AM335x
XTALIN
VSS_OSC
XTALOUT
C
1
C
2
Optional R
d
Crystal
Optional R
bias
AM3359, AM3358, AM3357, AM3356, AM3354, AM3352
SPRS717H – OCTOBER 2011 – REVISED MAY 2015
A.
Oscillator components (Crystal, C
1
, C
2
, optional R
bias
and R
d
) must be located close to the AM335x package.
Parasitic capacitance to the VSS_OSC and respective crystal circuit component grounds should be connected directly
to the nearest PCB digital ground (VSS).
B.
C
1
and C
2
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 C
1
and C
2
should be selected to
provide the total load capacitance, C
L
, specified by the crystal manufacturer. The total load capacitance is C
L
= [(C
1
×
C
2
) / (C
1
+ C
2
)] + C
shunt
, where C
shunt
is the crystal shunt capacitance (C
0
) specified by the crystal manufacturer plus
any mutual capacitance (C
pkg
+ C
PCB
) seen across the AM335x XTALIN and XTALOUT signals. For recommended
values of crystal circuit components, see
.
Figure 6-9. OSC0 Crystal Circuit Schematic
Table 6-2. OSC0 Crystal Circuit Requirements
PARAMETER
MIN
TYP
MAX
UNIT
ƒ
xtal
Crystal parallel resonance
Fundamental mode oscillation only
19.2, 24,
MHz
frequency
25, or 26
Crystal frequency stability
–50
50
ppm
and tolerance
(1)
C
shunt
≤
5 pF
12
24
C
C1
C
1
capacitance
pF
C
shunt
> 5 pF
18
24
C
shunt
≤
5 pF
12
24
C
C2
C
2
capacitance
pF
C
shunt
> 5 pF
18
24
C
shunt
Shunt capacitance
7
pF
ESR
Crystal effective series
ƒ
xtal
= 19.2 MHz, oscillator has nominal
54.4
Ω
resistance
negative resistance of 272
Ω
and worst-
case negative resistance of 163
Ω
ƒ
xtal
= 24 MHz, oscillator has nominal
48.0
Ω
negative resistance of 240
Ω
and worst-
case negative resistance of 144
Ω
ƒ
xtal
= 25 MHz, oscillator has nominal
46.6
Ω
negative resistance of 233
Ω
and worst-
case negative resistance of 140
Ω
ƒ
xtal
= 26 MHz, oscillator has nominal
45.3
Ω
negative resistance of 227
Ω
and worst-
case negative resistance of 137
Ω
(1)
Initial accuracy, temperature drift, and aging effects should be combined when evaluating a reference clock for this requirement.
108
Power and Clocking
Copyright © 2011–2015, Texas Instruments Incorporated
Product Folder Links: