HD26C31 Datasheet, PDF (8/12 Pages) Hitachi Semiconductor – Quadruple Differential Line Drivers With 3 State Outputs

HD26C31
HD26C31 Line Driver Applications
The HD26C31 is a line driver that meets the EIA RS-422A conditions, and has been designed to supply a high current
for differential signals to a bus line. Its features are listed below.
• Operates on a single 5 V power supply.
• High output impedance when power is off
• Sink current and source current both 20 mA
• On-chip power up/down protection circuit
As shown by the logic diagram, the enable function is common to all four drivers, and either active-high or active-low
can be selected.
The output section consists of two output stages (the Y side and Z side), each of which has the same sink current and
source current capacity.
Connection of a termination resistance when the HD26C31 is used as a balanced differential type driver is shown.
Output Characteristics ("H" Level)
5.0
Ta = 25°C
4.0
V_CC = 5.5 V
3.0
V_CC = 5.0 V
2.0
1.0
V_CC = 4.5 V
0
–20 –40 –60 –80 –100
Output Current I_OH (mA)
Figure 1 I_OH vs. V_OH Characteristics
Output Characteristics ("L" Level)
0.5
Ta = 25°C
0.4
V_CC = 4.5 V
0.3
V_CC = 5.0 V
0.2
V_CC = 5.5 V
0.1
0
20 40 60 80 100
Output Current I_OL (mA)
Figure 2 I_OL vs. V_OL Characteristics
When termination resistance R_T is connected between the two transmission lines, as shown in figure 3 the current path
situation is that current I_OH on the side outputting a high level (in this case, the Y output) flows to the side outputting a
low level (in this case, the Z output) via R_T, with the result that the low level rise is large.
If termination resistance R_T is dropped to GND on both transmit lines, as shown in figure 4 the current path situation is
that the current that flows into the side outputting a low level (in this case, the Z output) is only the input bias current
from the receiver. As this input bias current is small compared with the signal current, it has almost no effect on the
differential input signal at the receiver end.
Rev.2.00, Jul.16.2004, page 8 of 11