LARA-R2 series - System Integration Manual
UBX-16010573 - R12
Design-in
Page 114 of 157
Figure 63 illustrates an alternative solution as a supply for u-blox 1.8 V GNSS receivers: the
V_INT
1.8 V regulated
supply output of the cellular module 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 62. 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.
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 63, 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.
According to the
V_INT
supply output voltage ripple characteristic specified in the
LARA-R2 series
Data Sheet
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.
LARA-R2 series
(except LARA-R204-02B-00 and
LARA-R211-02B-00)
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
Figure 63: Application circuit for connecting LARA-R2 series 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 46: Components for connecting LARA-R2 series 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
[22] and the
Hardware Integration Manual
of the u-blox GNSS receivers.
