Datasheet

1.0E+02
R VALUE - LOG SCALE (:)
-14.00
-12.00
-10.00
-8.00
-6.00
-4.00
-2.00
0.00
DE-EMPH (dB)
VDD = 1.8V,
T
A
= 25
o
C
1.0E+03 1.0E+04 1.0E+05 1.0E+06
DS90UR905Q, DS90UR906Q
www.ti.com SNLS313G –SEPTEMBER 2009–REVISED APRIL 2013
EMI Reduction Features
Ser — Spread Spectrum Compatibility
The Ser PCLK is capable of tracking spread spectrum clocking (SSC) from a host source. The PCLK will accept
spread spectrum tracking up to 35kHz modulation and ±0.5, ±1 or ±2% deviations (center spread). The maximum
conditions for the PCLK input are: a modulation frequency of 35kHz and amplitude deviations of ±2% (4% total).
Signal Quality Enhancers
Ser — VOD Select (VODSEL)
The Ser differential output voltage may be increased by setting the VODSEL pin High. When VODSEL is Low,
the VOD is at the standard (default) level. When VODSEL is High, the DC VOD is increased in level. The
increased VOD is useful in extremely high noise environments and also on extra long cable length applications.
When using de-emphasis it is recommended to set VODSEL = H to avoid excessive signal attenuation especially
with the larger de-emphasis settings. This feature may be controlled by the external pin or by register.
Table 3. Differential Output Voltage
Input Effect
VODSEL VOD (mV) VOD (mVp-p)
H ±420 840
L ±280 560
Ser — De-Emphasis (De-Emph)
The De-Emph pin controls the amount of de-emphasis beginning one full bit time after a logic transition that the
Ser drives. This is useful to counteract loading effects of long or lossy cables. This pin should be left open for
standard switching currents (no de-emphasis) or if controlled by register. De-emphasis is selected by connecting
a resistor on this pin to ground, with R value between 0.5 kΩ to 1 MΩ, or by register setting. When using De-
Emphasis it is recommended to set VODSEL = H.
Table 4. De-Emphasis Resistor Value
Resistor Value (kΩ) De-Emphasis Setting
Open Disabled
0.6 - 12 dB
1.0 - 9 dB
2.0 - 6 dB
5.0 - 3 dB
Figure 21. De-Emph vs. R value
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