RabbitCore RCM2200, Руководство пользователя

Страница: 37 / 60

User’s Manual Power Supply B–1
Power Supply B
Appendix B provides information on the current requirements of the RabbitCore
RCM2200, and some background on the chip select circuit used in power manage-
ment.
B.1 Power Supplies
The RabbitCore 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.
A RabbitCore RCM2200 with no loading at the out-
puts operating at 22.1 MHz typically draws 134 mA.
The RabbitCore RCM2200 will consume an addi-
tional 10 mA when the programming cable is used
to connect J1 to a PC.
B.2 Battery Backup Circuits
As explained in Section 2.3.2, the RabbitCore
RCM2200 has provision for battery backup, which
kicks in to keep VRAM from dropping below 2 V.
The current drain on the battery in a battery-backed
circuit must be kept to a minimum. When the Rab-
bitCore RCM2200 is not powered, the battery keeps
the SRAM memory contents and the real-time clock
(RTC) going. The SRAM has a powerdown mode
that greatly reduces power consumption. This pow-
erdown mode is activated by raising the chip select
(CS) signal line. Normally the SRAM requires Vcc
to operate. However, only 2 V is required for data
retention in powerdown mode. Thus, when power is
removed from the circuit, the battery voltage needs
to be provided to both the SRAM power pin and to
the CS signal line. The CS control switch accom-
plishes this task for the CS signal line.
Figure B–1 shows a schematic of the chip select
control switch.