User's Manual

TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 System description
Page 26 of 147
1.5.2 RTC supply input/output (V_BCKP)
The V_BCKP pin of TOBY-R2 series modules connects the supply for the Real Time Clock (RTC). A linear LDO
regulator integrated in the Power Management Unit internally generates this supply, as shown in Figure 11, with
low current capability (see the TOBY-R2 series Data Sheet [1]). The output of this regulator is always enabled
when the main module voltage supply applied to the VCC pins is within the valid operating range.
Baseband
Processor
70
VCC
71
VCC
72
VCC
3
V_BCKP
Linear
LDO
Power
Management
TOBY-R2 series
32 kHz
RTC
Figure 11: TOBY-R2 series RTC supply (V_BCKP) 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 TOBY-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 TOBY-R2 series Data Sheet [1].
If V_BCKP is left unconnected and the module main supply is not applied to the VCC pins, 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.