am26ls30fn Freescale Semiconductor, Inc, am26ls30fn Datasheet - Page 10

• Manufacturer Part Number: am26ls30fn
• Description: Dual Differential/ Quad Single.ended Line Drivers
• Manufacturer: Freescale Semiconductor, Inc

Differential System
Figure 17. Although EIA–422–A does not specifically address
multiple driver situations, the AM26LS30 can be used in this
manner since the outputs can be put into a high impedance
mode. It is, however, the system designer’s responsibility to
ensure the Enable pins are properly controlled so as to
prevent two drivers on the same cable from being “on” at the
same time.
may be connected on one system is determined by the input
current of each receiver, the maximum leakage current of
each “off” driver, and the DC current through each
terminating resistor. The sum of these currents must not
exceed the capability of the “on” driver ( 60 mA). If the cable
is of any significant length, with receivers at various points
along its length, the common mode voltage may vary along
its length, and this parameter must be considered when
calculating the maximum driver current.
characteristics and the data rate, but also by the DC
resistance. The maximum resistance must be such that the
minimum voltage across any receiver inputs is never less than
200 mV.
17 must be connected together by a dedicated wire (or the
shield) in the cable to provide a common reference. Chassis
grounds or power line grounds should not be relied on for this
common connection as they may generate significant
common mode differences. Additionally, they usually do not
provide a sufficiently low impedance at the frequencies
of interest.
Single–Ended System
Figure 18. Multiple drivers on a single data line are not
possible since the drivers cannot be put into a high
impedance mode. Although each driver is shown connected
to a single receiver, multiple receivers can be driven from a
single driver as long as the total load current of the receivers
and the terminating resistor does not exceed the capability of
the driver ( 60 mA). If the cable is of any significant length,
with receivers at various points along its length, the common
mode voltage may vary along its length, and this parameter
must be considered when calculating the maximum
driver current.
characteristics and the data rate, but also by the DC
resistance. The maximum resistance must be such that the
10
An example of a typical EIA–422–A system is shown in
The limit on the number of receivers and drivers which
The cable requirements are defined not only by the AC
The ground terminals of each driver and receiver in Figure
An example of a typical EIA–423–A system is shown in
The cable requirements are defined not only by the AC
(Pin numbers refer to DIP and SO–16 packages only.)
SYSTEM EXAMPLES
AM26LS30
minimum voltage across any receiver inputs is never less
than 200 mV.
18 must be connected together by a dedicated wire (or the
shield) in the cable so as to provide a common reference.
Chassis grounds or power line grounds should not be relied
on for this common connection as they may generate
significant common mode differences. Additionally, they
usually do not provide a sufficiently low impedance at the
frequencies of interest.
Additional Modes of Operation
not required in a particular application, the AM26LS30 can be
operated in two other modes.
(Pin 4 = 0) with V EE connected to any voltage between
ground and –5.25 V. Outputs in the low state will be
referenced to V EE , resulting in a differential output voltage
greater than that shown in Figure 6. The Enable pins will
operate the same as previously described.
(Pin 4 = 1) with V EE connected to any voltage between
ground and –5.25 V. Outputs in the high state will be at a
voltage as shown in Figure 10, while outputs in a low state
will be referenced to V EE .
Termination Resistors
the shape and integrity of a waveform traveling along a cable,
the cable must be terminated in an impedance equal to its
characteristic impedance. In a system such as that depicted
in Figure 17, in which data can travel in both directions, both
physical ends of the cable must be terminated. Stubs leading
to each receiver and driver should be as short as possible.
data normally travels in one direction only, a terminator is
theoretically required only at the receiving end of the cable.
However, if the cable is in a location where noise spikes of
several volts can be induced onto it, then a terminator
(preferably a series resistor) should be placed at the driver
end to prevent damage to the driver.
reflections which can have amplitudes of several volts above
V CC or several volts below ground or V EE . These
overshoots/undershoots can disrupt the driver and/or
receiver, create false data, and in some cases, damage
components on the bus.
The ground terminals of each driver and receiver in Figure
If compliance with EIA–422–A or EIA–423–A Standard is
1) The device may be operated in the differential mode
2) The device may be operated in the single–ended mode
Transmission line theory states that, in order to preserve
In a system such as that depicted in Figure 18, in which
Leaving off the terminations will generally result in
MOTOROLA ANALOG IC DEVICE DATA