
Electrical Specifications
197
December 2003 Revised March 2005
SPRS231D
5.5.2 Base Oscillator (12, 13, or 19.2 MHz) and Input Clock
The internal base system oscillator is enabled following a device reset. The oscillator requires an external
crystal to be connected across the OSC1_IN and OSC1_OUT pins. If the internal oscillator is not used
(configured in software), an external clock source (12,13, 19.2 MHz) must be applied to the OSC1_IN pin, and
the OSC1_OUT pin must be left unconnected. Because the internal oscillator can be used as a clock source
to the OMAP DPLL, the 12-,13-, or 19.2-MHz crystal oscillation frequency can be multiplied to generate the
DSP clock, MPU clock, traffic controller clock.
The crystal must be in fundamental-mode operation, and parallel resonant, with a maximum effective series
resistance of 50
maximum and a power dissipation of 0.5 mW. The connection of the required circuit,
consisting of the crystal and two load capacitors, is shown in Figure 55. The load capacitors, C
1
and C
2
, must
be chosen such that the equation below is satisfied (recommended values are C
1
= C
2
= 2C
L
). C
L
in the
equation is the load specified for the crystal. All discrete components used to implement the oscillator circuit
must be placed as close as possible to the associated oscillator pins (OSC1_IN and OSC1_OUT) and to the
V
SS
pins closest to the oscillator pins (ZZG balls AA1 and Y3; ZDY balls G11 and N5).
NOTE:
The base oscillator is powered by the embedded LDO. If an external clock source is used instead of
using the on-chip oscillator, care must be taken that the voltage level driven onto the OSC1_IN pin is no greater
than the LDO voltage level.
OSC1_IN
OSC1_OUT
C1
C2
12, 13, or
19.2-MHz Crystal
C
1
= C
2
= 2C
L
(C
L
= Crystal Load Capacitance)
Figure 55. Internal System Oscillator External Crystal
If USB host function is used, it is recommended that a very low PPM crystal (
≤
50 ppm) be used for the
12,13, or 19.2 MHz oscillator circuit. If the USB host function is not used, then a crystal of
≤
180 ppm is
recommended. When selecting a crystal, the system design must take into account the temperature and aging
characteristics of a crystal versus the user environment and expected lifetime of the system.
Table 53 shows the switching characteristics of the base oscillator.
Table 53. Base Oscillator Switching Characteristics
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
UNIT
Start-up time (from power up until oscillating at stable
frequency of 12,13, or 19.2 MHz)
C1 = C2 = 10 pF, CV
DD
= 1.3V
1.7
3
ms
I
DDA
, active current consumption
C1 = C2 = 10 pF, CV
DD
= 1.5V
220
μ
A
Oscillation frequency
12 to
19.2
MHz