HCPL-261A Datasheet, PDF (15/16 Pages) Agilent(Hewlett-Packard) – HCMOS Compatible, High CMR, 10 MBd Optocouplers

V_CC
74HC00
(OR ANY
OPEN-COLLECTOR/
OPEN-DRAIN
LOGIC GATE)
820 Ω
HCPL-261X
1
2
LED
3
4
V_CC
74HC04
(OR ANY
TOTEM-POLE
OUTPUT LOGIC
GATE)
1N4148
750 Ω
HCPL-261A/261N
1
2
LED
3
4
Figure 23. TTL Open-Collector/Open Drain Gate Drive Circuit
for HCPL-261A/-261N Families.
Figure 24. CMOS Gate Drive Circuit for HCPL-261A/-
261N Families.
Table 1. Effects of Common Mode Pulse Direction on Transient I_LED
If dV_CM/dt Is:
positive (>0)
negative (<0)
then I_LP Flows:
away from LED
anode through C_LA
toward LED
and I_LN Flows:
away from LED
cathode through C_LC
toward LED
If |I_LP| < |I_LN|,
LED I_F Current
Is Momentarily:
increased
decreased
If |I_LP| > |I_LN|,
LED I_F Current
Is Momentarily:
decreased
increased
anode through C_LA cathode through C_LC
Propagation Delay, Pulse-
Width Distortion and
Propagation Delay Skew
Propagation delay is a figure of
merit which describes how
quickly a logic signal propagates
through a system. The propaga-
tion delay from low to high (t_PLH)
is the amount 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_PHL) is the
amount of time required for the
input signal to propagate to the
output, causing the output to
change from high to low (see
Figure 9).
Pulse-width distortion (PWD)
results when t_PLH and t_PHL differ
in value. PWD is defined as the
difference between t_PLH and t_PHL
and often determines the
maximum 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 appli-
cation (RS232, RS422, T-1, etc.).
Propagation delay skew, t_PSK, is
an important parameter to con-
sider in parallel data applications
where synchronization of signals
on parallel data lines is a con-
cern. If the parallel data is being
sent through a group of opto-
couplers, differences in propaga-
tion delays will cause the data to
arrive at the outputs of the opto-
couplers 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
optocouplers.
Propagation delay skew is defined
as the difference between the
minimum and maximum propaga-
tion delays, either t_PLH or t_PHL, for
any given group of optocouplers
which are operating under the
same conditions (i.e., the same
drive current, supply voltage,
output load, and operating
temperature). As illustrated in
Figure 25, if the inputs of a group
of optocouplers are switched
either ON or OFF at the same
time, t_PSK is the difference
between the shortest propagation
delay, either t_PLH or t_PHL, and the
longest propagation delay, either
t_PLH or t_PHL.
As mentioned earlier, t_PSK can
determine the maximum parallel
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