User Manual

LARA-R2 series - System Integration Manual
UBX-16010573 - R02 Objective Specification Design-in
Page 111 of 148
Figure 61 illustrates an alternative solution as 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 60. 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 61, 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 LARA-R2 series Data Sheet [1]:
 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 ‘02’ product version)
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 61: 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 45: 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 to the Hardware Integration Manual of the u-blox GNSS receivers.