DS8935WM National Semiconductor, DS8935WM Datasheet - Page 9

• Manufacturer Part Number: DS8935WM
• Description: IC LOCAL TALK W/TRI-STATE SO20
• Manufacturer: National Semiconductor
• Type: Transceiverr

Specifications of DS8935WM

• Number Of Drivers/receivers: 2/3
• Protocol: RS422, RS423
• Voltage - Supply: 4.75 V ~ 5.25 V
• Mounting Type: Surface Mount
• Package / Case: *
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *DS8935WM

Typical Application Information
UNUSED PINS
Unused driver outputs should be left open. If tied to either
ground or supply, the driver may enter an I
sume excessive power. Unused driver inputs should not be
left floating as this may lead to unwanted switching which
may affect I
used driver inputs should be tied to ground.
Receiver outputs will be in a HIGH state when inputs are
open; therefore, outputs should not be tied to ground. It is
best to leave unused receiver outputs floating.
RECEIVER FAILSAFE
All three receivers on this device incorporate open input fail-
safe protection. The differential receiver output will be in a
HIGH state when inputs are open, but will be indetermined if
inputs are shorted together. Unused differential inputs
should be left floating.
Both single-ended receivers (inverting and non-inverting) are
biased internally so that an open input will result in a HIGH
output. Therefore, these inputs should not be shorted to
ground when unused.
BYPASS CAPACITORS
Bypass capacitors are recommended for both V
Noise induced on the supply lines can affect the signal qual-
ity of the output; V
V
value of 0.1 µF is typically used.
SINGLE +5V SUPPLY
The DS8935 is derived from the DS3691/92 which could be
configured using a single +5V supply (V
is not specified for this type of operation. However, the de-
vice will not be damaged if operated using a single +5V sup-
ply.
Both drivers require the −5V supply in order to meet the out-
put voltage levels specified. When the device switches from
a positive voltage to the complimentary state, it is pulled to-
ward the V
(Continued)
OL
. Capacitors help reduce the effect on signal quality. A
EE
CC
level. If that level is 0V, then the complimentary
, particularly the frequency component. Un-
FIGURE 14. Differential Communication, Transformer-Coupled to a Twisted-Pair Line
CC
affects the V
OH
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and V
= 0V). This device
OS
state and con-
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CC
affects the
and V
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.
9
Since this is a power device, it is recommended to use a by-
pass capacitor for each supply and for each device. Sharing
a bypass capacitor between other devices may not be suffi-
cient.
TERMINATION
On a multi-point transmission line which is electrically long, it
is advisable to terminate the line at both ends with its charac-
teristic impedance to prevent signal reflection and its associ-
ated noise/crosstalk.
A 100
EIA-422 for differential signals. The DS8935 is also specified
using 140
ciated with the driver output. The additional resistance is
typical of applications requiring EMI filtering on the driver
outputs.
TWO-WIRE LocalTalk
The DS8935 is a single chip solution for a LocalTalk inter-
face. A typical application is shown in Figure 12 .
An alternative implementation of LocalTalk is to only use two
wires to communicate. The differential data lines can be
transformer-coupled on to a twisted pair medium. See Figure
14 . The handshake function must then be accomplished in
software.
state will be near 0V instead of V
switch from about 4V to 0V, instead of 4V to −4V. The differ-
ential driver will meet TIA/EIA-422, but with a reduced noise
margin. The single-ended driver will not meet TIA/EIA-423
without the −5V supply.
The receivers will be functional but may suffer parametri-
cally. The inverting receiver is referenced to V
the threshold may shift slightly. The inputs can still vary over
the
±
10V common mode range.
termination resistor is commonly specified by TIA/
termination which will result in less power asso-
EE
DS012066-17
. Thus, the output would
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therefore,