User's Manual

TOBY-R2 series - System Integration Manual
UBX-16010572 - R04 Design-in
Page 83 of 147
2.3 System functions interfaces
2.3.1 Module power-on (PWR_ON)
2.3.1.1 Guidelines for PWR_ON circuit design
TOBY-R2 series PWR_ON input is equipped with an internal active pull-up resistor to the V_BCKP supply as
described in Figure 39: 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 39 and Table 29.
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
the pin is equipped with an internal active pull-up resistor to the V_BCKP supply, as described in Figure 39.
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 switch-on.
TOBY-R2 series
10 k
3
V_BCKP
20
PWR_ON
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
TOBY-R2 series
10 k
3
V_BCKP
20
PWR_ON
TP
TP
Figure 39: 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 29: 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 the
TOBY-R2 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.