TOBY-L4 series - System Integration Manual
UBX-16024839 - R04
Design-in
Page 68 of 143
2.3
System functions interfaces
2.3.1
Module power-on (PWR_ON)
2.3.1.1
Guidelines for PWR_ON circuit design
TOBY-L4 series
PWR_ON
input is equipped with an internal active pull-up resistor to an internal 1.3 V supply rail
as illustrated in Figure 30: 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 illustrated in Figure 30 and Table 22.
The ESD sensitivity rating of the
PWR_ON
pin is 1 kV (Human Body Model according to JESD22-A114).
A 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
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
the pin is equipped with an internal active pull-up resistor, as illustrated in Figure 30.
TOBY-L4 series
20
PWR_ON
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
TOBY-L4 series
35 k
1.3 V
20
PWR_ON
TP
TP
35 k
1.3 V
Figure 30: 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 22: 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, for diagnostic purposes.
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 the
TOBY-L4 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.
