User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R18 Advance Information Design-in
Page 140 of 206
Connection with u-blox 3.0 V GNSS receivers
Figure 80 shows an application circuit example for connecting a SARA-G340 or a SARA-G350 cellular module to
a u-blox 3.0 V GNSS receiver:
x The SDA and SCL pins of SARA-G340 / SARA-G350 are directly connected to the related pins of the u-blox
3.0 V GNSS receiver, with appropriate pull-up resistors connected to the 3.0 V GNSS supply enabled after
the V_INT supply of the I
2
C pins of the cellular module. An I
2
C-bus Voltage Translator is not needed because
the SARA-G340 / SARA-G350 DDC (I
2
C) pins are capable up to 3.3 V.
x The GPIO2 is connected to the active-high enable pin of the voltage regulator that supplies the u-blox 3.0 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.
x As the GPIO3 and GPIO4 pins of SARA-G340 / SARA-G350 cellular modules are not tolerant up to 3.0 V,
the connection to the related pins of the u-blox 3.0 V GNSS receiver must be provided using a proper
Unidirectional General Purpose Voltage Translator (e.g. TI SN74AVC2T245, which additionally provides the
partial power down feature so that the 3.0 V GNSS supply can be also ramped up before the V_INT 1.8 V
cellular supply).
x The V_BCKP supply output of SARA-G340 / SARA-G350 is directly connected to the V_BCKP backup supply
input pin of the u-blox 3.0 V GNSS receiver as in the application circuit for a u-blox 1.8 V GNSS receiver.
SARA-G340 / SARA-G350
R1
INOUT
GND
GNSS LDO
Regulator
SHDN
u-blox GNSS
3.0 V receiver
SDA2
SCL2
R2
3V0
3V0
VMAIN3V0
U1
23
GPIO2
SDA
SCL
C1
26
27
VCC
R3
V_BCKP V_BCKP
2
24
GPIO3
25
GPIO4
1V8
B1 A1
GND
U2
B2A2
VCCBVCCA
Unidirectional
Voltage Translator
C2
C3
3V0
TxD1
EXTINT0
4
V_INT
DIR1
DIR2
OE
GNSS data ready
GNSS RTC sharing
TP
GNSS supply enabled
0 Ω
TP
Figure 80: Application circuit for connecting SARA-G3 modules to u-blox 3.0 V GNSS receivers
Reference Description Part Number – Manufacturer
R1, R2
4.7 kΩ Resistor 0402 5% 0.1 W
RC0402JR-074K7L - Yageo Phycomp
R3
47 kΩ Resistor 0402 5% 0.1 W
RC0402JR-0747KL - Yageo Phycomp
C2, C3
100 nF Capacitor Ceramic X5R 0402 10% 10V
GRM155R71C104KA01 - Murata
U1
Voltage Regulator for GNSS receiver
See GNSS receiver Hardware Integration Manual
U2
Generic Unidirectional Voltage Translator
SN74AVC2T245 - Texas Instruments
Table 51: Components for connecting SARA-G3 modules to u-blox 3.0 V GNSS receivers