DC89C386 Datasheet, PDF (7/10 Pages) National Semiconductor (TI) – Twelve Channel CMOS Differential Line Receiver

Application Information (Continued)
V2 are less likely to be equal to the crossing point voltage.
Thus, the differential propagation delays will not be mea-
sured from zero volts on the differential waveform.
The differential skew also provides information about the
pulse width distortion of the output waveform relative to the
differential input waveform. The higher the skew, the greater
the distortion of the output waveform. Assuming the differen-
tial input has a 50% duty cycle, the output will have a 50%
duty cycle if skew equals zero and less than a 50% duty
cycle if skew is greater than zero.
Only t_SK is specified in this datasheet for the DS89C386. t_SK
is measured singIe-endedly but corresponds to differential
skew. Because, for single-ended skew, when V_REF equals
V1 and V2, t_PHL equals t_PHLD when t_PHLD is measured from
the crossing point.
More information can be calculated from the propagation
delays. The channel to channel and device to device skew
may be calculated in addition to the types of skew mentioned
previously. These parameters provide timing performance
information beneficial when designing. The channel to chan-
nel skew is calculated from the variation in propagation delay
from receiver to receiver within one package. The device to
device skew is calculated from the variation in propagation
delay from one DS89C386 to another DS89C386.
For the DS89C386, the maximum channel to channel skew
is 20 ns (t_p max — t_p min) where t_p is the low to high or high
Typical Performance Characteristics
to low propagation delay. The minimum channel to channel
skew is 0 ns since it is possible for all 12 receivers to have
identical propagation delays. Note, this is best and worst
case calculations used whenever t_SK (channel) is not inde-
pendently characterized and specified in the datasheet. The
device to device skew may be calculated in the same way
and the results are identical. Therefore, the device to device
skew is 20 ns and 0 ns maximum and minimum respectively.
TABLE 1. DS89C386 Skew Table
Parameter
t_SK (diff.)
t_SK (channel)
t_SK (device)
Min Typ Max Units
0
2
4
ns
0
20
ns
0
20
ns
Note t_SK (diff.) in Table 1 is the same as t_SK in the datasheet.
Also, t_SK (channel) and t_SK (device) are calculations, but are
guaranteed by the propagation delay tests. Both t_SK (chan-
nel) and t_SK (device) would normally be tighter whenever
specified from characterization data.
The information in this section of the datasheet is to help
clarify how skew is defined in this datasheet. This should
help when designing the DS89C386 into most applications.
Receiver Input Voltage vs
Receiver Input Current
(Notes 6, 7)
01208514
Note 6: The DS89C386 is V.11 compatible. I_IN (RI input) is not ≥ 0 when V_IN= 3V due to internal failsafe bias resistors (see Figure 6). See ITU V.11 for complete
conditions.
Note 7: Failsafe (open inputs) is maintained over entire common mode range and operating range ±10V.
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