HCPL-261A Datasheet, PDF (17/17 Pages) Agilent(Hewlett-Packard) – HCMOS Compatible, High CMR, 10 MBd Optocouplers

The figure shows data and clock signals at the inputs and
outputs of the optocouplers. To obtain the maximum
data transmission rate, both edges of the clock signal are
being used to clock the data; if only one edge were used,
the clock signal would need to be twice as fast.
Propagation delay skew repre­sents the uncertainty of
where an edge might be after being sent through an op-
tocoupler. Figure 26 shows that there will be uncertainty
in both the data and the clock lines. It is important that
these two areas of uncer­tainty not overlap, otherwise
the clock signal might arrive before all of the data out-
puts have settled, or some of the data outputs may start
to change before the clock signal has arrived. From these
considera­tions, the absolute minimum pulse width that
can be sent through optocouplers in a parallel applica-
tion is twice t_PSK. A cautious design should use a slightly
longer pulse width to ensure that any additional uncer-
tainty in the rest of the circuit does not cause a prob-
lem.
The t_PSK specified optocouplers offer the advantages of
guaran­teed specifications for propaga­tion delays, pulse-
width distortion, and propagation delay skew over the
recommended temperature, input current, and power
supply ranges.
I_F
50%
V_O
1.5 V
TPHL
I_F
50%
V_O
1.5 V
TPLH
t _PSK
Figure 25. Illustration of propagation delay skew – t_PSK.
DATA
INPUTS
CLOCK
HCPL-261A fig 24
DATA
OUTPUTS
CLOCK
t _PSK
t _PSK
Figure 26. Parallel data transmission example.
HCPL-2602 fig 17
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Data subject to change. Copyright © 2007 Avago Technologies Limited. All rights reserved. Obsoletes AV01-0561EN
AV02-0391 - December 6, 2007