Installation Instructions

LISA-U2 series - System Integration Manual
UBX-13001118 - R19 Early Production Information System description
Page 36 of 175
1.6 System functions
1.6.1 Module power-on
When the LISA-U2 series modules are in the not-powered mode (i.e. switched off with the VCC module supply
not applied), they can be switched on by:
 Rising edge on the VCC pin to a valid voltage as module supply (i.e. applying module supply)
 Alternately, the RESET_N pin can be held to the low level during the VCC rising edge, so that the module
switches on releasing the RESET_N pin when the VCC module supply voltage stabilizes at its proper nominal
value within the normal operating range
The status of the PWR_ON input pin of LISA-U2 series modules while applying the VCC module supply is not
relevant: during this phase the PWR_ON pin can be set high or low by the external circuit.
When the LISA-U2 series modules are in the power-off mode (i.e. switched off by means of the AT+CPWROFF
command, with valid VCC module supply applied), they can be switched on by:
 Low pulse on the PWR_ON pin (i.e. forcing to the low level the pin normally high by external pull-up)
 Rising edge on the RESET_N pin (i.e. releasing from low level the pin, normally high by internal pull-up)
 RTC alarm (i.e. pre-programmed scheduled time by AT+CALA command)
Name
Description
Remarks
PWR_ON
Power-on input
PWR_ON pin has high input impedance.
Do not keep floating in noisy environment: external pull-up
required.
Table 16: Power-on pin
The PWR_ON pin ESD sensitivity rating is 1 kV (Human Body Model according to JESD22-A114F). Higher
protection level could be required if the line is externally accessible on the application board. Higher
protection level can be achieved by mounting an ESD protection (e.g. EPCOS CA05P4S14THSG varistor
array) on the line connected to this pin, close to accessible point.
1.6.1.1 Rising edge on VCC
Applying a proper supply to VCC pins, the module supply supervision circuit controls the subsequent activation
of the power up state machines: the module is switched on when the voltage rises up to the VCC normal
operating range minimum limit starting from a voltage value lower than 2.25 V (see LISA-U2 series Data
Sheet [1] for the VCC normal operating range minimum limit).
The voltage at VCC pins must ramp from 2.5 V to 3.2 V within 1 ms to properly switch on the module.
If the external supply circuit is not able to provide this VCC voltage slope, keep the RESET_N input low
during the VCC rising edge, so that the module switches on, releasing the RESET_N pin when the VCC
voltage stabilizes at its nominal value within the normal operating range.
The status of the PWR_ON input pin during the VCC apply phase is not relevant: LISA-U2 modules switch on
when a proper rising edge on the VCC pin is applied, during this phase the PWR_ON pin can be set high or low
by the external circuit.