Micrel, Inc.

SY56011R

July 2008

7

M9999-070208-A

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 50 Ohms to 1.2V, not 100 ohms differentially

across the outputs. If AC-coupling is used, Figure 5d,

terminate into 50 ohms to 1.2V before the coupling

capacitor and then connect to a high value resistor to

a reference voltage. Any unused output pair needs to

be terminated, do not leave floating.

CML Output Termination with VCCO 1.8V

For VCCO of 1.8V, Figure 5a and Figure 5b,

terminate either with 50 ohms to 1.8V or 100 ohms

differentially across the outputs. AC- or DC-coupling

is fine. For best signal integrity, terminate any unused

output pairs.

Input Termination

1.8V CML driver: Terminate input with VT tied to 1.8V.

Don’t terminate 100 ohms differentially.

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.

Timing Diagrams

Figure 1. Propagation Delay