Datasheet
C1 C2
sys_xtalin
sys_xtalout VSSOSC
Crystal
26 MHz
AM3517, AM3505
www.ti.com
SPRS550E –OCTOBER 2009–REVISED MARCH 2013
A. Oscillator components (Crystal, C
1
, C
2
) must be located close to the AM35x package. Parasitic capacitance to the
printed circuit board (PCB) ground and other signals should be minimized to reduce noise coupled into the oscillator.
The VSSOSC terminal provides a Kelvin ground reference for the external crystal components. External crystal
component grounds should only be connected to the VSSOSC terminal and should not be connected to the PCB
ground plane.
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 AM3517/05 sys_xtalin and sys_xtalout signals. For
recommended values of crystal circuit components, see Table 4-1.
Figure 4-3. AM3517/05 Oscillator Connections
Table 4-1. Crystal Electrical Characteristics
PARAMETER MIN TYP MAX UNIT
Oscillation frequency 26 MHz
Crystal ESR 50 Ω
Frequency stability +/- 50 ppm
Parallel Load Capacitance 20 pF
(C1 and C2)
Shunt Capacitance 5 pF
4.2 Input Clock Specifications
The clock system accepts three input clock sources:
• 32-kHz digital CMOS clock
• Crystal oscillator clock or CMOS digital clock (26 MHz)
• Alternate clock (48 or 54 MHz, or other up to 54 MHz)
Table 4-2. 26-MHz SYS_CLK Input Clock Timing Requirements
PARAMETER DESCRIPTION MIN TYP MAX UNIT
f(xtalin) Frequency, sys_xtalin 26 MHz
tw(xtalin) Duty Cycle, 45 55 %
sys_xtalin
tj(xtalin) Jitter, sys_xtalin -1 1 %
tt(xtalin) Transition time, 5 ns
sys_xtalin
Copyright © 2009–2013, Texas Instruments Incorporated Clock Specifications 93
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