SARA-R4 series - System Integration Manual
UBX-16029218 - R06
Design-in
Page 48 of 102
2.3.2
Module reset (RESET_N)
2.3.2.1
Guidelines for RESET_N circuit design
SARA-R4 series
RESET_N
is equipped with an internal pull-up; an external pull-up resistor is not required.
If connecting the
RESET_N
input to a push button, the pin will be externally accessible on the application device.
According to EMC/ESD requirements of the application, an additional ESD protection device (e.g. the EPCOS
CA05P4S14THSG varistor) should be provided close to accessible point on the line connected to this pin, as
described in Figure 19 and Table 16.
ESD sensitivity rating of the
RESET_N
pin is 1 kV (HBM according to JESD22-A114). Higher protection
level can be required if the line is externally accessible on the application board, e.g. if an accessible push
button is directly connected to the
RESET_N
pin, and it can be achieved by mounting an ESD protection
(e.g. EPCOS CA05P4S14THSG varistor) close to accessible point.
An open drain output or open collector output is suitable to drive the
RESET_N
input from an application
processor, as described in Figure 19.
The
RESET_N
input pin should not be driven high by an external device, as it may cause start up issues.
SARA-R4 series
18
RESET_N
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
SARA-R4 series
18
RESET_N
TP
TP
Figure 19: RESET_N application circuits using a push button and an open drain output of an application processor
Reference
Description
Remarks
ESD
Varistor for ESD protection
CT0402S14AHSG - EPCOS
Table 16: Example of ESD protection component for the RESET_N application circuits
If the external reset function is not required by the customer application, the
RESET_N
input pin can be
left unconnected to external components, but it is recommended providing direct access on the
application board by means of an accessible test point directly connected to the
RESET_N
pin.
2.3.2.2
Guidelines for RESET_N layout design
The
RESET_N
circuit require careful layout due to the pin function: ensure that the voltage level is well defined
during operation and no transient noise is coupled on this line, otherwise the module might detect a spurious
reset request. It is recommended to keep the connection line to
RESET_N
pin as short as possible.
