of modules 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 RCM4100 series of modules through header J2.

A module with no loading at the outputs operating at 58.98 MHz typically draws up to 125 mA.

C.1.1 Battery-Backup Circuits

The RCM4100 series of modules do not have a battery, but there is provision for a customer-supplied battery 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 internal Rabbit 4000 real-time clock to retain data with the module 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 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 RCM4110 is typically 7.5 µA when no other power is supplied. If a 165 mA·h battery is used, the battery can last about 2.5 years:

The actual life in your application will depend on the current drawn by components not on the RCM4100 series of modules and on the storage capacity of the battery. The RCM4100 series of modules does not drain the battery while it is powered up normally.

C.1.2 Reset Generator

The RCM4100 series of modules uses a reset generator to reset the Rabbit 4000 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. Since the RCM4100 modules will operate at voltages as low as 3.0 V, exercise care when operating close to the 3.0 V minimum voltage (for example, keep the power supply as close as possible to the RCM4100) since your RCM4100 could reset unintentionally.

The RCM4100 modules have a reset output, pin 3 on header J2.