SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26 System description
Page 26 of 217
1.5.1.2 VCC current consumption in 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. The transmitted power in the transmit slot is also the more relevant factor for
determining the average current consumption.
If the module is transmitting in 2G single-slot mode (as in GSM talk mode) in the 850 or 900 MHz bands, at the
maximum RF power control level (approximately 2 W or 33 dBm in the Tx slot/burst), the current consumption
can reach a high peak / pulse (see the SARA-G3 series Data Sheet [1] and the SARA-U2 series Data Sheet [2]) 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 transmitting in 2G single-slot mode in the 1800 or 1900 MHz bands, the current consumption
figures are quite less high than the one in the low bands, due to the 3GPP transmitter output power
specifications.
During a GSM call, current consumption is not so significantly high in receiving or in monitor bursts and it is low
in the bursts unused to transmit / receive.
Figure 9 shows an example of the module current consumption profile versus time in GSM talk mode.
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
60-120 mA
1900 mA
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
2.0
60-120 mA
10-40 mA
Figure 9: VCC current consumption profile versus time during a GSM call (1 TX slot, 1 RX slot)
Figure 10 illustrates the VCC voltage profile versus time during a GSM call, according to the related VCC current
consumption profile described in Figure 9.
Time
undershoot
overshoot
ripple
drop
Voltage
3.8 V
(typ)
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)
GSM frame
4.615 ms
(1 frame = 8 slots)
Figure 10: Description of the VCC voltage profile versus time during a GSM call (1 TX slot, 1 RX slot)
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