ICS581-01 Datasheet, PDF (4/10 Pages) Integrated Circuit Systems – Zero-Delay Glitch-Free Clock Multiplexer

ICS581-01/02
ZERO DELAY GLITCH-FREE CLOCK MULTIPLEXER
ZDB AND MULTIPLEXER
PLL will run in an open loop.
The ICS581-02 is identical to the ICS581-01 except for the
switching of the input mux. On the ICS581-02, the switching
is automatically controlled by a transition detector. The
transition detector monitors the clock on INA. If this clock
stops, the output of the detector, NO_INA goes high, which
then selects clock input INB to the mux. The definition of the
clock stopping is determined by a timeout selected by input
DIV. If DIV is low, NO_INA will go high after no transitions
have occurred on INA for nominally three cycles of the clock
on INB. If DIV is high, the timeout is nominally 48 cycles of
INB. When INA restarts, the mux immediately switches back
to the INA selection with no timeout.
Input Clock Frequency
The ICS581-01 and ICS581-02 are designed to switch
between two clocks of the same frequency. They will also
operate with different frequencies on each of the two input
clocks. If the two input frequencies require different input
ranges (see table on page two), then the highest range
should be permanently selected. When the selected input
clock is outside this range, jitter and input skew
specifications may not be met. Consult IDT for more
information.
Application Example
A typical application for the ICS581-02 is to provide a backup clock for a system. The backup reliable clock would
be connected to INB while the main clock would be connected to INA. If the main clock failed, the ICS581-02 would
automatically be switched to the backup clock. The following example shows the connection for this.
VDD
0.01F
MAIN
BACKUP
S0
S1
VDD
INA
INB
GND
FBIN
OE0
DIV
VDD
CLK1
CLK2
CLK3
CLK4
GND
OE1
0.01F
33
33
33
33
In this example, the clocks are 155 MHz and so the frequency range is address 11. Both S0 and S1 are left
unconnected, causing the on-chip pull-ups to produce the required high inputs. The same is true for OE0, OE1, and
DIV. In this example, CLK4 is used as the feedback. Note that the feedback path is before the series resistor.
IDT® ZERO DELAY GLITCH-FREE CLOCK MULTIPLEXER
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ICS581-01/02 REV M 110216