SARA-R4 series - System Integration Manual
UBX-16029218 - R06
Design-in
Page 47 of 102
2.3
System functions interfaces
2.3.1
Module power-on (PWR_ON)
2.3.1.1
Guidelines for PWR_ON circuit design
SARA-R4 series
PWR_ON
input is equipped with an internal active pull-up resistor; an external pull-up resistor is
not required and should not be provided.
If connecting the
PWR_ON
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 should be provided
close to the accessible point, as described in Figure 18 and Table 15.
ESD sensitivity rating of the
PWR_ON
pin is 1 kV (Human Body Model 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
PWR_ON
pin, and it can be achieved by mounting an ESD
protection (e.g. EPCOS CA05P4S14THSG varistor) close to the accessible point.
An open drain or open collector output is suitable to drive the
PWR_ON
input from an application processor, as
described in Figure 18.
The
PWR_ON
input pin should not be driven high by an external device, as it may cause start up issues.
SARA-R4 series
15
PWR_ON
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
SARA-R4 series
15
PWR_ON
TP
TP
Figure 18: PWR_ON application circuits using a push button and an open drain output of an application processor
Reference
Description
Remarks
ESD
CT0402S14AHSG - EPCOS
Varistor array for ESD protection
Table 15: Example ESD protection component for the PWR_ON application circuit
It is recommended to provide direct access to the
PWR_ON
pin on the application board by means of an
accessible test point directly connected to the
PWR_ON
pin.
2.3.1.2
Guidelines for PWR_ON layout design
The power-on circuit (
PWR_ON
) requires careful layout since it is the sensitive input available to switch on and
switch off the SARA-R4 series modules. It is required to 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 power-on
request.
