ISL3159EIRZ Intersil, ISL3159EIRZ Datasheet - Page 9

• Manufacturer Part Number: ISL3159EIRZ
• Description: TXRX ESD 5V RS-485/422 10-DFN
• Manufacturer: Intersil
• Type: Transceiverr

Specifications of ISL3159EIRZ

• Number Of Drivers/receivers: 1/1
• Protocol: RS422, RS485
• Voltage - Supply: 4.5 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 10-DFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

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
point-to-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 mix 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’ (~1200m), so the wide CMR is necessary to
handle ground potential differences, as well as voltages
induced in the cable by external fields.
Receiver (Rx) Features
This transceiver utilizes a differential input receiver for
maximum noise immunity and common mode rejection. Input
sensitivity is ±200mV, as required by the RS422 and RS-485
specifications. 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, or
industrial environments, where induced voltages are a
realistic concern.
The receiver input resistance of 50kΩ surpasses the RS-422
spec of 4kΩ, and is five times the RS-485 “Unit Load” (UL)
requirement of 12kΩ minimum. Thus, the ISL3159E is
known as a “one-fifth UL” transceiver, and there can be up to
160 devices on the RS-485 bus while still complying with the
RS-485 loading specification.
The receiver is a “full fail-safe” version that guarantees a
high level receiver output if the receiver inputs are
unconnected (floating), shorted together, or connected to a
terminated bus with all the transmitters disabled
(terminated/undriven).
Rx outputs deliver large low state currents (typically >30mA)
at V
networks).
Receivers easily meet the 40Mbps data rate supported by
the driver, and the receiver output is tri-statable via the active
low RE input.
Driver (Tx) Features
The RS-485/RS-422 driver is a differential output device that
delivers at least 2.1V across a 54Ω load (RS-485/
PROFIBUS), and at least 2.6V across a 100Ω load (RS-422)
even with V
delay skew to maximize bit width, and to minimize EMI.
OL
= 1V (to ease the design of optically coupled isolated
CC
= 4.5V. The drivers feature low propagation
9
ISL3159E
Outputs of the drivers are not slew rate limited, so faster
output transition times allow data rates of at least 40Mbps.
Driver outputs are tri-statable via the active high DE input.
For parallel applications, bit-to-bit skews between any two
ISL3159E transmitter and receiver pairs are guaranteed to
be no worse than 8ns (4ns max for any two Tx, 4ns max for
any two Rx).
High V
The ISL3159E driver design delivers larger differential output
voltages (V
most RS-485 transmitters can deliver. The minimum ±2.1V
V
networks built using standard 1.5V V
Another advantage of the large V
more than two bus terminations, which allows for utilizing the
ISL3159E in “star” and other multi-terminated,
“non-standard” network topologies. Figure 8, details the
transmitter’s V
lines for four (30Ω) and six (20Ω) 120Ω terminations. The
figure shows that the driver typically delivers 1.9/1.5V into
4/6 terminations, even at +85
requires a minimum 1.5V V
ISL3159E typically delivers RS-485 voltage levels with 2x to
3x the number of terminations.
ESD Protection
All pins on the ISL3159E include class 3 (>9kV) 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 ±15kV
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
OD
guarantees at least ±600mV more noise immunity than
OD
Improves Noise Immunity and Flexibility
OD
) than the RS-485 standard requires, or than
OD
vs I
OUT
characteristic, and includes load
OD
°
C. The RS-485 standard
into two terminations, but the
OD
OD
is the ability to drive
transmitters.
July 26, 2007
FN6364.0