TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 96 of 143
Figure 55 illustrates an alternative application circuit solution in which the cellular module supplies a u-blox 1.8 V
GNSS receiver. The
V_INT
1.8 V regulated supply output of the cellular module can be used as supply source for
a u-blox 1.8 V GNSS receiver (u-blox 6 generation receiver or newer) instead of using an external voltage
regulator, as shown in Figure 54. 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 MOS controlled by
the
GPIO2
pin of the cellular modules by means of a suitable inverting transistor as shown in Figure 55,
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 switch on when
V_INT
output is enabled.
According to the
V_INT
supply output voltage ripple characteristic specified in the
TOBY-L4 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.
u-blox GNSS
1.8 V receiver
TxD1
SDA2
SCL2
VCC
1V8
C1
R3
5
V_INT
R5
R4
TP
T2
T1
R1
R2
1V8
1V8
GNSS data ready
GNSS supply enabled
22
GPIO2
SDA
SCL
GPIO3
55
54
24
TOBY-L4 series
EXTINT0
GPIO4
25
GNSS RTC sharing
Figure 55: Application circuit for connecting TOBY-L4 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 40: Components for connecting TOBY-L4 series modules to u-blox 1.8 V GNSS receivers using V_INT as supply
Custom functions over GPIO pins, to improve the integration with u-blox positioning chips and modules,
will be supported by future firmware versions.