BL4S200 User’s Manual
179
The digital ground and the analog ground share a single split ground plane on the board,
with the analog ground connected at a single point to the digital ground by a 0
resistor
(R95). 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 a Micro-
Fit
®
connector at J12.
B.1.1 Power for Analog Circuits
Power to the analog circuits is provided by way of a one-stage low-pass filter, which
isolates the analog section from digital noise generated by the other components. The ana-
log +3.3 V supply powers the D/A converter, and is not accessible to the user. The A/D
converter is powered by the reg3.3 V supply, and supplies the +2.5 V reference
violate from which the 1.116 V, 1.95 V, and 3.00 V reference voltages for the D/A con-
verter output circuits are derived.
NOTE:
The +12 V power supplies used to drive the analog outputs only have sufficient
current output in their design to supply the analog output channels. Do not use these
voltage supplies for other applications.
B.2 Batteries and External Battery Connections
The SRAM and the real-time clock on the BL4S200 modules 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 BL4S200 is powered or not. When the
BL4S200 is powered normally, and the +3.3 V supply is within operating limits, the
SRAM and the real-time clock are powered from the +3.3 V supply. If power to the board
is lost or falls below 2.93 V, the VRAM and real-time clock power will come from the bat-
tery. The reset generator circuit controls the source of power by way of its
/RESET
output
signal.
A replaceable 235 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 typi-
cally less than 10 µA when there is no external power applied to the BL4S200, and so the
expected shelf life of the battery is
The actual battery life in your application will depend on the current drawn by components
not on the BL4S200 and on the storage capacity of the battery. The BL4S200 does not
drain the battery while it is powered up normally.
235 mA·h
10 µA
------------------------
2.7 years.
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