sy89468u Micrel Semiconductor, sy89468u Datasheet - Page 7

• Manufacturer Part Number: sy89468u
• Description: Sy89468u Precision Lvds 1 20 Fanout With 2 1 Mux And Internal Termination With Fail Safe Input
• Manufacturer: Micrel Semiconductor

Functional Description
Clock Select (SEL)
SEL is an asynchronous TTL/CMOS compatible input
that selects one of the two input signals. An internal
25kΩ pull-up resistor defaults the input to logic HIGH if
left open. Input switching threshold is V
Figure 1a.
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 sufficiently
below 100mV
Input Clock Failure Case
If the input clock fails to a floating, static, or extremely
low signal swing such that the voltage across the input
pair is significantly less than 100mV, FSI
January 2008
PK
, typically 30mV
PK
. Refer to Figure 1b.
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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 typical swing greater than 30mV.
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 the rise and fall time
of the input signal and on its amplitude.
Output Enable (OE)
OE is a synchronous TTL/CMOS-compatible input
that enables/disables the outputs based upon the
input to this pin. The enable function is synchronous
so that the clock outputs will be enabled or disabled
following a rising and a falling edge of the input clock.
Refer to Figure 1c. Internal 25kΩ pull-up resistor
defaults the input to logic HIGH if left open. Input
switching threshold is V
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