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TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R07
Advance 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.