ICS527-04 Datasheet, PDF (3/9 Pages) Integrated Circuit Systems – Clock Slicer User Configurable PECL input Zero Delay Buffer

ICS527-04
Clock Slicer User Configurable PECL input Zero Delay Buffer
External Components
Decoupling Capacitors
The ICS527-04 requires two 0.01µF decoupling
capacitors to be connected between VDD and GND,
one on each side of the chip. They must be connected
close to the device to minimize lead inductance. The
output levels can be adjusted for different output and
load impedances. Refer to application note MAN09 for
more information on the RES and resistor network
values for the output clocks.
PECL Termination Networks
The PECLO to FBPECL and PECLO to FBPECL
connections should be made directly underneath the
device, unless feedback is being routed through other
devices. The resistor divider networks should be placed
as close to the outputs as possible.
Typical 50 Ω termination is shown in the Block Diagram
on page 1. For other termination schemes, see
MAN09.pdf.
Eliminating the Delay Through Buffers or
Other Components
More complicated feedback schemes can be used,
such as incorporating low skew, multiple output buffers
in the feedback path. An example of this is given later in
the datasheet. The fundamental property of the
ICS527-04 is that it aligns rising edges on CLKIN and
FBPECL at a ratio determined by the reference and
feedback dividers. This means that any delay in the
feedback path will cause the PECL output edge to lead
PECLIN by the delay amount. So, by taking the PECL
output from another device as the input to FBPECL, the
delay through the other device can be eliminated.
Setting the Clock Slicer
Use IRANGE to select the input frequency range. If
either the PECLIN or FBPECL pair frequencies are
greater than (or equal to) 80 MHz, connect IRANGE to
VDD, or let it float. If both frequencies are less than 80
MHz, connect IRANGE to ground.
Choose S1 and S0 from the table on page 2,
depending on the output frequency.
Finally, the divider settings should be selected.
Following is a description of how the dividers should be
set.
Determining ICS527-04 Divider Settings
The user has full control in setting the desired output
clock over the range shown in the table on page 2. The
user should connect the divider select input pins
directly to ground (or VDD, although this is not required
because of internal pull-ups) during Printed Circuit
Board layout, so that the ICS527-04 automatically
produces the correct clock when all components are
soldered. It is also possible to connect the inputs to
parallel I/O ports in order to switch frequencies. The
configuration inputs: IRANGE, S1, S0, R6...0, F6...0
are compatible with CMOS or TTL levels.
The output of the ICS527-04 can be determined by the
following simple equation:
FB
Frequency
=
Input
Frequency
×
-F----D----W-------+-----2--
RDW + 2
Where:
Reference Divider Word (RDW) = 0 to 127
Feedback Divider Word (FDW) = 0 to 127
FB Frequency is the same as the output
frequency
Additionally, the following operating ranges should be
observed:
300kHz < ^{I--n---p----u---t----F---r--e----q---u---e----n---c---y-}
RDW + 2
S1 and S0 should be selected depending on the
output frequency. The table on page 2 gives the
ranges.
The dividers are expressed as integers. For example, if
a 50 MHz output on CLK1 is desired from a 40 MHz
input, the reference divider word (RDW) should be 2
and the feedback divider word (FDW) should be 3
which gives the required 5/4 multiplication. If multiple
choices of dividers are available, then the lowest
numbers should be used. In this example, the output
divide (OD) should be selected to be 2. Then R6:R0 is
0000010, F6:F0 is 0000011 and S1:S0 is 00.
If you need assistance determining the optimum divider
settings, please send an e-mail to [e-mail]
with the desired input clock and the desired output
frequency.
MDS 527-04 D
3
Revision 122804
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