LARA-R2 series - System Integration Manual
UBX-16010573 - R02
Objective Specification
System description
Page 25 of 148
1.5.2
RTC supply input/output (V_BCKP)
The
V_BCKP
pin of LARA-R2 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 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
LARA-R2 series
32 kHz
Figure 10: 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
low power idle-mode periods, 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
LARA-R2 series
Data Sheet
[1]). The RTC
can be supplied from an external back-up battery through the
V_BCKP
, when the main module voltage supply is
not applied to the
VCC
pins. 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.
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).
The RTC has very low current consumption, but is highly temperature dependent. For example,
V_BCKP
current
consumption at the maximum operating temperature can be higher than the typical value at 25 °C specified in
the “Input characteristics of Supply/Power pins” table in the
LARA-R2 series Data Sheet
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 few milliseconds the voltage on
V_BCKP
will go below the valid range. This has no impact
on cellular connectivity, as all the module functionalities do not rely on date and time setting.
