Ublox TOBY-R2 Series, System Integration Manual, Page: 108 / 151

TOBY-R2 series - System integration manual
UBX-16010572 - R10 Design-in Page 108 of 151
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 I2C 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 I2C 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
VMAIN 1V8
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
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 45: Components for connecting TOBY-R2 series modules to u-blox 1.8 V GNSS receivers