ISL32496EIUZ Datasheet, PDF (12/22 Pages) Intersil Corporation – ±60V Fault Protected, 5V, RS-485/RS-422 Transceivers with ±25V CMR and ESD Protection

ISL32490E, ISL32492E, ISL32493E, ISL32495E, ISL32496E, ISL32498E
increases system reliability. The CMR increases to ±25V, while
the RS-485 bus pins (receiver inputs and driver outputs) include
fault protection against voltages and transients up to ±60V.
Additionally, larger-than-required differential output voltages
(V_OD) increase noise immunity, while the ±16.5kV built-in ESD
protection complements the fault protection.
Receiver (Rx) Features
These devices utilize a differential input receiver for maximum
noise immunity and common mode rejection. Input sensitivity is
better than ±200mV, as required by the RS-422 and RS-485
specifications.
Receiver input (load) current surpasses the RS-422 specification
of 3mA and is four times lower than the RS-485 “Unit Load (UL)”
requirement of 1mA maximum. Thus, these products are known
as “one-quarter UL” transceivers, and there can be up to 128 of
these devices on a network while still complying with the RS-485
loading specification.
The Rx functions with common mode voltages as great as ±25V,
making them ideal for industrial or long networks where induced
voltages are a realistic concern.
All the receivers include a “full fail-safe” function 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 (i.e., an idle bus).
Rx outputs feature high drive levels (typically 22mA @ V_OL = 1V) to
ease the design of optically coupled isolated interfaces.
Receivers easily meet the data rates supported by the
corresponding driver, and all receiver outputs are three-statable
via the active low RE input.
The Rx in the 250kbps and 1Mbps versions include noise filtering
circuitry to reject high-frequency signals. The 1Mbps version
typically rejects pulses narrower than 50ns (equivalent to
20Mbps), while the 250kbps Rx rejects pulses below 150ns
(6.7Mbps).
Driver (Tx) Features
The RS-485/RS-422 driver is a differential output device that
delivers at least 1.5V across a 54Ω load (RS-485) and at least
2.4V across a 100Ω load (RS-422). The drivers feature low
propagation delay skew to maximize bit width and minimize EMI,
and all drivers are three-statable via the active high DE input.
The 250kbps and 1Mbps driver outputs are slew rate limited to
minimize EMI and to minimize reflections in unterminated or
improperly terminated networks. Outputs of the ISL32496E and
ISL32498E drivers are not limited; thus, faster output transition
times allow data rates of at least 15Mbps.
High Overvoltage (Fault) Protection
Increases Ruggedness
NOTE: The available smaller pitch package (MSOP) may not meet the
creepage and clearance (C&C) requirements for ±60V levels. The user is
advised to determine his C&C requirements before selecting a package
type.
The ±60V (referenced to the IC GND) fault protection on the
RS-485 pins makes these transceivers some of the most rugged
on the market. This level of protection makes the ISL3249xE
perfect for applications where power (e.g., 24V and 48V supplies)
must be routed in the conduit with the data lines, or for outdoor
applications where large transients are likely to occur. When
power is routed with the data lines, even a momentary short
between the supply and data lines will destroy an unprotected
device. The ±60V fault levels of this family are at least five times
higher than the levels specified for standard RS-485 ICs. The
ISL3249xE protection is active whether the Tx is enabled or
disabled, and even if the IC is powered down.
If transients or voltages (including overshoots and ringing)
greater than ±60V are possible, then additional external
protection is required.
Widest Common Mode Voltage (CMV)
Tolerance Improves Operating Range
RS-485 networks operating in industrial complexes or over long
distances are susceptible to large CMV variations. Either of these
operating environments may suffer from large node-to-node
ground potential differences or CMV pickup from external
electromagnetic sources, and devices with only the minimum
required +12V to -7V CMR may malfunction. The ISL3249xE’s
extended ±25V CMR is the widest available, allowing operation in
environments that would overwhelm lesser transceivers.
Additionally, the Rx will not phase invert (erroneously change
state), even with CMVs of ±40V or differential voltages as large
as 40V.
High V_OD Improves Noise Immunity and
Flexibility
The ISL3249xE driver design delivers larger differential output
voltages (V_OD) than the RS-485 standard requires or than most
RS-485 transmitters can deliver. The typical ±2.5V V_OD provides
more noise immunity than networks built using many other
transceivers.
Another advantage of the large V_OD is the ability to drive more
than two bus terminations, which allows for utilizing the
ISL3249xE in “star” and other multi-terminated, nonstandard
network topologies. Figure 10 on page 14 details the
transmitter’s V_OD vs I_OUT characteristic and includes load lines
for four (30Ω) and six (20Ω) 120Ω terminations. Figure 10 shows
that the driver typically delivers ±1.3V into six terminations, and
the “Electrical Specifications” on page 5 guarantees a V_OD of
±0.8V at 21Ω over the full temperature range. The RS-485
standard requires a minimum 1.5V V_OD into two terminations,
but the ISL3249xE deliver RS-485 voltage levels with 2x to 3x the
number of terminations.
Hot Plug Function
When a piece of equipment powers up, there is a period of time
during which the processor or ASIC driving the RS-485 control
lines (DE, RE) is unable to ensure that the RS-485 Tx and Rx
outputs are kept disabled. If the equipment is connected to the
bus, a driver activating prematurely during power-up may crash
the bus. To avoid this scenario, the ISL3249xE devices
incorporate a “Hot Plug” function. Circuitry monitoring V_CC ensures
that, during power-up and power-down, the Tx and Rx outputs
remain disabled, regardless of the state of DE and RE, if V_CC is less
12
FN7786.2
March 16, 2012