User's Manual

MC55/56 Hardware Interface Description
Confidential / Preliminary
s
MC55/56_hd_v03.00 Page 25 of 104 16.08.2005
3.2 Power supply
The power supply of MC55/56 has to be a single voltage source of V
BATT
+= 3.3V...4.8V. It
must be able to provide sufficient current in a transmit burst which typically rises to 2A.
Beyond that, the power supply must be able to account for increased current consumption if
the module is exposed to inappropriate conditions, for example antenna mismatch. For
further details see Chapters 3.2.2 and 5.4.1.
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 MC55/56 components.
Whenever the watchdog pulses fail to arrive constantly, the module is turned off.
• Delivers, across the VDD pin, a regulated voltage of 2.9V. The output voltage 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 VDD. This voltage is not
available in POWER DOWN mode. Therefore, the VDD pin can be used to indicate
whether or not MC55/56 is in POWER DOWN mode.
• Provides power to the SIM interface.
The RF power amplifier is driven directly from BATT+.
3.2.1 Power supply pins on the board-to-board connector
Five 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 MC55/56 board (TP BATT+ and TP GND
illustrated in Figure 39).
The POWER and CHARGE pins serve as control signals for charging a Li-Ion battery.
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
BATT+ I/O Positive operating voltage
Reference points are the
test points
3.3 V...4.8 V, I
typ
≤ 2 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
POWER I This line signals to the
processor that the charger
is connected.
CHARGE O Control signal for external
charging transistor
VDDLP I/O Can be used to back up
the RTC when V
BATT+
is not
applied.
See Chapter 3.8
U
OUT,max
< V
BATT+
U
IN
= 2.0 V...5.5 V
R
i
= 1kΩ
I
in,max
= 30µA