Installation Instructions
LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 29 of 175
1.5.3.2 3G connected mode
During a 3G connection, the module can transmit and receive continuously due to the Frequency Division Duplex
(FDD) mode of operation with the Wideband Code Division Multiple Access (WCDMA). The current consumption
depends again on output RF power, which is always regulated by network commands. These power control
commands are logically divided into a slot of 666 µs, thus the rate of power change can reach a maximum rate
of 1.5 kHz. There are no high current peaks as in the 2G connection, since transmission and reception are
continuously enabled due to FDD WCDMA implemented in the 3G that differs from the TDMA implemented in
the 2G case. In the worst scenario, corresponding to a continuous transmission and reception at maximum
output power (approximately 250 mW or 24 dBm), the current drawn by the module at the VCC pins is in the
order of continuous 500-800 mA (see LISA-U2 series Data Sheet [1] for detailed values). Even at lowest output
RF power (approximately 0.01 µW or -50 dBm), the current still remains in the order of 200 mA due to module
baseband processing and transceiver activity.
An example of current consumption profile of the data module in UMTS/HSxPA continuous transmission mode is
shown in Figure 13.
Time
[ms]
3G frame
10 ms
(1 frame = 15 slots)
Current [mA]
Current consumption
depends on TX power and
actual antenna load
170 mA
1 slot
666 µs
850 mA
0
300
200
100
500
400
600
700
800
Figure 13: VCC current consumption profile versus time during a UMTS/HSPA connection
When a packet data connection is established, the actual current profile depends on the amount of transmitted
packets; there might be some periods of inactivity between allocated slots where current consumption drops
about 100 mA. Alternatively, at higher data rates the transmitted power is likely to increase due to the higher
quality signal required by the network to cope with enhanced data speed.