Integration Manual
TSD-19090601 - R15 Contents Page 102 of 143
☞ If the pins are not used as DDC (I
2
C) bus interface, they can be left unconnected.
Connection with u-blox 1.8 V GNSS devices
Figure 37 shows an application circuit for connecting the cellular modules to a u-blox 1.8 V GNSS device.
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 device, 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 device implementing the “GNSS supply enable” function, with an
appropriate pull-down resistor mounted on the GPIO2 line to avoid an improper switch-on of the u-
blox GNSS device.
GPIO3 pin is directly connected to the TXD1 pin of the u-blox 1.8 V GNSS device providing “GNSS Tx
data ready” function.
The V_BCKP backup supply input pin of the GNSS device is connected to the external battery 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 device is disabled. This enables the u-blox
GNSS device 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 device
SDA2
SCL2
R2
1V8 1V8
VMAIN
1V8
U1
22
GPIO2
SDA
SCL
C1
TxD1 GPIO3
55
54
24
VCC
R3
GNSS Tx data ready
GNSS supply enabled
TOBY-L3 series
Figure 37: Application circuit for connecting TOBY-L3 series modules to u-blox 1.8 V GNSS devices
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 device and capacitor
See GNSS device Hardware Integration Manual
Table 39: Components for connecting TOBY-L3 series modules to u-blox 1.8 V GNSS devices