u-blox LARA-R203 System Integration Manual page 115

Connection with u-blox 3.0 V GNSS receivers
Figure 64 shows an application circuit for connecting the cellular module to a 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
2
I C pins of the u-blox 3.0 V GNSS receiver must be provided using a proper I
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), with proper pull-up resistors.

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.

As the GPIO3 and GPIO4 pins of the cellular module are not tolerant up to 3.0 V, the connection to the
related pins of the u-blox 3.0 V GNSS receiver must be provided using a proper 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).

The V_BCKP supply output of the cellular module can be directly connected to the V_BCKP backup supply
input pin of the GNSS receiver as in the application circuit for a u-blox 1.8 V GNSS receiver.
u-blox GNSS
3.0 V receiver
V_BCKP
VCC
SDA2
SCL2
TxD1
EXTINT0
Figure 64: Application circuit for connecting LARA-R2 series modules to u-blox 3.0 V GNSS receivers
Reference Description
R1, R2, R4, R5 4.7 kΩ Resistor 0402 5% 0.1 W
R3 47 kΩ Resistor 0402 5% 0.1 W
C2, C3, C4, C5 100 nF Capacitor Ceramic X5R 0402 10% 10V
U1, C1 Voltage Regulator for GNSS receiver and related
output bypass capacitor
U2 I2C-bus Bidirectional Voltage Translator
U3 Generic Unidirectional Voltage Translator
Table 47: Components for connecting LARA-R2 series 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 GNSS
Implementation Application Note [22] and the Hardware Integration Manual of the u-blox GNSS receivers.
2.6.4.2 Guidelines for DDC (I
2
The DDC (I C) serial interface requires the same considerations regarding electro-magnetic interference as any
other digital interface. Keep the traces short and avoid coupling with RF line or sensitive analog inputs, since the
signals can cause the radiation of some harmonics of the digital data frequency.
UBX-16010573 - R12
3V0 VMAIN
GNSS LDO Regulator
OUT IN
GND SHDNn
C1
U1
I2C-bus Bidirectional
Voltage Translator
VCCB VCCA
C2
OE
R1 R2
SDA_B SDA_A
SCL_B SCL_A
GND
U2
Unidirectional
3V0 Voltage Translator 1V8
VCCA VCCB
C4
DIR1
A1 B1
A2 B2
DIR2 OEn
GND
U3
2 C) layout design
LARA-R2 series - System Integration Manual
LARA-R2 series
(except LARA-R204-02B-00 and
LARA-R211-02B-00)
V_BCKP
2
GNSS supply enabled
GPIO2
23
R3
1V8
4 V_INT
C3
R4 R5
26 SDA
SCL
27
C5
GNSS data ready
GPIO3
24
GNSS RTC sharing
GPIO4
25
Part Number - Manufacturer
RC0402JR-074K7L - Yageo Phycomp
RC0402JR-0747KL - Yageo Phycomp
GRM155R71C104KA01 - Murata
See GNSS receiver Hardware Integration Manual
TCA9406DCUR - Texas Instruments
SN74AVC2T245 - Texas Instruments
2
C-bus Bidirectional Voltage
Design-in
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