User's Manual
Table Of Contents
- Contents
- Figures
- Tables
- Document history
- Introduction
- Product concept
- GSM application interface
- GSM/GPRS operating modes
- Power supply
- Power up / down scenarios
- Automatic GPRS Multislot Class change
- Charging control of the GSM part
- Power saving
- Summary of state transitions (except SLEEP mode)
- RTC backup for GSM part of XT55/56
- Serial interfaces of the XT55/56 GSM part
- Audio interfaces
- SIM interface
- Control signals
- GPS application interface
- GSM and GPS antenna interfaces
- Electrical, reliability and radio characteristics
- Mechanics
- Reference approval
- Example applications
- List of parts and accessories
XT55/56 Hardware Interface Description
Confidential / Released
s
XT55/56_hd_v02.06a Page 29 of 125 17.12.2004
3.2.2 Minimizing power losses
When designing the power supply for your application please pay specific attention to power
losses. Ensure that the input voltage V
GSM_BATT+
never drops below 3.3V on the GSM part of
the XT55/56 board, not even in a transmit burst where current consumption can rise to
typical peaks of 1.6A. It should be noted that the GSM part of the XT55/56 module switches
off when exceeding these limits. Any voltage drops that may occur in a transmit burst should
not exceed 400mV. For further details see Chapter 6.4.
The best approach to reducing voltage drops is to use a board-to-board connection as
recommended, and a low impedance power source. The resistance of the power supply lines
on the host board and of a battery pack should also be considered.
Note: If the application design requires an adapter cable between both board-to-board
connectors, use a cable as short as possible in order to minimize power losses.
Example: If the length of the cable reaches the maximum length of 200mm, this connection
may cause, for example, a resistance of 50m in the GSM_BATT+ line and
50m in the GND line. As a result, a 1.6A transmit burst would add up to a total
voltage drop of 160mV. 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 protective circuit.
Transmit
burst 1.6A
Transmit
burst 1.6A
Ripple
Drop
min. 3.3V
GSM_BATT+
Figure 2: Power supply limits during transmit burst
The input voltage V
GSM_BATT+
must be measured directly at the test points on the XT55/56
board (TP GSM_BATT+ and TP GND illustrated in Figure 50).
3.2.3 Monitoring power supply
To help you monitor the supply voltage you can use the AT^SBV command which returns the
voltage measured at TP GSM_BATT+ and GND.
The voltage is continuously measured at intervals depending on the operating mode on the
RF interface. The duration of measuring ranges from 0.5s in TALK/DATA mode up to 50s
when the GSM part of the XT55/56 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.
For details please refer to [1].