User`s manual

74 Wildcat (BL2000)
C.1.1 Power for Analog Circuits
Power to the analog circuits is provided by way of a two-stage low-pass filter, which iso-
lates the analog section from digital noise generated by the other components. The analog
power voltage +V powers the op-amp for the buffered A/D converter inputs, the A/D con-
verter, and the 4.096 V reference circuit. The two D/A converters can be powered either
from the reference, which is the standard, or from +V when ratiometric measurements are
desired. The maximum current draw on +V is less than 10 mA.
There are three digital grounds, one on each of the screw-terminal headers associated with
the digital functions (J2, J8, and J9). The digital ground and the analog ground share a sin-
gle split ground plane on the board, with the analog ground connected at a single point to
the digital ground by a 0 Ω resistor (R87). This is done to minimize digital noise in the
analog circuits and to eliminate the possibility of ground loops. External connections to
analog ground are made on screw-terminal header J4.
C.2 Batteries and External Battery Connections
The SRAM and the real-time clock have battery backup. Power to the SRAM and the real-
time clock (VRAM) is provided by two different sources, depending on whether the main
part of the BL2000 is powered or not. When the BL2000 is powered normally, and Vcc is
within operating limits, the SRAM and the real-time clock are powered from Vcc. If power
to the board is lost or falls below 4.63 V, the VRAM power will come from the battery. The
reset generator circuit controls the source of power by way of its /RESET output signal.
A replaceable 265 mA·h lithium battery provides power to the real-time clock and SRAM
when external power is removed from the circuit board. The drain on the battery is typically
less than 10 µA when there is no external power applied, and so the expected in-service life
of the battery is
The drain on the battery is typically less than 4 µA when external power is applied, and so
the expected BL2000 shelf life is
A long-life 950 mA·h solder-in battery is also provided for in the board layout. Alterna-
tively, an external battery may be connected to the BL2000 via header J12. The existing
battery does not have to be removed when an external battery is used.
265 mA·h
10 µA
------------------------ 3.0 years.=
265 mA·h
4 µA
------------------------ 7 . 5 y e a r s .=