Integration Manual
SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R13 Design-in Page 80 of 119
Connection with u-blox 1.8 V GNSS receivers
Figure 51 shows an application circuit for connecting the cellular module to a u-blox 1.8 V GNSS receiver:
• The SDA and SCL pins of the cellular module are directly connected to the related pins of the u-blox 1.8 V GNSS
receiver. External pull-up resistors are not needed, as they are already integrated in the cellular module.
• The GPIO2 pin is connected to the active-high enable pin of the voltage regulator that supplies the u-blox 1.8 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 TXD1 pin of the u-blox 1.8 V GNSS receiver providing the additional “GNSS Tx data
ready” function.
IN
OUT
GND
GNSS LDO
Regulat or
SHDN
u-blox GNSS
1.8 V receiver
SDA2
SCL2
VMAIN1V8
U1
23
GPIO2
SDA
SCL
C1
26
27
VCC
R1
GNSS supp ly enabled
SARA-R4 / N4
(except ’0 0’,’0 1’ versions)
TxD1
GPIO3
24
GNSS dat a ready
Figure 51: Application circuit for connecting SARA-R4/N4 series modules to u-blox 1.8 V GNSS receivers
Reference Description Part Number - Manufacturer
R1 47 kΩ Resistor 0402 5% 0.1 W RC0402JR-0747KL - Yageo Phycomp
U1 Voltage Regulator for GNSS receiver See GNSS receiver Hardware Integration Manual
Table 34: Components for connecting SARA-R4/N4 series modules to u-blox 1.8 V GNSS receivers
For additional guidelines regarding the design of applications with u-blox 1.8 V GNSS receivers, see the Hardware
Integration Manual of the u-blox GNSS receivers.
Connection with u-blox 3.0 V GNSS receivers
Figure 52 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 I
2
C pins of
the u-blox 3.0 V GNSS receiver must be provided using a suitable I
2
C-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 TXD1 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.