SARA-G450 - System integration manual
UBX-18046432 - R08 Design-in Page 101 of 143
C1-Public
Connection with u-blox 1.8 V GNSS receivers
Figure 63 shows an application circuit example for connecting a SARA-G450 cellular module to a
u-blox 1.8 V GNSS receiver:
The VSEL pin is connected to GND so that SARA-G450 module’s generic digital interfaces are
configured to operate at 1.8 V (V_INT = 1.8 V, if VSEL pin is connected to GND; see 1.5.3).
The SDA and SCL pins of the cellular module are directly connected to the related pins of the u-blox
1.8 V GNSS receiver, with appropriate pull-up resistors connected to the 1.8 V GNSS supply enabled
after the V_INT supply of the I2C pins of the cellular module.
The GPIO2 pin is connected to the active-high enable pin of the voltage regulator that supplies the
u-blox 1.8 V GNSS receiver providing the “GNSS supply enable” function. A pull-down resistor is
provided to avoid a switch-on of the positioning receiver when the cellular module is switched off
or in the reset state.
The V_BCKP supply output of the cellular module is connected to the V_BCKP 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 actual duration of the GNSS VCC outage) and
to maintain the configuration settings saved in the backup RAM.
SARA-G450
(1.8 V)
R1
INOUT
GND
GNSS LDO
regulator
SHDN
u-blox GNSS
1.8 V receiver
SDA2
SCL2
R2
1V8 1V8
VMAIN1V8
U1
23
GPIO2
SDA
SCL
C1
26
27
VCC
R3
V_BCKP V_BCKP
2
GNSS supply enable
21 VSEL
Figure 63: Application circuit for connecting SARA-G450 (1.8 V) modules to u-blox 1.8 V GNSS receivers
Part number - Manufacturer
4.7 kΩ resistor 0402 5% 0.1 W
RC0402JR-074K7L - Yageo Phycomp
47 kΩ resistor 0402 5% 0.1 W
RC0402JR-0747KL - Yageo Phycomp
Voltage regulator for GNSS receiver and related
output bypass capacitor
See GNSS receiver hardware integration manual
Table 37: Components for connecting SARA-G450 (1.8 V) modules to u-blox 1.8 V GNSS receivers
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