XR3070-78X Datasheet, PDF (18/24 Pages) Exar Corporation – LOW POWER 18V TOLERANT RS-485/RS-422 +3.3V TRANSCEIVERS

XR3070-78X
LOW POWER 18V TOLERANT RS-485/RS-422 +3.3V TRANSCEIVERS
REV. 1.0.2
±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 XR3070-78X 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 XR3070-78X keep operating without latch-up or damage.
ESD protection can be tested in various ways. The transmitter outputs and receiver inputs of the XR3070-78X
are characterized for protection to the following limits:
±15kV using the Human Body Model
± 8kV 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.
IEC 61000-4-2
The IEC 61000-4-2 standard covers ESD testing and performance of finished equipment. However, it does not
specifically refer to integrated circuits. The XR3070-78X family helps you design equipment to meet
IEC 61000-4-2, without sacrificing board-space and cost for external ESD-protection components.
The major differences between tests done using the Human body model and IEC 61000-4-2 is a higher peak
current in IEC 61000-4-2. Series resistance is lower in the IEC 61000-4-2 model. Hence, the ESD withstand
voltage measured to IEC 61000-4-2 is generally lower than that of human body model.
The air-gap test involves approaching the device with a charged probe. The contact discharge method
connects the probe to the device before the probe is energized.
256 TRANSCEIVERS ON THE BUS
The standard RS-485 receiver input impedance is 12k Ohms (1 unit load). A standard driver can drive up to 32
unit loads. The XR3070-78X family of transceivers have a 1/8^th unit load receiver input impedance of 96kW,
allowing up to 256 transceivers to be connected in parallel on a communication line. Any combination of these
devices and other RS-485 transceivers up to a total of 32 unit loads may be connected to the line.
LOW POWER SHUTDOWN MODE
Low-power shutdown mode is initiated by bringing both RE high and DE low simultaneously. While in shutdown
devices draw less than 1μA of supply current. DE and RE may be tied together and driven by a single control
signal. Devices are guaranteed not to enter shutdown if RE is high and DE is low for less than 50ns. If the
inputs are in this state for at least 600ns, the parts will enter shutdown.
Enable times t_ZH and t_ZL apply when the part is not in low-power shutdown state. Enable times t_ZH(SHDN) and
t_ZL(SHDN) apply when the parts are shutdown. The drivers and receivers take longer to become enabled from
low-power shutdown t_ZH(SHDN) and t_ZL(SHDN) than from driver / receiver disable mode (t_ZH and t_ZL).
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