User Manual

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 [1].
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.