Micrel, Inc.

SY58607U

August 2007

6

M9999-082907-B

hbwhelp@micrel.com or (408) 955-1690

Functional Description

Fail-Safe Input (FSI)

The input includes a special failsafe 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

sufficiently

below

by the FSI function.

Input Clock Failure Case

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

low signal swing, the FSI function will eliminate a

metastable condition and guarantee a stable output.

No ringing and no undetermined state will occur at the

output under these conditions.

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

Characteristics” for detailed information.

Timing Diagrams

Figure 1a. Propagation Delay

Figure 1b. Fail Safe Feature