C
2
C
1
X
1
OSCOUT
OSCIN
OSCV
SS
Clock Input
to PLL
OMAP-L137
www.ti.com
SPRS563G – SEPTEMBER 2008 – REVISED JUNE 2014
6.5
Crystal Oscillator or External Clock Input
The OMAP-L137 device includes two choices to provide an external clock input, which is fed to the on-
chip PLL to generate high-frequency system clocks. These options are illustrated in
Figure 6-6
and
Figure 6-7
. For input clock frequencies between 12 and 20 MHz, a crystal with 80 ohm max ESR is
recommended. For input clock frequencies between 20 and 30 MHz, a crystal with 60 ohm max ESR is
recommended. Typical load capacitance values are 10-20 pF, where the load capacitance is the series
combination of C1 and C2.
The CLKMODE bit in the PLLCTL register must be 0 to use the on-chip oscillator. If CLKMODE is set to 1,
the internal oscillator is disabled.
•
Figure 6-6
illustrates the option that uses on-chip 1.2V oscillator with external crystal circuit.
•
Figure 6-7
illustrates the option that uses an external 1.2V clock input.
Figure 6-6. On-Chip 1.2V Oscillator
Table 6-2. Oscillator Timing Requirements
PARAMETER
MIN
MAX
UNIT
f
osc
Oscillator frequency range (OSCIN/OSCOUT)
12
30
MHz
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