TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R07
Advance Information
Design-in
Page 86 of 158
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 42. 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 42 and Table 23.
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 42.
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 42: 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 23: 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.
