Ublox SARA-N210, System Integration Manual

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SARA-N2 series - System Integration Manual
UBX-17005143 - R06 Design-in Page 32 of 82
2.3 System functions interfaces
2.3.1 Module reset (RESET_N)
2.3.1.1 Guidelines for RESET_N circuit design
As described in SARA-N2 series Data Sheet [1] , the module has an internal pull-up resistor on the reset
input line, so an external pull-up is not required on the application board.
When the RESET_N input is connected to a push button that shorts the RESET_N pin to ground, the
pin will be externally accessible on the application device. According to EMC/ESD requirements of the
application, provide an additional ESD protection (e.g. EPCOS CA05P4S14THSG varistor array) on the
line connected to this pin, close to accessible point, as described in
Figure 14 and Table 14 .
☞
ESD sensitivity rating of the RESET_N pin is 1 kV (Human Body Model 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 RESET_N pin. Higher protection level can
be achieved by mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor array) close to
accessible point.
When the RESET_N input is connected to an external device (e.g. application processor), an open drain
output can be directly connected without any external pull-up, as described in
Figure 14 and Table 14 .
The internal pull-up resistor provided by the module pulls the line to the high logic level when the
application processor does not force the RESET_N pin low. A compatible push-pull output of an
application processor can be used too.
1:1 scaling
SARA-N2 series
18
RESET_N
Reset
push button
ESD
Open
Drain
Output
Application
Processor
SARA-N2 series
18
RESET_N
TP TP
~78k
VCC
~78k
VCC
Figure 14: 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 14: Example of ESD protection component for the RESET_N application circuit
☞
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 accessible testpoint for diagnostic purpose.
2.3.1.2 Guidelines for RESET_N layout design
The reset circuit (RESET_N) requires 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 as short as possible.