Requirements for a real time clock implementation are a basic clock (hours and minutes), a calender and a timer with alarm and power on/off -function and miscellaneous calls. The RTC will contain only the time base and the alarm timer but all other functions will be implemented with the MCU software. The RTC needs a power backup to keep the clock running when the phone battery is disconnected. The backup power is supplied from a rechargable polyacene battery that can keep the clock running some ten minutes. If the backup has expired, the RTC clock restarts after the main battery is connected. The CCONT keeps MCU in reset until the 32kHz source is settled (1s max).
The CCONT is an ideal place for an integrated real time clock as the asic already contains the power up/down functions and a sleep control with the 32kHz sleep clock, which is running always when the phone battery is connected. This sleep clock is used for a time source to a RTC block.
CHAPS has a current limited voltage regulator for charging a backup battery. The regulator derives its power from VOUT so that charging can take place without the need to connect a charger. The backup battery is only used to provide power to a real time clock when VOUT is not present so it is important that power to the charging circuitry is derived from VOUT and that the charging circuitry does not present a load to the backup battery when VOUT is not present.
It should not be possible for charging current to flow from the backup battery into VOUT if VOUT happens to be lower than VBACK. Charging current will gradually diminish as the backup battery voltage reaches that of the regulation voltage.
A vibra alerting device is used for giving silent signal to the user of an incoming call. The device is not placed in the phone but it will be added to a special battery pack. The vibra is controlled with a PWM signal by the MAD via the BTEMP battery terminal.
A 15kohm BSI resistor is needed to detect the vibra battery. It is only used to enable vibra selection in user menu. When alerting, VibraPWM signal is delivered to battery.
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