Integration Manual

TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R04 Advance Information Design-in
Page 76 of 141
2.3.2 Module reset (RESET_N or PERST#)
2.3.2.1 Guidelines for RESET_N and PERST# circuit design
The TOBY-L2 series RESET_N is equipped with an internal pull-up to the VCC supply and the MPCI-L2 series
PERST# is equipped with an internal pull-up to the 3.3 V rail, as described in Figure 37. An external pull-up
resistor is not required and should not be provided.
If connecting the RESET_N or PERST# 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 37 and Table 22.
ESD sensitivity rating of the RESET_N and PERST# pins 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 or PERST# 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 and PERST# inputs from an application processor as they
are equipped with an internal pull-up to VCC supply and to the 3.3 V rail respectively, as described in Figure 37.
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-L2 series
VCC
23
RESET_N
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
TOBY-L2 series
VCC
23
RESET_N
TP
TP
50 k
50 k
MPCI-L2 series
22
PERST#
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
MPCI-L2 series
22
PERST#
45 k 45 k
3V3
3V3
Figure 37: RESET_N and PERST# 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 22: Example of ESD protection component for the RESET_N and PERST# 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.