SARA-R5 series - System integration manual
UBX-19041356 - R04 Design-in Page 54 of 118
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2.3.2 Module reset (RESET_N)
2.3.2.1 Guidelines for RESET_N circuit design
SARA-R5 series RESET_N is equipped with an internal active pull-up; an external pull-up resistor is
not required and should not be provided.
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 31 and Table 17.
☞ 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 31.
☞ RESET_N input pin should not be driven high by an external device, as it may cause start up issues.
Table 17: 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
input pin.
2.3.2.2 Guidelines for RESET_N layout design
The RESET_N circuit require careful layout due to the pin function (see section 1.6.3). 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.
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