HD26C31 Datasheet, PDF (9/12 Pages) Hitachi Semiconductor – Quadruple Differential Line Drivers With 3 State Outputs

HD26C31
Figure 5 shows the output voltage characteristic when termination resistance R_T is varied.
Also, when used in a party line system, etc., the low level rises further due to the receiver input bias current, so that it is
probably advisable to drop the termination resistance to GND.
However, the fact that it is possible to make the value of R_T equal to the characteristic impedance of the transmission
line offers the advantage of being able to hold the power dissipation on the side outputting a high level to a lower level
than in the above case.
Consequently, the appropriate use must be decided according to the actual operating conditions (transmission line
characteristics, transmission distance, whether a party line is used, etc.).
Figure 6 shows the output characteristics when termination resistance R_T is varied.
I_OH
Y "H"
R_T
"L"
Z
I_OL I_IN (Receiver)
Figure 3 Example of Driver Use-1
I_OH
Y "H"
R_T
"L" ^RT
Z
I_IN (Receiver)
Figure 4 Example of Driver Use-2
Output Voltage vs. Termination Resistance
10
V_OH(Y)
1
Y
R_T
0.1
"H"
R_T
V_OH
0.01
Z
0.001
10 20
V_OL(Z)
50 100 200 500 1k 2k 5k 10k 20k 50k
Termination Resistance R_T (Ω)
V_OL
GND
Figure 5 Termination Resistance vs. Output Voltage Characteristics
A feature of termination implemented as shown in figure 7 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 high, a large
current will flow and the output low level will rise.
Figure 8 shows the output characteristics when termination resistance R_T is varied.
Rev.2.00, Jul.16.2004, page 9 of 11