Datasheet

SCEA022
7–264
Achieving Maximum Speed on Parallel Buses With Gunning Transceiver Logic (GTLP)
3.1.2 Propagation Time Due to Simultaneous Switching
The simultaneous switching parameter, ∆t
pd
, is the difference in propagation time that arises
from the simultaneous switching of several outputs of the same device.
Data sheets show only the maximum propagation time of one output when it is the only one to
be switched. An additional propagation time must be taken into account when multiple outputs
are switched simultaneously. The reason for the increase in propagation time is the internal
package inductance, which works as a current brake. The more outputs that are switched on,
the greater the current and, therefore, the braking effect is greater. Figure 7 shows this
correlation for different package options.
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0 1 2 3 4 5 6 7 8 9 1011121314 15161718 1920 2122232425262728293031
∆ t
pd
– ns
Number of Outputs Switching
SSOP 48 Pin
Trend SSOP 48 Pin
TSSOP 48 Pin
Trend TSSOP 48 Pin
TVSOP 48 Pin
Trend TVSOP 48 Pin
LFBGA 96 Ball
Trend LFBGA 96 Ball
Figure 7. Effect of Simultaneous Switching on Propagation Time
The low-profile fine-pitch BGA (LFBGA) package shows the best skew behavior, when forced by
simultaneous switching, in this comparison. Despite having double the number of outputs
switched at the same time, the absolute difference of the propagation delay in Figure 7 is not
significantly greater than that of other modern 16-bit dual-inline packages.