u-blox SARA-G3 Series, Руководство по системной интеграции

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SARA-G3 series - System Integration Manual
UBX-13000995 - R06 Objective Specification Design-in
Page 106 of 218
2.2 System functions interfaces
2.2.1 Module power-on (PWR_ON)
2.2.1.1 Guidelines for PWR_ON circuit design
Connecting the PWR_ON input to a push button that shorts the PWR_ON pin to ground, provide an
external pull-up resistor (e.g. 100 k
Ω
) biased by the V_BCKP supply pin of the module, as described
in Figure 33Figure 33 and Table 19Table 19 . 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, provide an additional ESD protection (e.g. EPCOS CA05P4S14THSG varistor array) on the
line connected to this pin, close to accessible point.
The PWR_ON pin has high input impedance and is weakly pulled to the high level on the module.
Avoid keeping it floating in a noisy environment. To hold the high logic level stable, the PWR_ON
pin must be connected to a pull-up resistor (e.g. 100 k
Ω
) biased by the V_BCKP supply pin of
the module.
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. Higher protection
level can be achieved by mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor
array) close to accessible point.
When connecting the
PWR_ON input to an external device (e.g. application processor), use an open
drain output on the external device with an external pull-up resistor (e.g. 100 k
Ω
) biased by the
V_BCKP supply pin of the module, as described in Figure 33Figure 33 and Table 19Table 19 .
A compatible push-pull output of an application processor can also be used: in this case the pull-up can
be provided to pull the
PWR_ON level high when the application processor is switched off. If the high-
level voltage of the push-pull output pin of the application processor is greater than the maximum input
voltage operating range of the
V_BCKP pin (refer to SARA-G3 series Data Sheet [1]), the V_BCKP
supply cannot be used to bias the pull-up resistor: the supply rail of the application processor or the
module
VCC supply could be used, but this increases the V_BCKP (RTC supply) current consumption
when the module is in not-powered mode ( VCC supply not present). Using a push-pull output of the
external device, take care to fix the proper level in all the possible scenarios to avoid an inappropriate
module switch-on.