Z-World RabbitCore User Manual - Ppendix

User’s Manual

123

A

PPENDIX

 D.  P

OWER

 S

UPPLY

Appendix D provides information on the current requirements

of the RCM3600, and includes some background on the chip

select circuit used in power management.

D.1  Power Supplies

Power is supplied from the motherboard to which the RCM3600 is connected via  header 

J1. The RCM3600 has an onboard +3.3 V linear power regulator that provides the +3.3 V 

supply to operate the RCM3600. Figure D-1 shows the power-supply circuit.

Figure D-1.  RCM3600 Power Supply

The input voltage should be 5 V ± 0.25 V DC. An RCM3600 with no loading at the outputs 

typically draws 60 mA when operating at 22.1 MHz. Take care that any DC loading (for 

example, sourcing digital outputs) does not increase the overall current to more than 190 

mA to keep the +3.3 V linear regulator from overheating.

D.1.1  Battery-Backup Circuits

The RCM3600 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 3000 real-time clock running.

Header J1, shown in Figure D-1, allows access to the external battery. This header makes 

it possible to connect an external 3 V battery. This allows the SRAM and the internal Rab-

bit 3000 real-time clock to retain data with the RCM3600 powered down.

LINEAR POWER REGULATOR

POWER

IN

J1

10 µF

LM1117

U7

+3.3 V

3

1

2

38

39

40

10 µF

VIN

37

VBAT_EXT

External

Battery