Ublox TOBY-L2 series, Руководство по системной интеграции

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TOBY-L2 and MPCI-L2 series - System Integration Manual
UBX-13004618 - R28 Design-in Page 84 of 164
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 43 . 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 43 and Table 24 .
☞
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 43 .
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 43: RESET_N and PERST# application circuits using a push button and an open drain output of an application
processor
Reference Description Part Number – Manufacturer
ESD Varistor for ESD protection CT0402S14AHSG – EPCOS
Table 24: 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 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.