DS90UB903QSQ Datasheet, PDF (35/45 Pages) Texas Instruments – DS90UB903Q/DS90UB904Q 10 - 43MHz 18 Bit Color FPD-Link III Serializer and Deserializer

DS90UB903Q, DS90UB904Q
www.ti.com
SNLS332E – JUNE 2010 – REVISED APRIL 2013
rate increases as the cable length decreases. Therefore, the chipset supports 50 MHz at shorter distances. Other
cable parameters that may limit the cable's performance boundaries are: cable attenuation, near-end crosstalk
and pair-to-pair skew. The maximum length of cable that can be used is dependant on the quality of the cable
(gauge, impedance), connector, board (discontinuities, power plane), the electrical environment (e.g. power
stability, ground noise, input clock jitter, PCLK frequency, etc.) and the application environment.
The resulting signal quality at the receiving end of the transmission media may be assessed by monitoring the
differential eye opening of the CMLOUT P/N output. A differential probe should be used to measure across the
termination resistor at the CMLOUT P/N pins.
For obtaining optimal performance, we recommend:
• Use Shielded Twisted Pair (STP) cable
• 100Ω differential impedance and 24 AWG (or lower AWG) cable
• Low skew, impedance matched
• Ground and/or terminate unused conductors
Figure 39 shows the Typical Performance Characteristics demonstrating various lengths and data rates using
Rosenberger HSD and Leoni DACAR 538 Cable.
70
1960
60
1680
50
1400
40
30
DS90UB903Q/904Q
20
1120
840
560
10
280
0
0
0
5
10
15
20
25
CABLE LENGTH (m)
*Note: Equalization is enabled for cable lengths greater than 7 meters
Figure 39. Rosenberger HSD & Leoni DACAR 538 Cable Performance
PCB LAYOUT AND POWER SYSTEM CONSIDERATIONS
Circuit board layout and stack-up for the Ser/Des devices should be designed to provide low-noise power feed to
the device. Good layout practice will also separate high frequency or high-level inputs and outputs to minimize
unwanted stray noise pickup, feedback and interference. Power system performance may be greatly improved by
using thin dielectrics (2 to 4 mils) for power / ground sandwiches. This arrangement provides plane capacitance
for the PCB power system with low-inductance parasitics, which has proven especially effective at high
frequencies, and makes the value and placement of external bypass capacitors less critical. External bypass
capacitors should include both RF ceramic and tantalum electrolytic types. RF capacitors may use values in the
range of 0.01 uF to 0.1 uF. Tantalum capacitors may be in the 2.2 uF to 10 uF range. Voltage rating of the
tantalum capacitors should be at least 5X the power supply voltage being used.
Surface mount capacitors are recommended due to their smaller parasitics. When using multiple capacitors per
supply pin, locate the smaller value closer to the pin. A large bulk capacitor is recommend at the point of power
entry. This is typically in the 50uF to 100uF range and will smooth low frequency switching noise. It is
recommended to connect power and ground pins directly to the power and ground planes with bypass capacitors
connected to the plane with via on both ends of the capacitor. Connecting power or ground pins to an external
bypass capacitor will increase the inductance of the path.
A small body size X7R chip capacitor, such as 0603, is recommended for external bypass. Its small body size
reduces the parasitic inductance of the capacitor. The user must pay attention to the resonance frequency of
these external bypass capacitors, usually in the range of 20-30 MHz. To provide effective bypassing, multiple
capacitors are often used to achieve low impedance between the supply rails over the frequency of interest. At
high frequency, it is also a common practice to use two vias from power and ground pins to the planes, reducing
the impedance at high frequency.
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