LISA-U1 series - System Integration Manual
3G.G2-HW-10002-3
Preliminary
System description
Page 36 of 125
1.6.2
Module power off
The correct way to switch off LISA-U1 series modules is by means of +CPWROFF AT command (more details in
u-
blox AT Commands Manual
[2]): in this way the current parameter settings are saved in the module’s non-
volatile memory and a proper network detach is performed.
An under-voltage shutdown will be done if the
VCC
supply is removed, but in this case the current parameter
settings are not saved in the module’s non-volatile memory and a proper network detach cannot be performed.
The power off sequence is described in Figure 18. When the +CPWROFF AT command is sent, the module starts
the switch-off routine replying OK on the AT interface: during this phase, the current parameter settings are
saved in the module’s non-volatile memory, a network detach is performed and all module interfaces are
disabled (i.e. the digital pins are locked in tri-state by the module). Since the time to perform a network detach
depends on the network settings, the duration of this phase can differ from the typical value reported in the
following figure. At the end of the switch-off routine, all the digital pins are locked in tri-state by the module
and all the internal LDO voltage regulators except the RTC supply (
V_BCKP
) are turned off in a defined power
off sequence. The module remains in power off mode as long as a switch on event doesn’t occur (i.e. a falling
edge on the
PWR_ON
pin or an RTC alarm), and enters not-powered mode if the supply is removed from the
VCC
pin.
VCC
V_BCKP
PWR_ON
*
V_INT
Internal Reset
System State
BB Pads State
Operational
OFF
Tristate / Floating
ON
Operational
→
Tristate / Floating
AT+CPWROFF
sent to the module
0 ms
~50 ms
~400 ms
OK
replied by the module
Figure 18: LISA Power off sequence description (* - the PWR_ON signal state is not relevant during this phase)
The Internal Reset signal is not available on a module pin.
Tristated pins are always subject to floating caused by noise: to prevent unwanted effects, fix them with
proper pull-up or pull down resistors to stable voltage rails to fix their level when the module is in Power
down state.
