SARA-G450 - System integration manual
UBX-18046432 - R08
Design-in
Page 99 of 143
C1-Public
4
V_INT
TxD
Application Processor
(3.0V DTE)
RxD
GND
SARA-G450
(1.8V DCE)
17
TXD_AUX
19
RXD_AUX
GND
1V8
B1
A1
GND
U1
VCCB
VCCA
Unidirectional
voltage translator
C1
C2
3V0
DIR1
DIR2
OE
VCC
B2
A2
TP
21
VSEL
Figure 61: AUX UART application circuit (3.0 V DTE / 1.8 V DCE)
Reference
Description
Part number – Manufacturer
C1, C2
100 nF capacitor ceramic X7R 0402 10% 16 V
GRM155R61A104KA01 – Murata
U1
Unidirectional voltage translator
SN74AVC2T245
18
- Texas Instruments
Table 36: Parts for AUX UART application circuit (3.0 V DTE / 1.8 V DCE)
2.6.2.2
Guidelines for AUX UART layout design
The AUX UART serial interface requires the same consideration regarding electromagnetic
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.
2.6.3
Additional serial interface for FW upgrade and Tracing (FT UART)
2.6.3.1
Guidelines for FT UART circuit design
It is not necessary to connect this interface to the application processor, but it is highly recommended
to provide on the application board a directly accessible Test-Point for the TXD_FT and RXD_FT pins
of the module for execution of firmware upgrades and for diagnostic purposes: provide a Test-Point
on each line to accommodate the access and leave these lines detached from any other device, as
described in
scaling
SARA-G450
29
TXD_FT
28
RXD_FT
TP
TP
Figure 62: FT UART interface application circuit
☞
The ESD sensitivity rating of additional FT UART pins is 1 kV (Human Body Model according to
JESD22-A114). A higher protection level could be required if the lines are externally accessible on
the application board. This higher protection level can be achieved by mounting an ESD protection
(e.g. EPCOS CA05P4S14THSG varistor array) close to accessible points.
18
Voltage translator providing partial power-down feature so that the DTE 3.0 V supply can be also ramped up before V_INT
1.8 V supply