DS89C387_16 Datasheet, PDF (8/15 Pages) Texas Instruments – Twelve Channel CMOS Differential Line Driver

DS89C387
SNLS101E – MAY 1995 – REVISED APRIL 2013
www.ti.com
Figure 15. Waveforms for Circuit 4 – Waveforms for Circuit 4 (See Figure 14)
Complementary skew is calculated from single-ended propagation delay measurements on complementary
output signals, DO and DO*. Note, when V3 and V4 are absolute values, they are identical on DO and DO*; but
vary whenever they are relative values.
The complementary skew reveals information about the contour of the rising and falling edge of the differential
output signal of the driver. This is important information because the receiver will interpret the differential output
signal. If the differential transitions do not continuously ascend or decend through the receivers threshold region,
errors may occur. Errors may also occur if the transitions are too slow.
In addition, complementary skew provides information about the common mode modulation of the driver. The
common mode voltage is represented by (DO–DO*)/2. This information may be used as a means for determining
EMI affects.
Only “Skew” is specified in this datasheet for the DS89C387. It refers to the complementary skew of the driver.
Complementary skew is measured at both V3 and V4 (see Figure 15).
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 channel 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 DS89C387 to another DS89C387.
For the DS89C387, the maximum channel to channel skew is 9 ns (t_p max–t_p min) where t_p is the low to high or
high to low propagation delay. The minimum channel to channel skew is 0 ns since it is possible for all 12 drivers
to have identical propagation delays. Note, this is best and worst case calculations used whenever Skew
(channel) is not independently characterized and specified in the datasheet. The device to device skew may be
calculated in the same way and the results are the same. Therefore, the device to device skew is 9 ns and 0 ns
maximum and minimum respectively.
Skew (comp.)
Skew (channel)
Skew (device)
Parameter
Table 1. DS89C387 Skew Table
Min
Typ
Max
0
0.5
3
0
9
0
9
Units
ns
ns
ns
Note Skew (comp.) in Table 1 is the same as “Skew” in the datasheet. Also Skew (channel) and Skew (device)
are calculations, but are specified by the propagation delay tests. Both Skew (channel) and Skew (device) would
normally be tighter whenever specified from characterization data.
The information in this section of the datasheet is to help clarity how skew is defined in this datasheet. This
should help when designing the DS89C387 into most applications.
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