HCPL-0710-500E 查看數據表（PDF） - Avago Technologies

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HCPL-0710-500E

40 ns Propagation Delay, CMOS Optocoupler

Avago Technologies 

Pulse-width distortion (PWD) is the difference between

tPHL and tPLH and often determines the maxim­ um data

rate capability of a transmission system. PWD can be

expressed in percent by dividing the PWD (in ns) by

the minimum pulse width (in ns) being transm­ itted.

Typically, PWD on the order of 20 - 30% of the minimum

pulse width is tolerable. The PWD specification for the

HCPL-x710 is 8 ns (10%) maximum across recommend-

ed operating condi­tions. 10% maximum is dictated

by the most stringent of the three fieldbus standards,

PROFIBUS.

Propagation delay skew, tPSK, is an important parameter

to con­sider in parallel data applications where synchro-

nization of signals on parallel data lines is a concern. If

the parallel data is being sent through a group of op-

tocouplers, differences in propagation delays will cause

the data to arrive at the outputs of the optocouplers at

different times. If this difference in propagation delay

is large enough it will determine the maximum rate at

which parallel data can be sent through the optocou-

plers.

Propagation delay skew is defined as the differ-

ence between the minimum and maximum propa­

gation delays, either tPLH or tPHL, for any given group

of optocoup­lers that are operating under the same

conditions (i.e., the same drive current, supply volt­age,

output load, and operating temperature). As illustrated

in Figure 15,­if the inputs of a group of optocouplers

are switched either ON or OFF at the same time, tPSK is

the difference between the shortest propagation delay,

either tPLH or tPHL, and the longest propagation delay,

either tPLH or tPHL.

As mentioned earlier, tPSK can determine the maximum

parallel data transmission rate. Figure 16 is the timing

diagram of a typical parallel data application with both

the clock and data lines being sent through the opto-

couplers. The figure shows data and clock signals at the

inputs and outputs of the optocouplers. In this case, the

data is assumed to be clocked off of the rising edge of

the clock.

Propagation delay skew repre­sents the uncertain-

ty of where an edge might be after being sent

through an optocoupler. Figure 16 shows that there

will be uncertainty in both the data and clock lines.

These two areas of uncertainty must not overlap;

otherwise, the clock signal might arrive before all of

the data outputs 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 op-

tocouplers in a parallel application is twice tPSK.

A cautious design should use a slightly longer pulse

width to ensure that any additional uncertainty in the

rest of the circuit does not cause a problem.

The HCPL-x710 optocouplers offer the advantage of

guaranteed specifications for propagation delays,

pulse-width distortion, and propagation delay skew

over the recommended temperature, and power supply

ranges.

VI

50%

VO

2.5 V,

CMOS

tPSK

VI

50%

VO

2.5 V,

CMOS

Figure 15. Propagation delay skew waveform

DATA

INPUTS

CLOCK

DATA

OUTPUTS

tPSK

CLOCK

tPSK

Figure 16. Parallel data transmission example

11

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