Ublox SARA-G450 Series, System Integration Manual

Page: 21 / 143

SARA-G450 - System integration manual
UBX-18046432 - R08 System description Page 21 of 143
C1-Public
1.5.2 RTC supply input/output (V_BCKP)
The V_BCKP pin of SARA-G450 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 10 . 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
Unit
SARA-G450
32 kHz
Figure 10: RTC supply input/output (V_BCKP) and 32 kHz 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 not-powered mode when the V_BCKP is within its valid range
(specified in the “Input characteristics of Supply/Power pins” table in the SARA-G450 data sheet
[1] ).
See the u-blox AT commands manual [11] 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 the V_BCKP voltage value drops below the specified operating range minimum limit, but
the RTC value read after a system restart may not be reliable.
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).
If V_BCKP is left unconnected and the module main voltage supply is removed from VCC, the RTC is
supplied from the bypass capacitor mounted inside the module. However, this capacitor is not able to
provide a long buffering time: within a few milliseconds, the voltage on V_BCKP will go below the valid
range. This has no impact on cellular connectivity, as none of the module functionalities rely on date
and time setting.