Specifications

AC65/AC75 Hardware Interface Description
3.2 Power Supply
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AC65_AC75_HD_v01.002 Page 27 of 117 2006-10-30
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3.2 Power Supply
AC65/AC75 needs to be connected to a power supply at the B2B connector (5 pins each BATT+ and GND).
The power supply of AC65/AC75 has to be a single voltage source at BATT+. It must be able to provide the peak
current during the uplink transmission.
All the key functions for supplying power to the device are handled by the power management section of the ana-
log controller. This IC provides the following features:
•Stabilizes the supply voltages for the GSM baseband using low drop linear voltage regulators.
• Switches the module's power voltages for the power-up and -down procedures.
• Delivers, across the VEXT pin, a regulated voltage for an external application. This voltage is not available in
Power-down mode.
• SIM switch to provide SIM power supply.
3.2.1 Minimizing Power Losses
When designing the power supply for your application please pay specific attention to power losses. Ensure that
the input voltage V
BATT+
never drops below 3.3V on the AC65/AC75 board, not even in a transmit burst where
current consumption can rise to typical peaks of 2A. It should be noted that AC65/AC75 switches off when
exceeding these limits. Any voltage drops that may occur in a transmit burst should not exceed 400mV.
The measurement network monitors outburst and inburst values. The drop is the difference of both values. The
maximum drop (Dmax) since the last start of the module will be saved. In IDLE and SLEEP mode, the module
switches off if the minimum battery voltage (V
batt
min) is reached.
Example:
V
I
min = 3.3V
Dmax = 0.4V
V
batt
min = V
I
min + Dmax
V
batt
min = 3.3V + 0.4V = 3.7V
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 flex
cable as short as possible in order to minimize power losses.
Example:
If the length of the flex cable reaches the maximum length of 100mm, this connection may cause, for example,
a resistance of 30m
Ω in the BATT+ line and 30mΩ 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 resis-
tance across the battery lines and the internal resistance of the battery including its protection circuit.
Figure 3: Power supply limits during transmit burst