SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R08
Objective Specification
System description
Page 29 of 188
1.5.2
RTC supply input/output (V_BCKP)
The
V_BCKP
pin of SARA-G3 and SARA-U2 series 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 15. 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
Power
Management
SARA-G340 / SARA-G350
SARA-U2 series
32 kHz
Baseband
Processor
51
VCC
52
VCC
53
VCC
2
V_BCKP
Linear
LDO
RTC
Power
Management
SARA-G300 / SARA-G310
32 kHz
31
EXT32K
Figure 15: 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 the
SARA-G3 series Data Sheet
[1] and
SARA-U2 series Data Sheet
[2]) 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]). See the
[3] for more details.
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 8.
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
Table 8: RTC value reliability as function of V_BCKP voltage value
Consider that the module cannot switch on if a valid voltage is not present on
VCC
even when the RTC is
supplied through
V_BCKP
(meaning that
VCC
is mandatory to switch on the module).
