5V, Low Power, High Speed or Slew Rate
Limited, RS-485/RS-422 Transceivers
The Intersil RS-485/RS-422 devices are BiCMOS 5V
powered, single transceivers that meet both the RS-485 and
RS-422 standards for balanced communication. Unlike
competitive devices, this Intersil family is specified for 10%
tolerance supplies (4.5V to 5.5V).
The ISL8483, ISL8488, and ISL8489 utilize slew rate limited
drivers which reduce EMI, and minimize reflections from
improperly terminated transmission lines, or unterminated
stubs in multidrop and multipoint applications.
Data rates up to 5Mbps are achievable by using the
ISL8485, ISL8490, or ISL8491, which feature higher slew
rates.
All devices present a “single unit load” to the RS-485 bus,
which allows up to 32 transceivers on the network.
Receiver (Rx) inputs feature a “fail-safe if open” design,
which ensures a logic high Rx output if Rx inputs are
floating.
Driver (Tx) outputs are short circuit protected, even for
voltages exceeding the power supply voltage. Additionally,
on-chip thermal shutdown circuitry disables the Tx outputs to
prevent damage if power dissipation becomes excessive.
The ISL8488 - 91 are configured for full duplex (separate Rx
input and Tx output pins) applications. The ISL8488 and
ISL8490 are offered in space saving 8 lead packages for
applications not requiring Rx and Tx output disable functions
(e.g., point-to-point). Half duplex configurations (ISL8483,
ISL8485) multiplex the Rx inputs and Tx outputs to allow
transceivers with Rx and Tx disable functions in 8 lead
packages.
FN6046.3
Features
• Specified for 10% Tolerance Supplies
• Class 3 ESD Protection (HBM) on all Pins. . . . . . . . >7kV
• High Data Rates. . . . . . . . . . . . . . . . . . . . . . up to 5Mbps
• Slew Rate Limited Versions for Error Free Data
Transmission at 250kbps (ISL8483, ISL8488, ISL8489)
• Single Unit Load Allows up to 32 Devices on the Bus
• 1nA Low Current Shutdown Mode (ISL8483)
• Low Quiescent Current:
µA (ISL8483, ISL8488, ISL8489)
-160
µA (ISL8485, ISL8490, ISL8491)
-340
• -7V to +12V Common Mode Input Voltage Range
• Three State Rx and Tx Outputs (Except ISL8488,
ISL8490)
CAUTION: Stresses above those listed in “Absolute Maximum Ratings” may cause permanent damage to the device. This is a stress only rating and operation of the
device at these or any other conditions above those indicated in the operational sections of this specification is not implied.
NOTE:
is measured with the component mounted on a low effective thermal conductivity test board in free air. See Tech Brief TB379 for details.
1. θ
JA
o
C to 70oC
o
C to 85oC
θ
(oC/W)
JA
o
C to 150oC
o
o
C
C
Electrical SpecificationsTest Conditions: V
Typicals are at V
PARAMETERSYMBOLTEST CONDITIONS
DC CHARACTERISTICS
Driver Differential V
Driver Differential V
Change in Magnitude of Driver
Differential V
OUT
Complementary Output States
Driver Common-Mode V
Change in Magnitude of Driver
Driver Input to Output Delayt
Driver Output Skewt
Driver Differential Rise or Fall Timet
Driver Enable to Output Hight
Driver Enable to Output Lowt
Driver Disable from Output Hight
Driver Disable from Output Lowt
Receiver Input to Output Delayt
Receiver Skew | t
PLH
- t
|t
PHL
Receiver Enable to Output Hight
Receiver Enable to Output Lowt
Receiver Disable from Output Hight
Receiver Disable from Output Lowt
Maximum Data Ratef
Driver Input to Output Delayt
Driver Output Skewt
Driver Differential Rise or Fall Timet
Driver Enable to Output Hight
Driver Enable to Output Lowt
Driver Disable from Output Hight
Driver Disable from Output Lowt
Receiver Input to Output Delayt
- t
Receiver Skew | t
PLH
|t
PHL
Receiver Enable to Output Hight
Receiver Enable to Output Lowt
Receiver Disable from Output Hight
2. All currents into device pins are positive; all currents out of device pins are negative. All voltages are referenced to device ground unless
otherwise specified.
3. Supply current specification is valid for loaded drivers when DE = 0V.
4. Applies to peak current. See “Typical Performance Curves” for more information.
5. When testing the ISL8483, keep RE
6. When testing the ISL8483, the RE
7. The ISL8483 is put into shutdown by bringing RE
= 0 to prevent the device from entering SHDN.
signal high time must be short enough (typically <200ns) to prevent the device from entering SHDN.
high and DE low. If the inputs are in this state for less than 50ns, the parts are guaranteed not
to enter shutdown. If the inputs are in this state for at least 600ns, the parts are guaranteed to have entered shutdown. See “Low-Power
Shutdown Mode” section.
8. Keep RE
9. Set the RE
= VCC, and set the DE signal low time >600ns to ensure that the device enters SHDN.
signal high time >600ns to ensure that the device enters SHDN.
10. Devices meeting these limits are denoted as “single unit load (1 UL)” transceivers. The RS-485 standard allows up to 32 Unit Loads on the bus.
FIGURE 5. RECEIVER ENABLE AND DISABLE TIMES (EXCLUDING ISL8488, ISL8490)
1kΩ
SW
15pF
V
GND
CC
CC
CC
CC
NOTE 7
RE
tZH, t
ZH(SHDN)
NOTE 7
RO
t
, t
ZL
ZL(SHDN)
NOTE 7
RO
FIGURE 5B. MEASUREMENT POINTS
OUTPUT HIGH
1.5V
1.5V
OUTPUT LOW
1.5V1.5V
t
HZ
t
LZ
3V
0V
VOH - 0.5V
VOL + 0.5V
V
OH
0V
V
CC
V
OL
Application Information
RS-485 and RS-422 are differential (balanced) data
transmission standards for use in long haul or noisy
environments. RS-422 is a subset of RS-485, so RS-485
transceivers are also RS-422 compliant. RS-422 is a pointto-multipoint (multidrop) standard, which allows only one
driver and up to 10 (assuming one unit load devices)
receivers on each bus. RS-485 is a true multipoint standard,
which allows up to 32 one unit load devices (any
combination of drivers and receivers) on each bus. To allow
for multipoint operation, the RS-485 spec requires that
drivers must handle bus contention without sustaining any
damage.
Another important advantage of RS-485 is the extended
common mode range (CMR), which specifies that the driver
outputs and receiver inputs withstand signals that range
from +12V to -7V. RS-422 and RS-485 are intended for runs
as long as 4000’, so the wide CMR is necessary to handle
ground potential differences, as well as voltages induced in
the cable by external fields.
Receiver Features
These devices utilize a differential input receiver for maximum
noise immunity and common mode rejection. Input sensitivi ty
is ±200mV, as required by the RS422 and RS-485
specifications.
Receiver input impedance surpasses the RS-422 spec of
4kΩ, and meets the RS-485 “Unit Load” requirement of
12kΩ minimum.
Receiver inputs function with common mode voltages as
great as ±7V outside the power supplies (i.e., +12V and
-7V), making them ideal for long networks where induced
voltages are a realistic concern.
All the receivers include a “fail-safe if open” function that
guarantees a high level receiver output if the receiver inputs
are unconnected (floating).
Receivers easily meet the data rates supported by the
corresponding driver.
ISL8483/85/89/91 receiver outputs are three-statable via the
active low RE
input.
Driver Features
The RS-485/422 driver is a differential output device that
delivers at least 1.5Vacross a 54Ω load (RS-485), and at
least 2V across a 100Ω load (RS-422). The drivers feature
low propagation delay skew to maximize bit width, and to
minimize EMI.
Drivers of the ISL8483/85/89/91 are three-statable via the
active high DE input.
The ISL8483/88/89 driver outputs are slew rate limited to
minimize EMI, and to minimize reflections in unterminated or
improperly terminated networks. Data rate on these slew
rate limited versions is a maximum of 250kbps. Outputs of
ISL8485/90/91 drivers are not limited, so faster output
transition times allow data rates of at least 5Mbps.
Data Rate, Cables, and Terminations
RS-485/422 are intended for network lengths up to 4000’,
but the maximum system data rate decreases as the
transmission length increases. Devices operating at 5Mbps
are limited to lengths less than 100’, while the 250kbps
versions can operate at full data rates with lengths in excess
of 1000’.
Twisted pair is the cable of choice for RS-485/422 networks.
Twisted pair cables tend to pick up noise and other
electromagnetically induced voltages as common mode
signals, which are effectively rejected by the differential
receivers in these ICs.
Proper termination is imperative, when using the 5Mbps
devices, to minimize reflections. Short networks using the
250kbps versions need not be terminated, but, terminations
are recommended unless power dissipation is an overriding
concern.
In point-to-point, or point-to-multipoint (single driver on bus)
networks, the main cable should be terminated in its
characteristic impedance (typically 120Ω) at the end farthest
from the driver. In multi-receiver applications, stubs
connecting receivers to the main cable should be kept as
short as possible. Multipoint (multi-driver) systems require
that the main cable be terminated in its characteristic
impedance at both ends. Stubs connecting a transceiver to
the main cable should be kept as short as possible.
Built-In Driver Overload Protection
As stated previously, the RS-485 spec requires that drivers
survive worst case bus contentions undamaged. The
ISL84XX devices meet this requirement via driver output
short circuit current limits, and on-chip thermal shutdown
circuitry.
The driver output stages incorporate short circuit current
limiting circuitry which ensures that the output current never
exceeds the RS-485 spec, even at the common mode
voltage range extremes. Additionally, these devices utilize a
foldback circuit which reduces the short circuit current, and
thus the power dissipation, whenever the contending voltage
exceeds either supply.
In the event of a major short circuit condition, ISL84XX
devices also include a thermal shutdown feature that
disables the drivers whenever the die temperature becomes
excessive. This eliminates the power dissipation, allowing
the die to cool. The drivers automatically reenable after the
die temperature drops about 15 degrees. If the contention
persists, the thermal shutdown/reenable cycle repeats until
the fault is cleared. Receivers stay operational during
thermal shutdown.
Low Power Shutdown Mode (ISL8483 Only)
These CMOS transceivers all use a fraction of the power
required by their bipolar counterparts, but the ISL8483
includes a shutdown feature that reduces the already low
quiescent I
whenever the receiver and driver are simultaneously
disabled (RE
600ns. Disabling both the driver and the receiver for less
than 50ns guarantees that the ISL8483 will not enter
shutdown.
Note that receiver and driver enable times increase when
the ISL8483 enables from shutdown. Refer to Notes 5-8, at
the end of the Electrical Specification table, for more
information.
1. Symbols are defined in the “MO Series Symbol List” in Section 2.2 of
Publication Number 95.
2. Dimensioning and tolerancing per ANSI Y14.5M-1982.
3. Dimension “D” does not include mold flash, protrusions or gate burrs.
Mold flash, protrusion and gate burrs shall not exceed 0.15mm (0.006
inch) per side.
4. Dimension “E” does not include interlead flash or protrusions. Interlead flash and protrusions shall not exceed 0.25mm (0.010 inch) per
side.
5. The chamfer on the body is optional. If it is not present, a visual index
feature must be located within the crosshatched area.
6. “L” is the length of terminal for soldering to a substrate.
7. “N” is the number of terminal positions.
8. Terminal numbers are shown for reference only.
9. The lead width “B”, as measured 0.36mm (0.014 inch) or greater
above the seating plane, shall not exceed a maximum value of
0.61mm (0.024 inch).
10. Controlling dimension: MILLIMETER. Converted inch dimensions
are not necessarily exact.
1. Symbols are defined in the “MO Series Symbol List” in Section 2.2 of
Publication Number 95.
2. Dimensioning and tolerancing per ANSI Y14.5M-1982.
3. Dimension “D” does not include mold flash, protrusions or gate burrs.
Mold flash, protrusion and gate burrs shall not exceed 0.15mm (0.006
inch) per side.
4. Dimension “E” does not include interlead flash or protrusions. Interlead
flash and protrusions shall not exceed 0.25mm (0.010 inch) per side.
5. The chamfer on the body is optional. If it is not present, a visual index
feature must be located within the crosshatched area.
6. “L” is the length of terminal for soldering to a substrate.
7. “N” is the number of terminal positions.
8. Terminal numbers are shown for reference only.
9. The lead width “B”, as measured 0.36mm (0.014 inch) or greater
above the seating plane, shall not exceed a maximum value of
0.61mm (0.024 inch).
10. Controlling dimension: MILLIMETER. Converted inch dimensions
are not necessarily exact.
All Intersil U.S. products are manufactured, assembled and tested utilizing ISO9000 quality systems.
Intersil Corporation’s quality certifications can be viewed at www.intersil.com/design/quality
Intersil products are sold by description only. Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without
notice. Accordingly, the reader is cautioned to verify that data she ets are current before placin g orders. Information furn ished by Intersil is believed to be accurate and
reliable. However, no responsibility is assumed by Intersil or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may result
from its use. No license is granted by implication or othe rwise under any patent or patent rights of Intersil or its subsidiaries.
For information regarding Intersil Corporation and its products, see www.intersil.com
16
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