LISA-U2 series - System integration manual
UBX-13001118 - R27
System description
Page 38 of 183
C1-Public
1.6.1.2
Low pulse on PWR_ON
When the module is in power-off mode, i.e. it has been cleanly switched off as described in the section
(e.g. by the AT+CPWROFF command) and a voltage within the operating range is maintained at
the
VCC
pins, the module can be switched on by means of the
PWR_ON
input pin: a falling edge must
be provided on the
PWR_ON
pin, which must be then held low for an appropriate time period as
specified in the LISA-U2 series data sheet
The electrical characteristics of the
PWR_ON
input pin are different from the other digital I/O
interfaces; the detailed electrical characteristics are described in the LISA-U2 series data sheet
☞
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.
Following are some typical examples of application circuits to turn the module on using the
PWR_ON
input pin.
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
V_BCKP
supply
pin of the module.
A push-pull output of an application processor can also be used: in this case the pull-up can be used
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 (see the
V_BCKP
input characteristics of the supply/power pins
table in the LISA-U2 series data sheet
), the
V_BCKP
supply cannot be used to bias the pull-up
resistor: the supply rail of the application processor or the
VCC
supply could be used, but this will
increase 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 switch-on of the module.
1:1 scaling
Open
Drain
Output
Application
processor
LISA-U2 series
Rext
2
V_BCKP
19
PWR_ON
Figure 17: PWR_ON application circuits using an open drain output of an application processor
Reference
Description
Remarks
Rext
100 k
Ω
Resistor 0402 5% 0.1 W
External pull-up resistor
Table 17: Example of pull-up resistor for the PWR_ON application circuit