Ublox LISA-U100, Integration Manual, Page: 40 / 190

LISA-U series - System Integration Manual
UBX-13001118 - R17 Advance information System description
Page 40 of 190
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-U1 series Data
Sheet [1] and LISA-U2 series Data Sheet [2].
The electrical characteristics of the PWR_ON input pin are slightly different between LISA-U1 series and LISA-U2
series modules, and are different from the other digital I/O interfaces: the low level pulse time period is different,
the input voltage thresholds are slightly different and both LISA-U1 series and LISA-U2 series
PWR_ON
input pin
are tolerant of voltages up to the module supply level. The detailed electrical characteristics are described in
LISA-U1 series Data Sheet [1] and LISA-U2 series Data Sheet [2].
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 Supply/Power pins table in LISA-U1 series Data Sheet [1]
and LISA-U2 series Data Sheet [2]), 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-U series
Rext
2
V_BCKP
19
PWR_ON
Figure 18: 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 18: Example of pull-up resistor for the PWR_ON application circuit