User's Manual
TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 Design-in
Page 109 of 147
Connection with u-blox 1.8 V GNSS receivers
Figure 61 shows an application circuit for connecting the cellular modules to a u-blox 1.8 V GNSS receiver.
SDA / SCL pins of the cellular module are directly connected to the relative I
2
C pins of the u-blox 1.8 V GNSS
receiver, with appropriate pull-up resistors connected to the 1.8 V GNSS supply enabled after the V_INT
supply of the I
2
C pins of the cellular module.
GPIO2 pin is connected to the shutdown input pin (SHDNn) of the LDO regulators providing the 1.8 V
supply rail for the u-blox 1.8 V GNSS receiver implementing the “GNSS enable” function, with appropriate
pull-down resistor mounted on GPIO2 line to avoid an improper switch on of the u-blox GNSS receiver.
GPIO3 and GPIO4 pins are directly connected respectively to TXD1 and EXTINT0 pins of the u-blox 1.8 V
GNSS receiver providing “GNSS Tx data ready” and “GNSS RTC sharing” functions.
The V_BCKP supply output of the cellular module is connected to the V_BCKP backup supply input pin of
the GNSS receiver to provide the supply for the GNSS real time clock and backup RAM when the VCC supply
of the cellular module is within its operating range and the VCC supply of the GNSS receiver is disabled. This
enables the u-blox GNSS receiver to recover from a power breakdown with either a hot start or a warm start
(depending on the actual duration of the GNSS VCC outage) and to maintain the configuration settings
saved in the backup RAM.
R1
IN
OUT
GND
GNSS LDO
Regulator
SHDNn
u-blox GNSS
1.8 V receiver
SDA2
SCL2
R2
1V8 1V8
VMAIN1V8
U1
22
GPIO2
SDA
SCL
C1
TxD1 GPIO3
55
54
24
VCC
R3
V_BCKP V_BCKP
3
GNSS Tx data ready
GNSS supply enabled
TOBY-R2 series
(except ‘02’ product versions)
EXTINT0 GPIO4
25
GNSS RTC sharing
Figure 61: Application circuit for connecting TOBY-R2 series modules to u-blox 1.8 V GNSS receivers
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
U1, C1
Voltage Regulator for GNSS receiver and capacitor
See GNSS receiver Hardware Integration Manual
Table 44: Components for connecting TOBY-R2 series modules to u-blox 1.8 V GNSS receivers