LARA-R2 series - System Integration Manual
UBX-16010573 - R02
Objective Specification
Design-in
Page 83 of 148
2.3.2
Module reset (RESET_N)
2.3.2.1
Guidelines for RESET_N circuit design
LARA-R2 series
RESET_N
is equipped with an internal pull-up to the
V_BCKP
supply as described in Figure 38.
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 38 and Table 30.
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.
An open drain output is suitable to drive the
RESET_N
input from an application processor as it is equipped with
an internal pull-up to
V_BCKP
supply, as described in Figure 38.
A compatible push-pull output of an application processor can also be used. In any case, take care to set the
proper level in all the possible scenarios to avoid an inappropriate module reset, switch-on or switch-off.
LARA-R2 series
2
V_BCKP
18
RESET_N
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
LARA-R2 series
2
V_BCKP
18
RESET_N
TP
TP
10 k
10 k
Figure 38: 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 30: 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 directly connected to the
RESET_N
pin.
2.3.2.2
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.
