Siemens TC65 - Monitoring Power Supply by at Command; Measuring the Supply Voltage V; Batt; Figure 3: Power Supply Limits During Transmit Burst

TC65 Hardware Interface Description
Strictly confidential / Draft
s
TC65_HD_V00.521 Page 25 of 99 24.05.2005
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, both accessible at a capacitor located close to the board-to-board connector of the
module.
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 TC65 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.
Transmit
burst 2A
Transmit
burst 2A
Ripple
Drop
min. 3.2V
BATT+
Reference
point
BATT+
Reference
point GND