HD26LS32 Datasheet, PDF (8/15 Pages) Hitachi Semiconductor – Quadruple Differential Line Receivers With 3 State Outputs

HD26LS32
HD26LS32 Line Receiver Applications
The HD26LS32 is a line receiver that meets the EIA RS-422A and RS-423A conditions. It has a high in-
phase input voltage range, both positive and negative, enabling highly reliable transmission to be
performed even in noisy environments.
Its main features are listed below.
• Operates on a single 5 V power supply.
• Three-state output
• On-chip fail-safe circuit
• ±7 V in-phase input voltage range
• ±200 mV input sensitivity
• Minimum 6 k input resistance
A block diagram is shown in figure 1. The enable function is common to all four drivers, and either active-
high or active-low input can be selected.
When exchange is carried out using a party line system, it is better to keep the receiver input bias current
constituting the driver load small, as this allows more receivers to be connected.
Consequently, whereas an input resistance of 4 k or above is stipulated in RS-422A and RS-423A, the
HD26LS32 has been designed to allow a greater margin, with a minimum resistance of 6 k .
Figure 2 shows the input current characteristics of the HD26LS32.
The shaded areas in the graph indicate the input current allowable range stipulated in RS-422A and RS-
423A.
HD26LS32 output is LS-TTL compatible and has a three-state function, enabling the output to be placed in
the high-impedance state, and so making the device suitable for bus line type applications.
With an in-phase input voltage range of ±7 V and a ±200 mV input sensitivity, the HD26LS32 can
withstand use in noisy environments.
Also, since signals sent over a long-distance transmission line require a long transition time, it also takes a
long time to cross the receiver’s input threshold level.
Therefore, the input is provided with hysteresis of around 30 mV to prevent receiver output misoperation
due to noise.
An example of input hysteresis is shown in figure 3.
The fail-safe function consists of resistances R connecting input A to V_CC and input B to GND, as shown in
figure 4.
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