LISA-U2 series - System integration manual
UBX-13001118 - R27
System description
Page 89 of 183
C1-Public
Connection with u-blox 1.8 V GNSS receivers
shows an application circuit for connecting a LISA-U2 cellular module to a u-blox 1.8 V GNSS
receiver.
•
The
SDA
and
SCL
pins of the LISA-U2 cellular module are directly connected to the corresponding
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 LISA-U2 cellular module.
•
GPIO3
and
GPIO4
pins are directly connected respectively to the
TxD1
and
EXTINT0
pins of the u-
blox 1.8 V GNSS receiver
to provide “GNSS data ready” and “GNSS RTC sharing” functions.
•
A pull-down resistor is mounted on the
GPIO4
line for correct “GNSS RTC sharing” function
implementation.
•
A pull-down resistor is mounted on the
GPIO2
line to avoid a switch-on of the u-blox GNSS receiver
when the LISA-U2 module is in the internal reset state.
•
The
V_BCKP
supply output of the LISA-U2 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 duration of the GNSS
VCC
outage) and to maintain the configuration settings saved in the backup RAM.
☞
“GNSS data ready” and “GNSS RTC sharing” functions are not supported by all u
-blox GNSS
receivers HW or ROM/FW versions. See the GNSS implementation application note
Hardware Integration Manual of the u-blox GNSS receivers for the supported features.
LISA-U2 series
R1
IN
OUT
GND
GPS LDO
Regulator
SHDN
u-blox GNSS
1.8 V receiver
SDA2
SCL2
R2
1V8 1V8
VMAIN
1V8
U1
21
GPIO2
SDA
SCL
C1
TxD1
EXTINT0
GPIO3
GPIO4
46
45
23
24
VCC
R3
V_BCKP
V_BCKP
2
R4
Figure 47: DDC Application circuit for u-blox 1.8 V GNSS receiver
Reference
Description
Part Number - Manufacturer
R1, R2, R4
4.7 k
Ω
Resistor 0402 5% 0.1 W
RC0402JR-074K7L - Yageo Phycomp
R3
47 k
Ω
Resistor 0402 5% 0.1 W
RC0402JR-0747KL - Yageo Phycomp
U1
Voltage Regulator for GNSS receiver
See GNSS receiver Hardware Integration Manual
Table 38: Components for DDC application circuit for u-blox 1.8 V GNSS receiver