u-blox LEXI-R422, System Integration Manual

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LEXI-R422 - System integration manual
UBX-23007449 - R02 Design-in Page 79 of 108
C1-Public
Connection with u-blox 3.0 V GNSS receivers
Figure 60 shows an application circuit for connecting the cellular module to an external u-blox 3.0 V
GNSS receiver:
• As the SDA and SCL pins of the cellular module are not tolerant up to 3.0 V, the connection to the
related I2C pins of the u-blox 3.0 V GNSS receiver must be provided using a suitable I2C-bus
bidirectional voltage translator (e.g. TI TCA9406, which additionally provides the partial power
down feature so that the GNSS 3.0 V supply can be ramped up before the
V_INT 1.8 V cellular
supply). External pull-up resistors are not needed on the cellular module side, as they are already
integrated in the cellular module.
• The GPIO2 is connected to the active-high enable pin of the voltage regulator that supplies the
u-blox 3.0 V GNSS receiver providing the “GNSS supply enable” function. A pull -down resistor is
provided to avoid a switch on of the positioning receiver when the cellular module is switched off
or in the reset state.
• The GPIO3 pin is connected to the TxD pin of the u-blox 3.0 V GNSS receiver providing the
additional “GNSS Tx data ready” function, using a suitable unidirectional general purpose voltage
translator (e.g. TI SN74AVC2T245, which additionally provides the partial power down feature so
that the 3.0 V GNSS supply can be also ramped up before the
V_INT 1.8 V cellular supply.
u-blox GNSS
3.0 V receiver
R4
GPIO3
1V8
B1 A1
GND
U3
B2 A2
VCCB VCCA
Unidirectional
voltage translator
C4
C5
3V0
TxD
R1
IN OUT
LDO regulator
SHDNn
R2
VMAIN 3V0
U1
R3
GPIO2
P1
SDA
N1
SCL
1V8
SDA_A SDA_B
GND
U2
SCL_A SCL_B
VCCA VCCB
I2C-bus bidirectional
voltage translator
A11
V_INT
C1
C2 C3
R3
SDA
SCL
VCC
DIR1
DIR2 OEn
OE
GNSS data ready
GNSS supply enable
GND
LEXI-R422
Figure 60: Application circuit for connecting LEXI-R422 modules to u-blox 3.0 V GNSS receivers
Reference Description Part number - Manufacturer
R1, R2 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
C2, C3, C4, C5 100 nF capacitor ceramic X5R 0402 10% 10V GRM155R71C104KA01 - Murata
U1, C1 Voltage regulator for GNSS receiver and related
output bypass capacitor See GNSS receiver hardware integration manual
U2 I2C-bus bidirectional voltage translator TCA9406DCUR - Texas Instruments
U3 Generic unidirectional voltage translator SN74AVC2T245 - Texas Instruments
Table 37: Components for connecting LEXI-R422 modules to u-blox 3.0 V GNSS receivers
☞
For additional guidelines regarding the design of applications with u-blox 3.0 V GNSS receivers,
see the hardware integration manual of the u-blox GNSS receivers.
☞
For additional guidelines regarding celluar and GNSS RF coexistence, see section 2.4.2