AM3359, AM3358, AM3357
AM3356, AM3354, AM3352
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SPRS717F –OCTOBER 2011–REVISED APRIL 2013
AM335x
XTALIN
VSS_OSC
XTALOUT
C1
C2
Crystal
Optional Rd
Optional Rbias
A. Oscillator components (Crystal, C1, C2, optional Rbias and Rd) must be located close to the AM335x package.
Parasitic capacitance to the printed circuit board (PCB) ground and other signals should be minimized to reduce noise
coupled into the oscillator. The VSS_OSC terminal provides a Kelvin ground reference for the external crystal
components. External crystal component grounds should only be connected to the VSS_OSC terminal and should not
be connected to the PCB ground plane.
B. C1 and C2 represent the total capacitance of the respective PCB trace, load capacitor, and other components
(excluding the crystal) connected to each crystal terminal. The value of capacitors C1 and C2 should be selected to
provide the total load capacitance, CL, specified by the crystal manufacturer. The total load capacitance is CL
=
[(C1*C2)/(C1+C2)] + Cshunt, where Cshunt is the crystal shunt capacitance (C0) specified by the crystal manufacturer
plus any mutual capacitance (Cpkg + CPCB) seen across the AM335x XTALIN and XTALOUT signals. For
recommended values of crystal circuit components, see Table 4-2.
Figure 4-8. OSC0 Crystal Circuit Schematic
Table 4-2. OSC0 Crystal Circuit Requirements
NAME
DESCRIPTION
MIN
TYP
MAX
UNIT
fxtal
Crystal parallel resonance
frequency
Fundamental mode oscillation only
19.2, 24.0,
25.0, or
26.0
MHz
Crystal frequency stability
and tolerance
-50.0
50.0
ppm
CC1
C1 capacitance
C2 capacitance
Shunt capacitance
12.0
12.0
24.0
24.0
5.0
pF
pF
pF
Ω
CC2
Cshunt
ESR
Crystal effective series
resistance
fxtal = 19.2 MHz, oscillator has nominal
negative resistance of 272 Ω and worst-
case negative resistance of 163 Ω
54.4
fxtal = 24.0 MHz, oscillator has nominal
negative resistance of 240 Ω and worst-
case negative resistance of 144 Ω
48.0
46.6
45.3
Ω
Ω
Ω
fxtal = 25.0 MHz, oscillator has nominal
negative resistance of 233 Ω and worst-
case negative resistance of 140 Ω
fxtal = 26.0 MHz, oscillator has nominal
negative resistance of 227 Ω and worst-
case negative resistance of 137 Ω
Copyright © 2011–2013, Texas Instruments Incorporated
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