LISA-U1 series - System Integration Manual
3G.G2-HW-10002-3
Preliminary
System description
Page 25 of 125
1.5.3
Current consumption profiles
During operation, the current drawn by the LISA-U1 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 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).
During a GSM call, current consumption is in the order of 100-200 mA in receiving or in monitor bursts and is
about 30-50 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 current consumption profile of the data module in GSM talk mode is shown in Figure 10.
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]
200 mA
~125 mA
2500 mA
Peak current
depends on
TX power
GSM frame
4.615 ms
(1 frame = 8 slots)
1.5
1.0
0.5
0.0
2.5
2.0
~125 mA
~25 mA
Figure 10: VCC current consumption profile versus time during a GSM call (1 TX slot, 1 RX slot), with VCC=3.8 V
When a GPRS connection is established there is a different VCC current consumption profile also determined by
the transmitting and receiving bursts. In contrast to a GSM call, during a GPRS connection more than one slot
can be used to transmit and/or more than one slot can be used to receive. The transmitted power depends on
network conditions, which set the peak current consumption, but following the GPRS specifications the
maximum transmitted RF power is reduced if more than one slot is used to transmit, so the maximum peak of
current consumption is not as high as can be in case of a GSM call.
If the module transmits in GPRS class 12 connected mode in the GSM 850 or in the E-GSM 900 band at the
maximum power control level (27 dBm typical transmitted power in the transmit slot/burst), the current
consumption can reach up to 1400 mA (with unmatched antenna). This happens for 2.307 ms (width of the 4
transmit slots/bursts) with a periodicity of 4.615 ms (width of 1 frame = 8 slots/bursts), so with a 1/2 duty cycle,
according to GSM TDMA.
