dsp56824 Freescale Semiconductor, Inc, dsp56824 Datasheet - Page 22

• Manufacturer Part Number: dsp56824
• Description: 16-bit Digital Signal Processor
• Manufacturer: Freescale Semiconductor, Inc

3.4 External Clock Operation
(V
The DSP56824 system clock can be derived from a crystal or an external system clock signal. To generate
a reference frequency using the internal oscillator, a reference crystal must be connected between the
EXTAL and XTAL pins. Figure 5 shows the transconductance model for XTAL. Table 21 shows the
electrical characteristics for EXTAL and XTAL pins.
The internal oscillator is designed to interface with a parallel-resonant crystal resonator in the frequency
range specified for the external crystal in Table 22. Figure 6 shows typical crystal oscillator circuits.
Follow the crystal supplier’s recommendations when selecting a crystal, since crystal parameters
determine the component values required to provide maximum stability and reliable start-up. The load
capacitance values used in the oscillator circuit design should include all stray layout capacitances. The
crystal and associated components should be mounted as close as possible to the EXTAL and XTAL pins
to minimize output distortion and start-up stabilization time.
When using the on-chip oscillator in conjunction with an external crystal to generate the DSP clock, the
following specifications apply. When driving the clock directly into EXTAL (not using a crystal), the input
clock should follow normal digital DSP56824 requirements.
22
EXTAL peak-to-peak swing (for any value of XCOLF)
V
V
V
XTAL transconductance
XCOLF = 0
XCOLF = V
XTAL output resistance
XCOLF = 0
XCOLF = V
DDPLL
DDPLL
DDPLL
SS
= 0 V, V
= 2.7 V
= 3.0 V
= 3.6 V
DD
DD
V
DD
in
= 2.7–3.6 V, T
g
m
Table 21. EXTAL/XTAL Electrical Characteristics
Characteristics
Figure 5. XTAL Transconductance Model
Freescale Semiconductor, Inc.
For More Information On This Product,
A
= –40 to +85 C, C
r
o
DSP56824 Technical Data
Go to: www.freescale.com
V
out
L
= 50 pF)
Symbol
g
—
—
—
r
V
m
o
in
0.206
1.27
1.38
1.58
2.06
28.3
2.83
Min
0.465
4.65
80.6
8.06
Typ
—
—
—
V
out
209.4
20.94
Max
2.75
1.02
10.2
1.9
2.1
AA0118
mA/V
mA/V
V p-p
V p-p
V p-p
Unit
k
k