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ISL3150EIUZ Datasheet(PDF) 13 Page - Intersil Corporation

Part No. ISL3150EIUZ
Description  ±16.5kV ESD, Large Output Swing, 5V, Full Fail-Safe, 1/8 Unit Load, RS-485/RS-422 Transceivers
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Maker  INTERSIL [Intersil Corporation]
Homepage  http://www.intersil.com/cda/home
Logo INTERSIL - Intersil Corporation

ISL3150EIUZ Datasheet(HTML) 13 Page - Intersil Corporation

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13
FN6363.2
July 30, 2009
ESD Protection
All pins on these devices include class 3 (>7kV)
Human Body Model (HBM) ESD protection structures,
but the RS-485 pins (driver outputs and receiver
inputs) incorporate advanced structures allowing
them to survive ESD events in excess of ±16.5kV
HBM and ±16.5kV (1/2 duplex) IEC61000-4-2. The
RS-485 pins are particularly vulnerable to ESD strikes
because they typically connect to an exposed port on
the exterior of the finished product. Simply touching
the port pins, or connecting a cable, can cause an
ESD event that might destroy unprotected ICs. These
new ESD structures protect the device whether or not
it is powered up, and without degrading the RS-485
common mode range of -7V to +12V. This built-in
ESD protection eliminates the need for board level
protection structures (e.g., transient suppression
diodes), and the associated, undesirable capacitive
load they present.
IEC61000-4-2 Testing
The IEC61000 test method applies to finished
equipment, rather than to an individual IC. Therefore,
the pins most likely to suffer an ESD event are those that
are exposed to the outside world (the RS-485 pins in this
case), and the IC is tested in its typical application
configuration (power applied) rather than testing each
pin-to-pin combination. The IEC61000 standard’s lower
current limiting resistor coupled with the larger charge
storage capacitor yields a test that is much more severe
than the HBM test. The extra ESD protection built into
this device’s RS-485 pins allows the design of equipment
meeting level 4 criteria without the need for additional
board level protection on the RS-485 port.
AIR-GAP DISCHARGE TEST METHOD
For this test method, a charged probe tip moves toward
the IC pin until the voltage arcs to it. The current
waveform delivered to the IC pin depends on approach
speed, humidity, temperature, etc., so it is difficult to
obtain repeatable results. The ISL315xE 1/2 duplex
RS-485 pins withstand ±16.5kV air-gap discharges.
CONTACT DISCHARGE TEST METHOD
During the contact discharge test, the probe contacts the
tested pin before the probe tip is energized, thereby
eliminating the variables associated with the air-gap
discharge. The result is a more repeatable and
predictable test, but equipment limits prevent testing
devices at voltages higher than ±9kV. The RS-485 pins of
all the ISL315xE versions survive ±9kV contact
discharges.
Data Rate, Cables, and Terminations
RS-485/RS-422 are intended for network lengths up to
4000’, but the maximum system data rate decreases as
the transmission length increases. Devices operating at
20Mbps are limited to lengths less than 100’, while the
115kbps versions can operate at full data rates with
lengths of several 1000’.
Twisted pair is the cable of choice for RS-485/RS-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 20Mbps
devices, to minimize reflections. Short networks using
the 115kbps 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 specification requires
that drivers survive worst case bus contentions
undamaged. These 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 specification, even at the
common mode voltage range extremes.
In the event of a major short circuit condition, 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 re-enable after
the die temperature drops about 15°C. If the contention
persists, the thermal shutdown/re-enable cycle repeats
until the fault is cleared. Receivers stay operational
during thermal shutdown.
Low Power Shutdown Mode
These CMOS transceivers all use a fraction of the power
required by their bipolar counterparts, but they also
include a shutdown feature that reduces the already low
quiescent ICC to a 70nA trickle. These devices enter
shutdown whenever the receiver and driver are
simultaneously disabled (RE =VCC and DE = GND)
for a period of at least 600ns. Disabling both the driver
and the receiver for less than 60ns guarantees that the
transceiver will not enter shutdown.
Note that receiver and driver enable times increase when
the transceiver enables from shutdown. Refer to Notes 9,
10, 11, 12 and 13, at the end of the “Electrical
Specification” table on page 9, for more information.
ISL3150E, ISL3152E, ISL3153E, ISL3155E, ISL3156E, ISL3158E


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