Installation Instructions

LISA-U2 series - System Integration Manual

UBX-13001118 - R19 Early Production Information System description

Page 37 of 175

1.6.1.2 Low pulse on PWR_ON

When the module is in power-off mode, i.e. it has been properly switched off as described in the section 1.6.2

(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 LISA-U2 series Data

Sheet [1].

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 LISA-U2 series Data Sheet [1].

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.

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 kΩ) 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 Supply/Power pins table in LISA-U2 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

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.

Open

Drain

Output

Application

processor

LISA-U2 series

Rext

V_BCKP

PWR_ON

Figure 17: PWR_ON application circuits using an open drain output of an application processor

Reference

Description

Remarks

Rext

100 kΩ Resistor 0402 5% 0.1 W

External pull-up resistor

Table 17: Example of pull-up resistor for the PWR_ON application circuit