LISA-U2 series - System integration manual
UBX-13001118 - R27
System description
Page 19 of 183
C1-Public
☞
The module cannot be switched on if the
VCC
voltage value is below the specified normal operating
range minimum limit. Ensure that the input voltage at
VCC
pins is above the minimum limit of the
normal operating range for more than 3 seconds after the start of the module switch-on sequence.
When LISA-U2 series modules are in operation, the voltage provided to
VCC
pins can exceed the
normal operating range limits but must be within the extended operating range limits specified in the
LISA-U2 series data sheet
. Occasional deviations from the ETSI specifications may occur when
the input voltage at the
VCC
pins is outside the normal operating range and is within the extended
operating range.
☞
LISA-U2 series modules switch off when the
VCC
voltage value drops below the specified extended
operating range minimum limit: ensure that the input voltage at the
VCC
pins never drops below
the minimum limit of the extended operating range when the module is switched on, not even
during a GSM transmit burst, where the current consumption can rise up to maximum peaks of
2.5 A in case of a mismatched antenna load.
⚠
Operation above the normal operating range maximum limit is not recommended and extended
exposure beyond it may affect device reliability.
⚠
Stress beyond the VCC absolute maximum ratings can cause permanent damage to the module:
if necessary, voltage spikes beyond the VCC absolute maximum ratings must be restricted to
values within the specified limits by using appropriate protection.
☞
When designing the power supply for the application, pay specific attention to power losses and
transients. The DC power supply must be able to provide a voltage profile to the
VCC
pins with the
following characteristics:
o
Voltage drop during transmit slots must be lower than 400 mV
o
No undershoot or overshoot at the start and at the end of transmit slots
o
Voltage ripple during transmit slots must be minimized:
less than 70 mVpp if f
ripple
≤
200 kHz
less than 10 mVpp if 200 kHz < f
ripple
≤
400 kHz
less than 2 mVpp if f
ripple
> 400 kHz
Time
undershoot
overshoot
ripple
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 4: Description of the VCC voltage profile versus time during a GSM call
☞
Any degradation in power supply performance (due to losses, noise or transients) will directly
affect the RF performance of the module since the single external DC power source indirectly
supplies all the digital and analog interfaces, and also directly supplies the RF power amplifier (PA).
