TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 97 of 143
Connection with u-blox 3.0 V GNSS receivers
Figure 56 shows an application circuit for connecting the cellular modules 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 with appropriate pull-up resistors (e.g. the TI TCA9406 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).
GPIO2
pin is connected to the shutdown input pin (
SHDNn
) of the LDO regulators providing the 3.0 V
supply rail for the u-blox 3.0 V GNSS receiver implementing the “GNSS enable” function, with an
appropriate pull-down resistor mounted on the
GPIO2
line to avoid an improper switch-on of the u-blox
GNSS receiver.
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 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
24
GPIO3
1V8
B1
A1
GND
U3
B2
A2
VCCB
VCCA
Unidirectional
Voltage Translator
C4
C5
3V0
TxD1
R1
IN
OUT
GNSS LDO Regulator
SHDNn
R2
VMAIN
3V0
U1
22
GPIO2
55
SDA
54
SCL
R4
R5
1V8
SDA_A
SDA_B
GND
U2
SCL_A
SCL_B
VCCA
VCCB
I2C-bus Bidirectional
Voltage Translator
5
V_INT
C1
C2
C3
R3
SDA2
SCL2
VCC
DIR1
DIR2
OEn
OE
GNSS data ready
GNSS supply enabled
GND
TOBY-L4 series
EXTINT0
GPIO4
25
GNSS RTC sharing
Figure 56: Application circuit for connecting TOBY-L4 series modules to u-blox 3.0 V GNSS receivers
Reference
Description
Part Number - Manufacturer
R1, R2, R4, R5
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
C2, C3, C4, C5
100 nF Capacitor Ceramic X5R 0402 10% 10V
GRM155R71C104KA01 - Murata
U1, C1
Voltage Regulator for GNSS receiver and 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 41: Components for connecting TOBY-L4 series modules to u-blox 3.0 V GNSS receivers
Custom functions over GPIO pins, to improve the integration with u-blox positioning chips and modules,
will be supported by future firmware versions.
2.6.4.2
Guidelines for DDC (I
2
C) layout design
The DDC (I
2
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.
