AM1707 datasheet(191/198 Pages) TI

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XTAL

32.768

kHz

RTC_X1

RTC_X0

RTC_VSS

32K

OSC

Real

Time

Clock

(RTC)

Module

IsolatedRTC

PowerDomain

SwitchforDevice

CorePower

RealTimeClock

+1.2V

CVDD

RTC_CVDD

AM1707

www.ti.com

SPRS637A – FEBRUARY 2010 – REVISED APRIL 2010

6.33.1 Clock Source

The clock reference for the RTC is an external 32.768-kHz crystal or an external clock source of the same

frequency. The RTC also has a separate power supply that is isolated from the rest of the system. When

the CPU and other peripherals are without power, the RTC can remain powered to preserve the current

time and calendar information.

The source for the RTC reference clock may be provided by a crystal or by an external clock source. The

RTC has an internal oscillator buffer to support direct operation with a crystal. The crystal is connected

between pins RTC_XI and RTC_XO. RTC_XI is the input to the on-chip oscillator and RTC_XO is the

output from the oscillator back to the crystal. A crystal with 70k-ohm max ESR is recommended. Typical

C1, C2 values are 10-20 pF.

An external 32.768-kHz clock source may be used instead of a crystal. In such a case, the clock source is

connected to RTC_XI, and RTC_XO is left unconnected.

If the RTC is not used, the RTC_XI pin should be static held high or low and RTC_XO should be left

unconnected.

Figure 6-76. Clock Source

Peripheral Information and Electrical Specifications

191

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