Data Sheet
AM335x
(ZCZ Package)
RTC_XTALIN RTC_XTALOUT
N/C
LVCMOS
Digital
Clock
Source
VSS_RTC
VDDS_RTC
AM335x
(ZCE Package)
RTC_XTALIN RTC_XTALOUT
N/C
LVCMOS
Digital
Clock
Source
VDDS_RTC
AM3359, AM3358, AM3357
AM3356, AM3354, AM3352
SPRS717F –OCTOBER 2011–REVISED APRIL 2013
www.ti.com
4.2.2.4 OSC1 LVCMOS Digital Clock Source
Figure 4-14 shows the recommended oscillator connections when OSC1 of the ZCE package is connected
to an LVCMOS square-wave digital clock source and Figure 4-15 shows the recommended oscillator
connections when OSC1 of the ZCZ package is connected to an LVCMOS square-wave digital clock
source. The LVCMOS clock source is connected to the RTC_XTALIN terminal. In this mode of operation,
the RTC_XTALOUT terminal should not be used to source any external components. The printed circuit
board design should provide a mechanism to disconnect the RTC_XTALOUT terminal from any external
components or signal traces that may couple noise into OSC1 via the RTC_XTALOUT terminal.
The RTC_XTALIN terminal has a 10 - 40 kΩ internal pull-up resistor which is enabled when OSC1 is
disabled. This internal resistor prevents the RTC_XTALIN terminal from floating to an invalid logic level
which may increase leakage current through the oscillator input buffer.
Figure 4-14. OSC1 (ZCE Package) LVCMOS Circuit Schematic
Figure 4-15. OSC1 (ZCZ Package) LVCMOS Circuit Schematic
Table 4-7. OSC1 LVCMOS Reference Clock Requirements
NAME DESCRIPTION MIN TYP MAX UNIT
f
(RTC_XTALIN)
Frequency, LVCMOS reference clock 32.768 MHz
Frequency, LVCMOS reference clock Maximum RTC error = -20 20 ppm
stability and tolerance
(1)
10.512 minutes/year
Maximum RTC error = 26.28 -50 50 ppm
minutes/year
t
dc(RTC_XTALIN)
Duty cycle, LVCMOS reference clock period 45 55 %
t
jpp(RTC_XTALIN)
Jitter peak-to-peak, LVCMOS reference clock period -1 1 %
t
R(RTC_XTALIN)
Time, LVCMOS reference clock rise 5 ns
t
F(RTC_XTALIN)
Time, LVCMOS reference clock fall 5 ns
(1) Initial accuracy, temperature drift, and aging effects should be combined when evaluating a reference clock for this requirement.
112 Power and Clocking Copyright © 2011–2013, Texas Instruments Incorporated
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