Micrel, Inc.

SY58608U

October 2006

6

M9999-102706-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

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 differential voltage

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

indeterminate 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 differential voltage ≥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

Characteristics” for detailed information.

Timing Diagrams

Figure 1a. Propagation Delay

Figure 1b. Fail Safe Feature