LENA-R8 series - System integration manual
UBX-22015376 - R02
Design-in
Page 81 of 116
C1-Public
provide two examples of coplanar waveguide designs with differential
characteristic impedance close to 90
and common mode characteristic impedance close to 30
.
The first transmission line can be implemented for a 4-layer PCB stack-up herein described, the
second transmission line can be implemented for a 2-layer PCB stack-up herein described.
35
µ
m
35
µ
m
35
µ
m
35
µ
m
270
µ
m
270
µ
m
760
µ
m
L1 Copper
L3 Copper
L2 Copper
L4 Copper
FR-4 dielectric
FR-4 dielectric
FR-4 dielectric
350
µ
m 400
µ
m
400
µ
m
350
µ
m
400
µ
m
Figure 60: Example of USB line design, with Z
0
close to 90
and Z
CM
close to 30
, for the described 4-layer board layup
35
µ
m
35
µ
m
1510
µ
m
L2 Copper
L1 Copper
FR-4 dielectric
740
µ
m 410
µ
m
410
µ
m
740
µ
m
410
µ
m
Figure 61: Example of USB line design, with Z0 close to 90
and ZCM close to 30
, for the described 2-layer board layup
2.6.3
Cellular I2C interface
2.6.3.1
Guidelines for I2C circuit design
General considerations
The I2C-bus interface can be used to communicate with external u-blox GNSS receivers (LENA-R8001
modules only) and other external I2C-bus devices as an audio codec. Beside the general considerations
explained below, see:
•
the following parts of this section
for guidelines to connect external u-blox GNSS receivers
to the LENA-R8001 modules.
•
the section
for an application circuit example with an external audio codec I2C-bus device.
The
SDA
and
SCL
pins of the module are open drain output as per I2C bus specifications
, and
they have internal active pull-ups to the
V_INT
1.8 V supply rail, so that external pull-up resistors are
not strictly required, but they can be provided to increase the strength and improve signal integrity.
☞
Capacitance and series resistance must be limited on the bus to match the I2C specifications
(maximum proper rise time for
SCL
/
SDA
lines is 1.0
µ
s): route connections as short as possible.
☞
Do not apply voltage to any UART interface pin before the switch-on of the UART supply source
(
V_INT
), to avoid latch-up of circuits and allow a proper boot of the module.
☞
The ESD sensitivity rating of the I2C pins is 1 kV (HBM as per JESD22-A114). Higher protection
level could be required if the lines are externally accessible and it can be achieved by mounting an
ESD protection (e.g. EPCOS CA05P4S14THSG varistor array) close to accessible points.
☞
If the pins are not used as I2C bus interface, they can be left unconnected.
