IDT / ICS LVHSTL FREQUENCY SYNTHESIZER
14
ICS8427DY-02 REV A OCTOBER 13, 2006
ICS8427-02
500MHZ, LOW JITTER, LVCMOS/CRYSSTAL-TO-LVHSTL FREQUENCY SYNTHESIZER
EXPOSED PAD
Expose Metal Pad
(GROUND PAD)
GROUND PLANE
SOLDER
SIGNAL
TRACE
SIGNAL
TRACE
THERM AL VIA
SOLDER M ASK
FIGURE 6. P.C. BOARD FOR EXPOSED PAD THERMAL RELEASE PATH EXAMPLE
THERMAL RELEASE PATH
The expose metal pad provides heat transfer from the device to
the P.C. board. The expose metal pad is ground pad connected
to ground plane through thermal via. The exposed pad on the
device to the exposed metal pad on the PCB is contacted through
solder as shown in
Figure 6. For further information, please refer
to the Application Note on Surface Mount Assembly of Amkor’s
Thermally /Electrically Enhance Leadframe Base Package, Amkor
Technology.
Spread-spectrum clocking is a frequency modulation technique
for EMI reduction. When spread-spectr um is enabled, a
32.55kHz triangle waveform is used with 0.5% down-spread
(+0.0% / -0.5%) from the nominal 200MHz clock frequency. An
example of a triangle frequency modulation profile is shown in
Figure 5A below. The ramp profile can be expressed as:
Fnom = Nominal Clock Frequency in Spread OFF mode
(200MHz with 16.6667MHz IN)
Fm = Nominal Modulation Frequency
= Reference Frequency
16 x 32
δ = Modulation Factor (0.5% down spread)
The ICS8427-02 triangle modulation frequency deviation will
not exceed 0.6% down-spread from the nominal clock fre-
quency (+0.0% / -0.5%). An example of the amount of down
spread relative to the nominal clock frequency can be seen in
the frequency domain, as shown in
Figure 7B. The ratio of this
width to the fundamental frequency is typically 0.4%, and will
not exceed 0.6%. The resulting spectral reduction will be greater
than 7dB, as shown in Figure 7B. It is important to note the
ICS8427-02 7dB minimum spectral reduction is the compo-
nent-specific EMI reduction, and will not necessarily be the
same as the system EMI reduction.
FIGURE 7B. 200MHZ CLOCK OUTPUT IN FREQUENCY DOMAIN
(A) SPREAD-SPECTRUM OFF
(B) SPREAD-SPECTRUM ON
FIGURE 7A. TRIANGLE FREQUENCY MODULATION
SPREAD SPECTRUM
Fnom
(1 -
δ) Fnom
0.5/fm
1/fm
BA
10 dBm
δ = 0.3%
(1 -
δ) fnom + 2 fm x δ x fnom x t when 0 < t <
,
(1 -
δ) fnom - 2 fm x δ x fnom x t when
< t <
1
2 fm
1
2 fm
1
fm