User's Manual

LISA-U1/LISA-H1 series - System Integration Manual
3G.G2-HW-10002-2 Advance Information System description
Page 32 of 116
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 kΩ) biased by the V_BCKP supply pin of the module.
Once the module has turned on, moving the PWR_ON pin has no effect. On the other hand it makes no sense
to keep this pin low once the module has been turned on: if the pin is kept low it will draw unnecessary current.
Following are some typical examples of application circuits to turn the module on using the PWR_ON input pin.
The simplest way to turn on the module is to use a push button that shorts the PWR_ON pin to ground: in this
case the V_BCKP supply pin or the VCC supply of the module can be used to bias the pull-up resistor.
If the PWR_ON input is connected to an external device (e.g. application processor), it is suggested to use an
open drain output on the external device with an external pull-up resistor (e.g. 100 kΩ) biased by the 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 voltage value as V_BCKP operating range,
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). To avoid an unwanted switch on of the module be
sure to fix the proper level on PWR_ON in all possible scenarios.
LISA-U1/LISA-H1
series
Rext
2
V_BCKP
19
PWR_ON
Power-on
push button
ESD
Open
Drain
Output
Application
Processor
LISA-U1/LISA-H1
series
Rext
2
V_BCKP
19
PWR_ON
Figure 16: PWR_ON application circuits using a push button and an open drain output of an application processor
Reference
Description
Remarks
Rext
100 kΩ Resistor 0402 5% 0.1 W
External pull-up resistor
ESD
CT0402S14AHSG - EPCOS
Varistor array for ESD protection
Table 11: Example of pull-up resistor and ESD protection for the PWR_ON application circuits
1.6.1.3 Rising edge on RESET_N
The module can be switched on by means of the RESET_N input pin: the RESET_N signal must be forced to the
low level for at least 50 ms and then released from the low level to generate a rising edge that starts the module
power-on sequence.