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SARA-G3 series - System Integration Manual
UBX-13000995 - R06 Objective Specification System description
Page 36 of 218
1.5.2 RTC supply input/output (V_BCKP)
The V_BCKP pin of SARA-G3 modules connects the supply for the Real Time Clock (RTC) and Power-
On internal logic. This supply domain is internally generated by a linear LDO regulator integrated in the
Power Management Unit, as described in
Figure 11Figure 11 . The output of this linear regulator is always
enabled when the main voltage supply provided to the module through the VCC pins is within the valid
operating range, with the module switched off or switched on.
Baseband
Processor
51 VCC
52
VCC
53
VCC
2 V_BCKP
Linear
LDO
RTC
Pow er
M anagement
SARA-G350
32 kHz
Baseband
Processor
51 VCC
52
VCC
53
VCC
2 V_BCKP
Linear
LDO
RTC
Pow er
M anagement
SARA-G300 / SARA-G310
32 kHz
31 EXT32K
Figure 11: SARA-G3 series RTC supply input/output (V_BCKP) and 32 kHz RTC timing reference clock simplified block diagram
The RTC provides the module time reference (date and time) that is used to set the wake-up interval
during the idle-mode periods between network paging, and is able to make available the programmable
alarm functions.
The RTC functions are available also in power-down mode when the
V_BCKP voltage is within its valid
range (specified in the “Input characteristics of Supply/Power pins” table in
SARA-G3 series Data
Sheet [1]) and, for SARA-G300 / SARA-G310 modules only, when their
EXT32K input pin is fed by
an external 32.768 kHz signal with proper characteristics (specified in the “EXT32K pin characteristics”
table in
SARA-G3 series Data Sheet [1]).
The RTC can be supplied from an external back-up battery through the V_BCKP , when the main voltage
supply is not provided to the module through VCC . This lets the time reference (date and time) run until
the V_BCKP voltage is within its valid range, even when the main supply is not provided to the module.
The RTC oscillator does not necessarily stop operation (i.e. the RTC counting does not necessarily stop)
when
V_BCKP voltage value drops below the specified operating range minimum limit (1.00 V): the RTC
value read after a system restart could be not reliable, as explained in Table 7Table 7 .
V_BCKP voltage value RTC value reliability Notes
1.00 V < V_BCKP < 2.40 V RTC oscillator does not stop operation
RTC value read after a restart of the system is reliable V_BCKP within operating range
0.05 V < V_BCKP < 1.00 V RTC oscillator does not necessarily stop operation
RTC value read after a restart of the system is not
reliable V_BCKP below operating range
0.00 V < V_BCKP < 0.05 V RTC oscillator stops operation
RTC value read after a restart of the system is reliable V_BCKP below operating range