ACPL-074L-500E Avago Technologies US Inc., ACPL-074L-500E Datasheet - Page 10

• Manufacturer Part Number: ACPL-074L-500E
• Description: Amplifier-Output Optocoupler,2-CHANNEL,3.75kV ISOLATION,SO
• Manufacturer: Avago Technologies US Inc.

Specifications of ACPL-074L-500E

• Voltage - Isolation: 3750Vrms
• Number Of Channels: 2, Unidirectional
• Current - Output / Channel: 10mA
• Data Rate: 15MBd
• Propagation Delay High - Low @ If: 29ns @ 14mA
• Current - Dc Forward (if): 20mA
• Input Type: DC
• Output Type: Push-Pull, Totem-Pole
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

V
V
Propagation Delay, Pulse-Width Distortion and Propa-
gation Delay Skew
Propagation delay is a figure of merit which describes how
quickly a logic signal propagates through a system. The
propagation delay from low to high (t
of time required for an input signal to propagate to the
output, causing the output to change from low to high.
Similarly, the propagation delay from high to low (t
the amount of time required for the input signal to propa-
gate to the output, causing the output to change from
high to low (see Figure 9).
Pulse-width distortion (PWD) results when t
differ in value. PWD is defined as the difference between
t
between t
mum 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 transmitted.
Typically, PWD on the order of 20-30% of the minimum
pulse width is tolerable; the exact figure depends on the
particular application (RS232, RS422, T-1, etc.).
Propagation delay skew, t
to consider in parallel data applications where synchroni-
zation of signals on parallel data lines is a concern.
If the parallel data is being sent through a group of opto-
couplers, differences in propagation delays will cause the
data to arrive at the outputs of the optocouplers at differ-
ent times. If this difference in propagation delays is large
enough, it will determine the maximum rate at which par-
allel data can be sent through the optocouplers.
Propagation delay skew is defined as the difference be-
tween the minimum and maximum propagation delays,
I
I
10
Figure 9. Propagation delay and skew waveform
O
O
F
F
PLH
and t
PHL
PLH
and often PWD is defined as the difference
and t
50%
50%
CMOS
50%,
PHL
and often determines the maxi-
PSK
, is an important parameter
t
PSK
PLH
50%,
CMOS
) is the amount
PLH
and t
PHL
PHL
) is
INPUTS
OUTPUTS
either t
which are operating under the same conditions (i.e., the
same supply voltage, output load, and operating temper-
ature). As illustrated in Figure 10, if the inputs of a group of
optocouplers are switched either ON or OFF at the same
time, t
tion delay, either t
delay, either t
termine the maximum parallel data transmission rate.
Figure 10 is the timing diagram of a typical parallel data
application with both the clock and the data lines being
sent through optocouplers. The figure shows data and
clock signals at the inputs and outputs of the optocou-
plers. 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 opt-
ocoupler. Figure 10 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 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 optocouplers in a parallel
application is twice t
slightly longer pulse width to ensure that any additional
uncertainty in the rest of the circuit does not cause a
problem.
Figure 10. Parallel data transmission example
CLOCK
CLOCK
DATA
DATA
PSK
PLH
is the difference between the shortest propaga-
or t
PLH
t
PHL
PSK
or t
PLH
, for any given group of optocouplers
PHL
PSK
or t
. As mentioned earlier, t
. A cautious design should use a
t
PHL
PSK
, and the longest propagation
PSK
can de-