AM1808_1112 Datasheet, PDF (73/262 Pages) Texas Instruments – AM1808 ARM Microprocessor

AM1808
www.ti.com
SPRS653C – FEBRUARY 2010 – REVISED DECEMBER 2011
5.5 Crystal Oscillator or External Clock Input
The device includes two choices to provide an external clock input, which is fed to the on-chip PLLs to
generate high-frequency system clocks. These options are illustrated in Figure 5-6 and Figure 5-7. 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 5-6 illustrates the option that uses on-chip 1.2V oscillator with external crystal circuit. Figure 5-7
illustrates the option that uses an external 1.2V clock input.
C₂
OSCIN
X₁
OSCOUT
C₁
Clock Input
to PLL
OSCV_SS
Figure 5-6. On-Chip Oscillator
Table 5-2. Oscillator Timing Requirements
PARAMETER
f_osc
Oscillator frequency range (OSCIN/OSCOUT)
MIN
MAX
UNIT
12
30
MHz
Copyright © 2010–2011, Texas Instruments Incorporated
Peripheral Information and Electrical Specifications
73
Submit Documentation Feedback
Product Folder Link(s): AM1808