SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R26 Design-in
Page 145 of 217
Connection with u-blox 1.8 V GNSS receivers
Figure 79 shows an application circuit example for connecting a SARA-G340, SARA-G350 or SARA-U2 cellular
module to a u-blox 1.8 V GNSS receiver:
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 I
2
C 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 GPIO3 and GPIO4 pins are directly connected respectively to TXD1 and EXTINT0 pins of the u-blox
1.8 V GNSS receiver providing “GNSS data ready” and “GNSS RTC sharing” functions.
The V_BCKP supply output of the cellular module is 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 actual duration of the GNSS VCC outage) and to maintain the configuration settings
saved in the backup RAM.
SARA-G340 / SARA-G350
SARA-U2 series
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
TxD1
EXTINT0
GPIO3
GPIO4
26
27
24
25
VCC
R3
V_BCKP V_BCKP
2
GNSS data ready
GNSS RTC sharing
GNSS supply enabled
0 Ω
TP
Figure 79: Application circuit for connecting SARA-G3 / SARA-U2 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
See GNSS receiver Hardware Integration Manual
Table 50: Components for connecting SARA-G3 / SARA-U2 modules to u-blox 1.8 V GNSS receivers
Figure 80 illustrates an alternative solution as supply for u-blox 1.8 V GNSS receivers: the V_INT 1.8 V regulated
supply output of SARA-G340 / SARA-G350 / SARA-U2 cellular modules can be used to supply a u-blox 1.8 V
GNSS receiver of the u-blox 6 generation (or any newer u-blox GNSS receiver generation) instead of using an
external voltage regulator as shown in the previous Figure 79. The V_INT supply is able to support the maximum
current consumption of these positioning receivers.
The internal switching step-down regulator that generates the V_INT supply is set to 1.8 V (typical) when the
cellular module is switched on and it is disabled when the module is switched off.
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