LISA-U2 series - System integration manual
UBX-13001118 - R27
System description
Page 37 of 183
C1-Public
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 the 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 correct 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 the pin to the low level, normally high by external pull-up)
•
Rising edge on the
RESET_N
pin (i.e. releasing the pin from low level, 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 levels could be required if the line is externally accessible on the application
board. Higher protection levels can be achieved by mounting an ESD protection (e.g. EPCOS
CA05P4S14THSG varistor array) on the line connected to this pin, close to the 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
for the
VCC
normal operating range minimum limit).
☞
The voltage at the
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 suitable 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.
