SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R08
Objective Specification
Design-in
Page 124 of 188
Connection with u-blox 1.8 V GNSS receivers
Figure 71 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
IN
OUT
GND
GNSS LDO
Regulator
SHDN
u-blox GNSS
1.8 V receiver
SDA2
SCL2
R2
1V8
1V8
VMAIN
1V8
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
Figure 71: Application circuit for connecting SARA-G3 / SARA-U2 modules to u-blox 1.8 V GNSS receivers
Reference
Description
Part Number - Manufacturer
R1, R2
4.7 k
Ω
Resistor 0402 5% 0.1 W
RC0402JR-074K7L - Yageo Phycomp
R3
47 k
Ω
Resistor 0402 5% 0.1 W
RC0402JR-0747KL - Yageo Phycomp
U1
Voltage Regulator for GNSS receiver
See GNSS receiver Hardware Integration Manual
Table 37: Components for connecting SARA-G3 / SARA-U2 modules to u-blox 1.8 V GNSS receivers
Figure 72 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 family (or later u-blox family) instead of using an external voltage regulator as
shown in the previous Figure 71. The
V_INT
supply is able to withstand 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.
