MC75i Hardware Interface Description
3.2 Power Supply
71
MC75i_HD_v01.100a
Page 26 of 122
2009-08-13
Confidential / Released
Example: If the length of the flex cable reaches the maximum length of 100mm, this connection
may cause, for example, a resistance of 30m
in the BATT+ line and 30m
in the GND line.
As a result, a 2A transmit burst would add up to a total voltage drop of 120mV. Plus, if a battery
pack is involved, further losses may occur due to the resistance across the battery lines and
the internal resistance of the battery including its protection circuit.
Figure 3:
Power supply limits during transmit burst
3.2.2
Measuring the Supply Voltage V
BATT+
The reference points for measuring the supply voltage V
BATT+
on the module are BATT+ and
GND as illustrated in the figure below. BATT+ can be any of the five BATT+ pins on the board-
to-board connector.
Figure 4:
Position of the reference points BATT+ and GND
3.2.3
Monitoring Power Supply by AT Command
To monitor the supply voltage you can also use the AT^SBV command which returns the value
related to the reference points BATT+ and GND.
The module continuously measures the voltage at intervals depending on the operating mode
of the RF interface. The duration of measuring ranges from 0.5s in TALK/DATA mode to 50s
when MC75i is in IDLE mode or Limited Service (deregistered). The displayed voltage (in mV)
is averaged over the last measuring period before the AT^SBV command was executed.
Reference point
GND
Reference point
BATT+
