User's Manual

TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 Design-in
Page 84 of 147
2.3.2 Module reset (RESET_N)
2.3.2.1 Guidelines for RESET_N circuit design
TOBY-R2 series RESET_N is equipped with an internal pull-up to the V_BCKP supply as described in Figure 40.
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 40 and Table 30.
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 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 40.
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.
TOBY-R2 series
3
V_BCKP
23
RESET_N
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
TOBY-R2 series
3
V_BCKP
23
RESET_N
TP
TP
10 k
10 k
Figure 40: 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 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.