User's Manual

SARA-G3 and SARA-U2 series - System Integration Manual
UBX-13000995 - R18 Advance Information Design-in
Page 139 of 206
The supply of the u-blox 1.8 V GNSS receiver can be switched off using an external p-channel MOSFET
controlled by the GPIO2 pin by means of a proper inverting transistor as shown in Figure 79, implementing the
“GNSS supply enable” function. If this feature is not required, the V_INT supply output can be directly
connected to the u-blox 1.8 V GNSS receiver, so that it will be switched on when V_INT output is enabled.
The V_INT supply output provides low voltage ripple (up to 15 mVpp) when the module is in active-mode or in
connected-mode, but it provides higher voltage ripple (up to 90 mVpp on SARA-G3 series, or up to 70 mVpp on
SARA-U2 series) when the module is in the low power idle-mode with power saving configuration enabled by
the AT+UPSV (see u-blox AT Commands Manual [3]).
According to the voltage ripple characteristic of the V_INT supply output:
x The power saving configuration cannot be enabled to use V_INT output to properly supply any 1.8 V GNSS
receiver of the u-blox 6 generation and any 1.8 V GNSS receiver of the u-blox 7 generation or any newer
u-blox GNSS receiver generation with TCXO.
x The power saving configuration can be enabled to use V_INT output to properly supply any 1.8 V GNSS
receiver of the u-blox 7 generation or any newer u-blox GNSS receiver generation without TCXO.
x Additional filtering may be needed to properly supply an external LNA, depending on the characteristics of
the used LNA, adding a series ferrite bead and a bypass capacitor (e.g. the Murata BLM15HD182SN1 ferrite
bead and the Murata GRM1555C1H220J 22 pF capacitor) at the input of the external LNA supply line.
SARA-G340 / SARA-G350
SARA-U2 series
u-blox GNSS
1.8 V receiver
TxD1
EXTINT0
GPIO3
GPIO4
24
25
V_BCKP V_BCKP
2
SDA2
SCL2
23
GPIO2
SDA
SCL
26
27
VCC
1V8
C1
R3
4
V_INT
R5
R4
TP
T2
T1
R1 R2
1V8
1V8
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 using V_INT as supply
Reference Description Part Number - Manufacturer
R1, R2
4.7 k: Resistor 0402 5% 0.1 W
RC0402JR-074K7L - Yageo Phycomp
R3
47 k: Resistor 0402 5% 0.1 W
RC0402JR-0747KL - Yageo Phycomp
R4
10 k: Resistor 0402 5% 0.1 W
RC0402JR-0710KL - Yageo Phycomp
R5
100 k: Resistor 0402 5% 0.1 W
RC0402JR-07100KL - Yageo Phycomp
T1
P-Channel MOSFET Low On-Resistance
IRLML6401 - International Rectifier or NTZS3151P - ON Semi
T2
NPN BJT Transistor
BC847 - Infineon
C1
100 nF Capacitor Ceramic X7R 0402 10% 16 V
GRM155R71C104KA01 - Murata
Table 50: Components for connecting SARA-G3 / SARA-U2 modules to u-blox 1.8 V GNSS receivers using V_INT as supply
For additional guidelines regarding the design of applications with u-blox 1.8 V GNSS receivers see the GNSS
Implementation Application Note [27] and to the Hardware Integration Manual of the u-blox GNSS receivers.