SN75ALS085
LAN ACCESS UNIT INTERFACE DUAL DRIVER/RECEIVER
SLLS054D – APRIL 1989 – REVISED OCTOBER 2001
DW OR NT PACKAGE
Meets or Exceeds the Requirements of IOS
8802.3:1989 and ANSI/IEEE Std 802.3-1988
(TOP VIEW)
Interdevice Loopback Paths for System
Testing
TXI1
TXEN1
LOOP1
GND
TXO1
TXO1
1
24
23
22
21
20
2
Squelch Function Implemented on the
Receiver Inputs
V
3
CC
RXI1
RXI1
4
RXEN1
RXO1
RXO2
RXEN2
GND
5
Drives a Balanced 78-Ω Load
6
19 GND
Transformer Coupling Not Required in
System
7
18
17
16
15
14
13
GND
RXI2
RXI2
8
Power-Up/Power-Down Protection (Glitch
Free)
9
10
11
12
LOOP2
TXEN2
TXI2
V
CC
Isolated Ground Pins for Reduced Noise
Coupling
TXO2
TXO2
Fault-Condition Protection Built Into the
Device
Driver Inputs Are Level-Shifted ECL
Compatible
Package Options Include Plastic
Small-Outline (DW) Package and Standard
Plastic (NT) DIP
description
The SN75ALS085 is a high-speed, advanced low-power Schottky, dual-channel driver/receiver device
designed for use in the AUI of ANSI/IEEE Std 802.3-1988. The two drivers on the device drive a 78-Ω balanced,
terminated twisted-pair transmission line up to a maximum length of 50 meters. In the off (idle) state, the drivers
maintain minimal differential output voltage on the twisted-pair line and, at the same time, remain within the
required output common-mode range.
With the driver enable (TXEN) high, upon receiving the first falling edge into the driver input, the differential
outputs rise to full-amplitude output levels within 25 ns. The output amplitude is maintained for the remainder
of the packet. After the last positive packet edge is transmitted into the driver, the driver maintains a minimum
of 70% full differential output for a minimum of 200 ns, then decays to a minimum level for the reset (idle)
condition within 8 µs. Disabling the driver by taking the driver enable low also forces the output into the idle
conditionafterthenormal8-µstimeout. Whileoperating, thedriversareabletowithstandasetoffaultconditions
and not suffer damage due to the faults being applied. The drivers power up in the idle state to ensure that no
activity is placed on the twisted-pair cable, which could be interpreted as network traffic.
The line receiver squelch function interfaces to a differential twisted-pair line terminated external to the device.
The receiver squelch circuit allows differential receive signals to pass through, as long as the input amplitude
and pulse duration are greater than the minimum squelch threshold. This ensures a good signal-to-noise ratio
while the data path is active and prevents system noise from causing false data transitions during line shutdown
and line-idle conditions. The receiver outputs (RXO) default to a high level and the receiver-enable (RXEN)
outputs default to a low level while the squelch function is blocking the data path through the receiver (idle). The
linereceiversquelchbecomesactivewithin50nswhentheinputsquelchthresholdisexceeded. RXENisdriven
high when the squelch circuit allows data to pass through the receiver. The receiver squelch circuit also can
withstand a set of fault conditions while operating, without causing permanent damage to the device.
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
Copyright 2001, Texas Instruments Incorporated
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
1
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