XR3170E Datasheet, PDF (16/24 Pages) Exar Corporation – 3.3V High Speed RS-485/RS-422 TRANSCEIVERS WITH 1/8 UNIT LOAD

XR3170E-3178E
3.3V HIGH SPEED RS-485/RS-422 TRANSCEIVERS WITH 1/8^th UNIT LOAD
REV. 1.0.0
1.0 PRODUCT DESCRIPTION
XR3170E-XR3178E is a family of advanced RS-485/RS-422 transceivers. Each contains one driver and one
receiver. All devices operate from a single +3.3V supply. The XR3172E, XR3175E and XR3178E are a half-
duplex design while the other devices are full-duplex designs. The control pins RE and DE feature a hotswap
capability allowing live insertion without spurious data transfer. Drivers are output short-circuit current limited.
Thermal-shutdown circuitry protects drivers against excessive power dissipation. When activited, the thermal-
shutdown circuitry forces the driver outptus into a high-impedance state.
ADVANCED FAILSAFE
Ordinary RS-485 differential receivers will be in an indeterminate state whenever the data bus is not being
actively driven. The Advanced Failsafe feature of the XR3170E family guarantees a logic-high receiver output
when the receiver inputs are open or shorted, or when they are connected to a terminated transmission line
with all drivers disabled. In a terminated bus with all transmitters disabled, the receivers’ differential input
voltage is pulled to 0V by the termination. The XR3170E family interprets 0V differential as a logic high with a
minimum 50mV noise margin while maintaining compliance with the EIA/TIA-485 standard of +/-200mV.
RECEIVER INPUT FILTERING
XR3170E-XR3175E receivers incorpoprate input filtering in addition to input hysteresis. This filtering enhances
noise immunity with differential signals that have very slow rise and fall times. Receiver propagation delay
increases slightly due to this filtering. XR3176E, XR3177E abd XR3178E high speed devices do not have this
input filtering.
HOT-SWAP CAPABILITY
When Vcc is first applied the XR3170E family holds the driver enable and receiver enable inactive for
approximately 10 microseconds. During power ramp-up other system IC’s may drive unpredictable values.
Hot-swap capability prevents the XR3170E family from driving any output signal until power has stabilized.
After the initial power-up sequence, the hot-swap circuit becomes transparent and driver enable and receiver
enable resume their normal functions and timings.
If circuit boards are inserted into an energized backplane (commonly called "live insertion" or "hot-swap")
power may suddenly be applied to all circuits. Without the hot-swap capability, this situation could improperly
enable the transceiver’s driver or receiver, driving invalid data onto shared busses and possibly causing driver
contention or device damage.
+/-15kV ESD PROTECTION
ESD protection structures are incorporated on all pins to protect against electrostatic discharges encountered
during handling and assembly. The driver outputs and receiver inputs of the XR3170E family have extra
protection against static electricity. Exar uses state of the art structures to protect these pins against ESD of
+/-15kV without damage. The ESD structures withstand high ESD in all states: normal operation, shutdown
and powered down. After an ESD event, the XR3170E-XR3178E keep operating without latch-up or damage.
ESD protection can be tested in various ways. The transmitter outputs and receiver inputs of the XR3170E-
XR3178E are characterized for protection to the following limits:
■ +/-15kV using the Human Body Model
■ +/-8kV using the Contact Discharge Model
■ +/-15kV Air-gap Discharge Model
ESD TEST CONDITIONS
ESD performance depends on a variety of conditions. Contact Exar for a reliability report that documents test
setup, methodology and results.
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