HD26LS31 datasheet(7/12 Pages) RENESAS

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HD26LS31

Rev.2.00, Jul.16.2004, page 7 of 11

HD26LS31 Line Driver Applications

The HD26LS31 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

• Three-state output

• On-chip current limiter circuit

• Sink current and source current both 40 mA

A block diagram is shown in figure 1. 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.

Input is TTL compatible, and an output current limiter circuit is built into the output stage as shown in figure 2.

Enable G

Figure 1 HD26LS31 Block Diagram

The output current limiter circuit consists of transistor Q

1 and resistance R1, and operates when the voltage drop on both

sides of R

1 reaches approximately 0.7 V. At this time the current, i, is as follows:

i = 0.7 (V) / 9 (

Ω)≈ 78 (mA)

When a current greater than this flows, Q

1 is turned on, the Q2 base current flows to the output side, and the flow of an

excessively large output current is prevented.

However, since this type of current limiter circuit has the characteristics shown in figure 3, the output stage power

dissipation is large.

Therefore, when the output is shorted, this should be limited to a maximum of one second for one pin only.

The I

OL vs. VOL characteristic for low-level output is shown in figure 4.

An example of termination resistance connection when the HD26LS31 is used as a balanced differential type driver is

shown.

VCC

Output

Ω

Figure 2 Output Stage Circuit Configuration

HD26LS31 Datasheet(PDF) 7 Page - Renesas Technology Corp