HD26LS31 Datasheet, PDF (12/15 Pages) Hitachi Semiconductor – Quadruple Differential Line Drivers With 3 State Outputs

HD26LS31
A feature of termination implemented as shown in figure 9 is that power dissipation is low when the duty of
the transmitted signal is high.
However, care is required, since if R_T is sufficiently small, when the output on the pulled-up side goes low,
since the inverter transistor (Q₄ in figure 2) has no protection circuit, and so a large current will flow and
the output low level will rise.
Figure 10 shows the output voltage characteristics when termination resistance R_T is varied.
With the method of using the driver described above, if termination resistance R_T becomes sufficiently
small, the region within which the output current limiter circuit operates will be entered, as can be seen
from the I_OH vs. V_OH characteristics shown in figure 3. In this region, the output stage power dissipation is
large and the output voltage changes abruptly. A measure such as insertion of a capacitor in series with the
termination resistance is therefore necessary. Consequently, when selecting the transmission line, the
circuit termination resistance to be used requires careful consideration.
5
V_{OH (Y)}
2
1.0
0.5
V_CC = 5 V
Y
Ta = 25°C
0.2
V_{OL (Z)}
"H"
0.1
Z
0.05
10 20 50 100 200 500 1 k 2 k 5 k 10 k 20 k 50 k
Termination Resistance R_T (Ω)
R_T
GND
V_OH
V_OL
Figure 8 Termination Resistance vs. Output Voltage Characteristics
Data input
V_CC
Y
R_T
Z
R_T
Figure 9 Example of Driver Use-3
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