OMAPL137CZKBT3 Datasheet, PDF (213/222 Pages) Texas Instruments – OMAP-L137 Low-Power Applications Processor

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OMAP-L137
SPRS563G – SEPTEMBER 2008 – REVISED JUNE 2014
6.32.1 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
load capacitance values are 10-20 pF, where the load capacitance is the series combination of C1 and
C2.
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.
RTC
Power
Source
Real Time Clock
RTC_CV_DD
C2
RTC_XI
XTAL
32.768
kHz
C1
RTC_XO
32K
OSC
Real
Time
Clock
(RTC)
Module
RTC_VSS
Isolated RTC
Power Domain
Figure 6-76. Clock Source
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Peripheral Information and Electrical Specifications 213
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