User's Manual

Confidential
INTERFACE DESCRIPT
29(31)
Document number Revision
1/155 19-KRD 104 1025 Uen PA4
6.2 Power Off Sequence
This sequence illustrates the power off procedure.
Figure 6.2-1 Power Off Sequence
Sequence Detail:
1 The “AT+CFUN=4” instruction is sent from the host application to the modem in
order to initiate a deregistration sequence.
2 The modem responds to the request with an ‘OK’ to indicate that deregistration
is completed. Deregistration from the network can take from 3-30 seconds.
After de-registration has been acknowledged the host application may remove
P_EN.
3 The switching regulator output capacitor will gradually discharge until the modem
regulators threshold is exceeded. and power down will be complete. VREF may
be used as indicator of complete shut down.
4 When the modem has successful shutdown, and VREF has fallen bellow 0.5V
then the host may safely remove VIN and 3V3 at any time. However the
supplies can remain active without increasing current consumption (typically
<25uA).