User Manual
Table Of Contents
- 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 / Preliminary
s
XT55/56_hd_v02.96 Page 29 of 125 18.08.2005
3.2 Power Supply
The power supply for the GSM part of the XT55/56 module has to be a single voltage source
of V
GSM_BATT
+= 3.3V...4.8V. It must be able to provide sufficient current in a transmit burst
which typically rises to 1.6A.
All the key functions for supplying power to the device are handled by an ASIC power supply.
The ASIC provides the following features:
• Stabilizes the supply voltages for the GSM baseband using low drop linear voltage
regulators.
• Controls the module's power up and power down procedures.
A watchdog logic implemented in the baseband processor periodically sends signals to
the ASIC, allowing it to maintain the supply voltage for all digital XT55/56 components.
Whenever the watchdog pulses fail to arrive constantly, the module is turned off.
• Delivers, across the GSM_VDD pin, a regulated voltage of 2.9V. The output voltage
GSM_VDD may be used to supply, for example, an external LED or a level shifter.
However, the external circuitry must not cause any spikes or glitches on voltage
GSM_VDD. This voltage is not available in POWER DOWN mode. Therefore, the
GSM_VDD pin can be used to indicate whether or not GSM part of the XT55/56 module
is in POWER DOWN mode.
• Provides power to the SIM interface.
The RF power amplifier is driven directly from GSM_BATT+.
3.2.1 Power Supply Pins on the Board-to-Board Connector
Five GSM_BATT+ pins of the board-to-board connector are dedicated to connect the supply
voltage, five GND pins are recommended for grounding. The values stated below must be
measured directly at the reference points on the XT55/56 board (TP GSM_BATT+ and TP
GND illustrated in Figure 50).
The GSM_POWER and GSM_CHARGE pins serve as control signals for charging a Li-Ion
battery. GSM_VDDLP can be used to back up the RTC.
Table 4: Power supply pins of board-to-board connector
Signal name I/O Description Parameter
GSM_BATT+ I/O Positive operating voltage
Reference points are the
test points
3.3 V...4.8 V, I
typ
≤ 1.6 A during transmit burst
The minimum operating voltage must not fall
below 3.3 V, not even in case of voltage
drop.
GND - Ground 0 V
GSM_POWER I This line signals to the
processor that the
charger is connected.
GSM_CHARGE O Control signal for external
charging transistor
GSM_VDDLP I/O Can be used to back up
the RTC when V
GSM_BATT+
is not applied.
See Chapter 3.8
U
OUT,max
< V
GSM_BATT+
U
IN
= 2.0 V...5.5 V
R
i
= 1kΩ
I
in,max
= 30µA