User Manual

TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R08 Early Production Information Design-in
Page 83 of 158
If the RTC timing is not required when the VCC supply is removed, it is not needed to connect the
V_BCKP pin to an external capacitor or battery. In this case the date and time are not updated when VCC
is disconnected. If VCC is always supplied, then the internal regulator is supplied from the main supply
and there is no need for an external component on V_BCKP.
Combining a cellular module with a u-blox GNSS positioning receiver, the positioning receiver VCC supply is
controlled by the cellular module by means of the “GNSS supply enable” function provided by the GPIO2 of the
cellular module. In this case the V_BCKP supply output of the cellular module can be connected to the V_BCKP
backup supply input pin of the GNSS receiver to provide the supply for the positioning real time clock and
backup RAM when the VCC supply of the cellular module is within its operating range and the VCC supply of
the GNSS receiver is disabled. This enables the u-blox GNSS receiver to recover from a power breakdown with
either a hot start or a warm start (depending on the duration of the positioning VCC outage) and to maintain
the configuration settings saved in the backup RAM. See section 2.6.3 for more details regarding the application
circuit with a u-blox GNSS receiver.
V_BCKP supply output pin provides internal short circuit protection to limit start-up current and protect the
device in short circuit situations. No additional external short circuit protection is required.
Do not apply loads which might exceed the limit for maximum available current from V_BCKP supply (see
TOBY-L2 series Data Sheet [1]) as this can cause malfunctions in internal circuitry.
ESD sensitivity rating of the V_BCKP supply pin is 1 kV (Human Body Model according to JESD22-A114).
Higher protection level could be required if the line is externally accessible and it can be achieved by
mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor array) close to the accessible point.
2.2.2.2 Guidelines for V_BCKP layout design
V_BCKP supply requires careful layout: avoid injecting noise on this voltage domain as it may affect the stability
of the internal circuitry.