ISL3158AEMBZ Intersil, ISL3158AEMBZ Datasheet - Page 11

• Manufacturer Part Number: ISL3158AEMBZ
• Description: TXRX ESD 5V RS485/422 8-SOIC
• Manufacturer: Intersil
• Type: Transceiverr

Specifications of ISL3158AEMBZ

• Number Of Drivers/receivers: 1/1
• Protocol: RS422, RS485
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ESD Protection
All pins on this device includes 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 ISL3158AE 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 ISL3158AE
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 10Mbps
are limited to lengths of less than 100’.
11
ISL3158AE
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 10Mbps
devices, to minimize reflections. 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 limit 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.
Low Power Shutdown Mode
This CMOS transceiver uses a fraction of the power required
by it’s bipolar counterparts, but it also includes a shutdown
feature that reduces the already low quiescent I
trickle. This device enters shutdown whenever the receiver
and driver are simultaneously disabled (RE = V
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 5, 6,
7, 8 and 9, at the end of the “Electrical Specification” table on
page 6, for more information.
CC
CC
to a 70nA
April 3, 2009
and
FN6886.0