Ublox SARA-N4 Series, System Integration Manual

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SARA-R4/N4 series - System Integration Manual
UBX-16029218 - R11 Design-in Page 78 of 157
2.3.2 Module reset (RESET_N)
2.3.2.1 Guidelines for RESET_N circuit design
SARA-R4/N4 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 30 and Table 21 .
☞
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 30 .
☞
RESET_N input pin should not be driven high by an external device, as it may cause start up issues.
SARA-R4/ N4
18 RESET_N
Power-on
push but t on
ESD
Open
Drain
Out put
Applicat ion
Processor
SARA-R4/ N4
18 RESET_N
TP TP
Figure 30: 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 21: 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.