Wavecom Gx64 Application Note page 23

The power supply should be an efficient converter that takes the V
whatever voltage level the source is providing and converts it to the recommended
VCC voltage level. To minimise power consumption this regulator is only enabled
when the Wireless CPU is supposed to be active.
After the application is installed the "StartUp" button is pressed to initialise the
product.
perform its own power control.
The shorting of ON/OFF to GND at the initial "StartUp" will enable the regulator
causing VCC to go high. When the Wireless CPU powers on, VREF goes high which
creates a regulator hold signal. The application is now running normally. The backup
"Button Cell" for VRTC is charged by the Wireless CPU with a minimum of 200uA as
long as VCC is active.
When the application is ready to power down it sets up the ALARM wakeup time using
"AT+CALA"-command, then shuts the Wireless CPU down using the "AT+CFUN=0"-
command. When the Wireless CPU has de-registered from the network and powered
down properly, VREF will go inactive low removing the hold signal from the VCC
regulator causing the regulator to turn off and VCC to go low. The application is now
in extreme low power mode with only VRTC being held active by the "Button Cell",
which in turn keeps the RTC active.
W hen the RTC alarm time has expired, the RTC sets the ALARM-signal low. This will
enable the VCC regulator and automatically power on the Wireless CPU.
application can now perform its scheduled activities before setting the alarm-time,
de-register, and power down.
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Gx64 APPLICATION NOTE
Power Management
Page: 23/30
This will only have to be done once.
It should be noted that the ALARM-output is referenced to VRTC. VRTC
is specified to operate down to 1.1V, but it has been tested to work
reliably down to as low as 0.8V. If the application wants the RTC to
work all the way down to that voltage it has to make sure that the
transistors used on the ALARM-output can operate reliably at such low
voltage.
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After that, the Wireless CPU will
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