Installation Instructions

LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 28 of 175
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, the current consumption can reach up to 1600 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. If the module is in GPRS connected mode in
the DCS 1800 or in the PCS 1900 band, the current consumption figures are lower than in the GSM 850 or in
the E-GSM 900 band, due to 3GPP transmitter output power specifications (see LISA-U2 series Data Sheet [1]).
Figure 12 reports the current consumption profiles in GPRS class 12 connected mode, in the GSM 850 or in the
E-GSM 900 band, with 4 slots used to transmit and 1 slot used to receive.
Time [ms]
RX
slot
unused
slot
TX
slot
TX
slot
TX
slot
TX
slot
MON
slot
unused
slot
RX
slot
unused
slot
TX
slot
TX
slot
TX
slot
TX
slot
MON
slot
unused
slot
GSM frame
4.615 ms
(1 frame = 8 slots)
Current [A]
GSM frame
4.615 ms
(1 frame = 8 slots)
1.5
1.0
0.5
0.0
2.5
2.0
Peak current depends
on TX power and
actual antenna load
Figure 12: VCC current consumption profile versus time during a GPRS/EDGE connection (4TX slots, 1 RX slot)
In case of EDGE connections the VCC current consumption profile is very similar to the GPRS current profile, so
the image shown in Figure 12, representing the current consumption profile in GPRS class 12 connected mode,
is valid for the EDGE class 12 connected mode as well.