sy56020r Micrel Semiconductor, sy56020r Datasheet - Page 7

• Manufacturer Part Number: sy56020r
• Description: Low Voltage 1.2v/1.8v/2.5v Cml 1 4 Fanout Buffer 6.4gbps With Equalization
• Manufacturer: Micrel Semiconductor

Interface Applications
For Input Interface Applications see Figures 4a-e and
for CML Output Termination, see Figures 5a-d.
CML Output Termination with VCCO 1.2V
For VCCO of 1.2V, Figure 5a, terminate the output
with 50Ω to 1.2V, DC coupled, not 100Ω differentially
across the outputs.
If AC-coupling is used, Figure 5d, terminate into 50Ω
to 1.2V before the coupling capacitor and then
connect to a high value resistor to a reference
voltage.
Do not AC-couple with internally terminated receiver.
For example, 50Ω ANY-IN input. AC-coupling will
offset the output voltage by 200mV and this offset
voltage will be too low for proper driver operation. Any
unused output pair needs to be terminated when
VCCO is 1.2V, do not leave floating.
Timing Diagrams
October 2008
Figure 1. Propagation Delay
CML Output Termination with VCCO 1.8V, 2.5V
For VCCO of 1.8V, Figure 5a and Figure 5b,
terminate either with 50 ohms to VCCO or 100 ohms
differentially across the outputs. AC- or DC-coupling
is fine. For best signal integrity, terminate any unused
output pairs.
Input Termination
From 1.8V CML driver: Terminate input with VT tied to
1.8V. Don’t terminate 100 ohms differentially.
From 2.5V CML driver: Terminate input with either VT
tied to 2.5V or 100 ohms differentially.
The input cannot be DC-coupled from a 1.2V CML
driver.
Input AC-Coupling
The SY56020R input can accept AC-coupling from
any driver. Bypass VT with a 0.1µF low ESR capacitor
to VCC as shown in Figures 4c and 4d. VT has an
internal high impedance resistor divider as shown in
Figure 2a, to provide a bias voltage for AC-coupling.
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