TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
System description
Page 30 of 143
1.5.2
RTC back-up supply (V_BCKP)
When the
VCC
module supply input voltage is within the valid operating range, the internal Power Management
Unit (PMU) supplies the Real Time Clock (RTC) through the rail available at the
V_BCKP
pin.
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 the programmable alarm functions available.
If the
VCC
module supply input voltage is under the minimum operating limit (e.g. during the not powered
mode), the RTC can be externally supplied through the
V_BCKP
pin. 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 a very low current consumption, but is highly temperature dependent.
If
V_BCKP
is left unconnected and the module main supply is not applied to the
VCC
pins, the RTC is supplied
from a small bypass capacitor mounted inside the module. However, this small capacitor is not able to provide a
long buffering time: within a few milliseconds the voltage on
V_BCKP
will drop below the valid range. This has
no impact on cellular connectivity, as all the module functionalities do not rely on date and time settings.
1.5.3
Generic digital interfaces supply output (V_INT)
The
V_INT
output pin of the TOBY-L4 series modules is connected to an internal 1.8 V supply. This supply is
internally generated by a switching step-down regulator integrated in the Power Management Unit and it is
internally used to source the generic digital I/O interfaces of the cellular module, as illustrated in Figure 11. The
output of this regulator is enabled when the module is switched on and it is disabled when the module is
switched off.
Baseband
Processor
70
VCC
71
VCC
72
VCC
5
V_INT
Switching
Step-Down
Power
Management
TOBY-L4 series
Digital I/O
Figure 11: TOBY-L4 series generic digital interfaces supply output (V_INT) simplified block diagram
The switching regulator operates in Pulse Width Modulation (PWM) mode for greater efficiency at high output
loads and it automatically switches to Pulse Frequency Modulation (PFM) power save mode for greater efficiency
at low output loads.
