Motorola V186 - Cell Phone - GSM System Planner Manual page 73

The general equation for Vx is:
Vo depends on the power supply configuration. Vo should be 13 V DC when the backup
battery option is not used. If the battery option is used with the main power supply,
during power fail Vo depends on the battery voltage (which may be below 13 V DC). It is
highly recommended to use at least 11 V DC for input voltage Vx.
Consider the following example:
An expanded RTU includes five expansion frames.
The maximal accumulated current consumption of each expansion frame
(expansion module, I/O modules, floating power supply on modules, etc.) is
calculated.
The input voltage Vx of each expansion power supply (V1-V5) is calculated as
described above.
The input voltage at the first three expansion power supplies (V1,V2, V3) is above
11 V DC.
The input voltage at the last two expansion power supplies (V4, V5) is below 11 V
DC.
This means that from the voltage drop perspective, the first three expansion frames
can be cascaded to the power supply in the main frame, the expansion power supply
on the fourth expansion frame should be replaced with an AC or DC power supply
option and the fifth expansion power supply can be cascaded from the fourth frame
power supply.
IMPORTANT: Design note: The design must take into account the worst case result of
both the power consumption calculation and voltage drop calculations.
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I/O Expansion