Rtc(32.768Khz Crystal) - LG KG271 Service Manual

3.4 RTC(32.768KHz Crystal)

The integrated Real Time Clock (RTC) is able to provide programmable alarm functions and external
interrupts. Due to its extreme low power consumption the RTC can be supplied from a small backup
battery. This allows the generation of external interrupts, even when the main PMB7880 supply
voltage is switched off. For this purpose the RTC is powered by own voltage supply pins VDD_RTC
and VSS_RTC.
The RTC shall be driven by a 32.768 kHz (32k) clock which needs to be applied via the PMB7880
F32K and OSC32K pins. The clock can be fed from either an external clock source or use the on chip
32 KHz oscillator module.
The low clock frequency and the optimized low power design give the possibility to run the chip with a
minimum of power dissipation. For example, for this specific application the 26 MHz reference
oscillator can be switched off during system standby and a lowpower time reference can be kept when
the 32k clock is provided to the RTC.
The RTC consists of an PMB7880 specific RTC shell, containing the RTC macro, as well as the 32
kHz oscillator, as described in the following sections. The module RTC Shell solely performs level
translation of the 32KHz clock to the VDD_LD1 power supply domain, and is not functionally
associated with the RTC.
32.768KHZ CRYSTAL
32KIN
32KOUT
Figure. 3-4 E-Gold Voice RTC Interface
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3. TECHNICAL BRIEF
X100
3
4
1 2
MC-146_12_5PF
32.768KHz