Power off when battery voltage low

During normal discharge the phone indicates the user that the battery will drain after some time. If not recharged, the SW detects that battery voltage is too low and shuts the phone off through a normal power down procedure.

Anyway, if the SW fails to power down the phone, the CCONT resets and powers down the phone if the battery voltage drops below 2.8V.

If the MAD receives fault indication from the line TXF, that the transmitter is on although it shouldn't be, the control SW will power down the phone.

The phone can enter the SLEEP only when both the MCU and DSP request it. A substantial amount of current is saved in the SLEEP. When going to the SLEEP following things happen :

1. Both the MCU and DSP enable sleep mode, set the sleep timer and enter sleep mode

2. RFCEN and RFCSETTLED -> 0 -> COBBACLK will stop (gated in the COBBA). Also VR1 is disabled -> the VCXO supply voltage is cut off -> the RFC stops.

3. LCD display remains the same, no changes

4. Sleep clock (SLCLK) and watchdog in the CCONT running

5. Sleep counter in the MAD running, uses SLCLK

In a typical case the phone leaves the SLEEP-mode when the SLEEP-counter in MAD expires. After that MAD enables VR1 ^ the VCXO starts running ^ after a pre-programmed delay RFCSETTLED rises => the MAD receives COBBACLK clock ^ the MAD operation re-starts.

There are also many other cases when the SLEEP mode can be interrupted, in these cases the MAD enables the VR1 and operation is started similarly

- some MCU or DSP timer expires

- DSP regular event interrupt happens

- MBUS activity is detected

- FBUS activity is detected

- Charger is connected, Charger interrupt to the MAD

- any key on keyboard is pressed, interrupt to the MAD

- HEADSETINT, from system connector XMIC line (EAD)

- HOOKINT, from system connector XEAR line

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