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SP490E Datasheet(PDF) 7 Page - Sipex Corporation |
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SP490E Datasheet(HTML) 7 Page - Sipex Corporation |
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7 / 12 page  7 SP490EDS/14 SP490E Enhanced Full Duplex RS-485 Transceivers © Copyright 2000 Sipex Corporation FEATURES The SP490E and SP491E are full-duplex dif- ferential transceivers that meet the requirements of RS-485 and RS-422. Fabricated with a Sipex proprietary BiCMOS process, both products require a fraction of the power of older bipolar designs. THEORY OF OPERATION The RS-485 standard is ideal for multi-drop applications or for long-distance interfaces. RS-485 allows up to 32 drivers and 32 receivers to be connected to a data bus, making it an ideal choice for multi-drop applications. Since the cabling can be as long as 4,000 feet, RS-485 transceivers are equipped with a wide (-7V to +12V) common mode range to accommodate ground potential differences. Because RS-485 is a differential interface, data is virtually immune to noise in the transmission line. Drivers The drivers for both the SP490E and SP491E have differential outputs. The typical voltage output swing with no load will be 0 volts to +5 volts. With worst case loading of 54 Ω across the differential outputs, the driver can maintain greater than 1.5V voltage levels. The driver of the SP491E has a driver enable control line which is active high. A logic high on DE (pin 4) of the SP491E will enable the differ- ential driver outputs. A logic low on DE (pin 4) of the SP491E will tri-state the driver outputs. The SP490E does not have a driver enable. Receivers The receivers for both the SP490E and SP491E have differential inputs with an input sensitivity as low as ±200mV. Input impedance of the receivers is typically 15k Ω (12kΩ minimum). A wide common mode range of -7V to +12V allows for large ground potential differences between systems. The receivers for both the SP490E and SP491E are equipped with the fail-safe feature. Fail-safe guarantees that the receiver output will be in a high state when the input is left unconnected. The receiver of the SP491E has a receiver enable control line which is active low. A logic low on REB (pin 3) of the SP491E will enable the differential receiver. A logic high on REB (pin 3) of the SP491E will tri-state the receiver. ESD Tolerance The SP490E/SP491E devices incorporate ruggedized ESD cells on all driver output and receiver input pins. The ESD structure is improved over our previous family for more rugged applications and environments sensitive to electro-static discharges and associated transients. The improved ESD tolerance is at least ±15kV without damage nor latch-up. R RC C C CSS R RSS SW1 SW1 SW2 SW2 RC Device Under Test DC Power Source CS RS SW1 SW2 Figure 9. ESD Test Circuit for Human Body Model |
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