LISA-U2 series - System integration manual
UBX-13001118 - R27
System description
Page 35 of 183
C1-Public
(specified in the input characteristics of the supply/power pins table in the LISA-U2 series data
sheet
). The connection of the battery to
V_BCKP
should be done with a suitable series resistor for
a rechargeable battery, or with an appropriate series diode for a non-rechargeable battery. The
purpose of the series resistor is to limit the battery charging current due to the battery specifications,
and also to allow a fast rise time of the voltage value at the
V_BCKP
pin after the
VCC
supply has been
provided. The purpose of the series diode is to avoid a current flow from the module
V_BCKP
pin to
the non-rechargeable battery.
Combining a LISA-U2 series cellular module with a u-blox GNSS receiver, the
VCC
supply of the GNSS
receiver 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 LISA-U2 series
cellular module can be connected to the
V_BCKP
backup supply input pin of the GNSS receiver to
provide the supply for the GNSS 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 GNSS
VCC
outage) and to maintain the configuration settings
saved in the backup RAM. See the section
for more details regarding the application circuit with
a u-blox GNSS receiver.
