u-blox LARA-R2 series System Integration Manual page 80

Combining a LARA-R2 series 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. Refer to section 2.6.4 for more details
regarding the application circuit with a u-blox GNSS receiver.
The internal regulator for V_BCKP is optimized for low leakage current and very light loads. Do not apply
loads which might exceed the limit for maximum available current from V_BCKP supply, as this can cause
malfunctions in the module. LARA-R2 series Data Sheet [1] describes the detailed electrical characteristics.
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.
ESD sensitivity rating of the V_BCKP supply pin is 1 kV (Human Body Model according to JESD22-A114).
Higher protection level can be required if the line is externally accessible on the application board, e.g. if
an accessible back-up battery connector is directly connected to V_BCKP pin, 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
RTC supply (V_BCKP) requires careful layout: avoid injecting noise on this voltage domain as it may affect the
stability of the 32 kHz oscillator.
UBX-16010573 - R02
LARA-R2 series - System Integration Manual
Objective Specification Design-in
Page 80 of 148