Micrel, Inc.

SY58610U

November 2006

6

M9999-111406-A

Functional Description

Fail-Safe Input (FSI)

The input includes a special fail-safe circuit to sense

the amplitude of the input signal and to latch the

outputs when there is no input signal present, or

when the amplitude of the input signal drops

limited by the FSI function.

Input Clock Failure Case

If the input clock fails to a floating, static, or extremely

low signal swing, such that the voltage swing across

the input pair is less than 100mV, the FSI function will

eliminate a metastable condition and latch the outputs

to the last valid state. No ringing and no undetermined

state will occur at the output under these conditions.

The output recovers to normal operation once the

input signal returns to a valid state with a swing

greater than 100mV.

Note that the FSI function will not prevent duty cycle

distortion in case of a slowly deteriorating (but still

toggling) input signal. Due to the FSI function, the

propagation delay will depend on rise and fall time of

the input signal and on its amplitude. Refer to “Typical

Operating Characteristics” for detailed information.

Timing Diagrams

Figure 1a. Fail Safe Feature

Figure 1b. Propagation Delay IN-to-Q