AM335x
XTALIN
VSS_OSC
XTALOUT
LVCMOS
Digital
Clock
Source
VDDS_OSC
AM3359, AM3358, AM3357, AM3356, AM3354, AM3352
SPRS717H –OCTOBER 2011–REVISED MAY 2015
www.ti.com
6.2.2.2 OSC0 LVCMOS Digital Clock Source
Figure 6-11 shows the recommended oscillator connections when OSC0 is connected to an LVCMOS
square-wave digital clock source. The LVCMOS clock source is connected to the XTALIN terminal. The
ground for the LVCMOS clock source and VSS_OSC should be connected directly to the nearest PCB
digital ground (VSS). In this mode of operation, the XTALOUT terminal should not be used to source any
external components. The printed circuit board design should provide a mechanism to disconnect the
XTALOUT terminal from any external components or signal traces that may couple noise into OSC0 via
the XTALOUT terminal.
The XTALIN terminal has a 15- to 40-kΩ internal pulldown resistor which is enabled when OSC0 is
disabled. This internal resistor prevents the XTALIN terminal from floating to an invalid logic level which
may increase leakage current through the oscillator input buffer.
Figure 6-11. OSC0 LVCMOS Circuit Schematic
Table 6-4. OSC0 LVCMOS Reference Clock Requirements
NAME DESCRIPTION MIN TYP MAX UNIT
ƒ
(XTALIN)
Frequency, LVCMOS reference clock 19.2, 24, 25, MHz
or 26
Frequency, LVCMOS reference clock stability and tolerance
(1)
–50 50 ppm
t
dc(XTALIN)
Duty cycle, LVCMOS reference clock period 45% 55%
t
jpp(XTALIN)
Jitter peak-to-peak, LVCMOS reference clock period –1% 1%
t
R(XTALIN)
Time, LVCMOS reference clock rise 5 ns
t
F(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.
6.2.2.3 OSC1 Internal Oscillator Clock Source
Figure 6-12 shows the recommended crystal circuit for OSC1 of the ZCE package and Figure 6-13 shows
the recommended crystal circuit for OSC1 of the ZCZ package. It is recommended that pre-production
printed circuit board (PCB) designs include the two optional resistors R
bias
and R
d
in case they are
required for proper oscillator operation when combined with production crystal circuit components. In most
cases, R
bias
is not required and R
d
is a 0-Ω resistor. These resistors may be removed from production
PCB designs after evaluating oscillator performance with production crystal circuit components installed on
pre-production PCBs.
The RTC_XTALIN terminal has a 10- to 40-kΩ internal pullup 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.
110 Power and Clocking Copyright © 2011–2015, Texas Instruments Incorporated
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Product Folder Links: AM3359 AM3358 AM3357 AM3356 AM3354 AM3352
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