LISA-U2 series - System integration manual
UBX-13001118 - R27
System description
Page 28 of 183
C1-Public
1.5.3
Current consumption profiles
During operation, the current drawn by the LISA-U2 series modules through the
VCC
pins can vary by
several orders of magnitude. This ranges from the high peak of current consumption during GSM
transmitting bursts at maximum power level in 2G connected mode, to a continuous high current
drawn in UMTS connected mode, to the low current consumption during power saving in idle mode.
1.5.3.1
2G connected mode
When a GSM call is established, the
VCC
consumption is determined by the current consumption
profile typical of the GSM transmitting and receiving bursts.
The current consumption peak during a transmission slot is strictly dependent on the transmitted
power, which is regulated by the network. If the module is transmitting in GSM talk mode in the GSM
850 or in the E-GSM 900 band and at the maximum RF power control level (approximately 2 W or 33
dBm in the allocated transmit slot/burst) the current consumption can reach up to 2500 mA (with a
highly unmatched antenna) for 576.9 µs (width of the transmit slot/burst) with a periodicity of 4.615
ms (width of 1 frame = 8 slots/burst), so with a 1/8 duty cycle according to GSM TDMA (Time Division
Multiple Access). If the module is in GSM connected mode in the DCS 1800 or in the PCS 1900 band,
the current consumption figures are lower than the one in the GSM 850 or in the E-GSM 900 band,
due to 3GPP transmitter output power specifications (see the LISA-U2 series data sheet
During a GSM call, current consumption is in the order of 60-130 mA in receiving or in monitor bursts
and is about 10-40 mA in the inactive unused bursts (low current period). The more relevant
contribution to determine the average current consumption is set by the transmitted power in the
transmit slot.
An example of the current consumption profile of the data module in GSM talk mode is shown in the
Time [ms]
RX
slot
unused
slot
unused
slot
TX
slot
unused
slot
unused
slot
MON
slot
unused
slot
RX
slot
unused
slot
unused
slot
TX
slot
unused
slot
unused
slot
MON
slot
unused
slot
GSM frame
4.615 ms
(1 frame = 8 slots)
Current [A]
Peak current
depends on TX
power and actual
antenna load
GSM frame
4.615 ms
(1 frame = 8 slots)
1.5
1.0
0.5
0.0
2.5
2.0
Figure 11: VCC current consumption profile versus time during a GSM call (1 TX slot, 1 RX slot)