TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 69 of 143
2.3.2
Module reset (RESET_N)
2.3.2.1
Guidelines for RESET_N circuit design
TOBY-L4 series
RESET_N
line is equipped with an internal pull-up to the
V_INT
supply as illustrated in Figure 31.
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 the EMC/ESD requirements of the application, an additional ESD protection device (e.g. the EPCOS
CA05P4S14THSG varistor) should be provided close to the accessible point on the line connected to this pin, as
illustrated in Figure 31 and Table 23.
The ESD sensitivity rating of the
RESET_N
pin is 1 kV (HBM according to JESD22-A114). A 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 the 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_INT
supply, as illustrated in Figure 31.
A compatible push-pull output of an application processor can also be used. In any case, take care to set the
correct level in all the possible scenarios to avoid an inappropriate module reset.
TOBY-L4 series
5
V_INT
23
RESET_N
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
TOBY-L4 series
5
V_INT
23
RESET_N
TP
TP
100 k
100 k
Figure 31: 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 23: 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 to provide 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 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 the
RESET_N
pin as short as possible.
