Figure 25. Illustration of propagation delay skew – t

50%

1.5 V

IF

VO

50%

IF

VO

tPSK

1.5 V

HCPL-261A fig 24

TPHL

TPLH

Figure 26. Parallel data transmission example.

HCPL-2602 fig 17

DATA

INPUTS

CLOCK

DATA

OUTPUTS

CLOCK

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

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Data subject to change. Copyright © 2007 Avago Technologies Limited. All rights reserved. Obsoletes AV01-0561EN

AV02-0391 - December 6, 2007

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

longer pulse width to ensure that any additional uncer-

tainty in the rest of the circuit does not cause a prob-

lem.

The t

guaranteed specifications for propagation delays, pulse-

width distortion, and propagation delay skew over the

recommended temperature, input current, and power

supply ranges.