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SP385A Datasheet(PDF) 5 Page - Sipex Corporation |
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SP385A Datasheet(HTML) 5 Page - Sipex Corporation |
5 / 9 page 5 SP385ADS/05 SP385A Line Driver/Receiver © Copyright 2000 Sipex Corporation FEATURES… The Sipex SP385A is a +3V to +5V EIA-232/EIA- 562 line transceiver. It is a pin-for-pin alternative for the SP310A and will operate in the same socket with capacitors ranging from 0.1 µF to 10µF, either polar- izedornon–polarized,in+3Vsupplies. TheSP385A offers the same features such as 120kbps guaranteed transmission rate, increased drive current for longer and more flexible cable configurations, low power dissipation and overall ruggedized construction for commercial and industrial environments. The SP385A also includes a shutdown feature that tri-states the drivers and the receivers. The SP385A includes a charge pump voltage con- verter which allows it to operate from a single +3.3V or +5V supply. These converters double the V CC voltageinputinordertogeneratetheEIA-232orEIA- 562 output levels. For +5V operation, the SP385A driver outputs adhere to all EIA-232D and CCITT V.28 specifications. While at +3.3V operation, the outputs adhere to EIA-562 specifications. Due to Sipex's efficient charge pump design, the charge pump levels and the driver outputs are less noisy than other 3V EIA-232 transceivers. The SP385A has a single control line which simul- taneously shuts down the internal DC/DC con- verter and puts all transmitter and receiver outputs into a high impedance state. The SP385A is available in 18-pin plastic SOIC and 20-pin plastic SSOP packages for operation over commercial and industrial temperature ranges. Please consult the factory for surface- mount packaged parts supplied on tape-on-reel as well as parts screened to MIL-M-38510. The SP385A is ideal for +3.3V battery applica- tions requiring low power operation. The charge pump strength allows the drivers to provide ±4.0V signals, plenty for typical EIA-232 applications since the EIA-232 receivers have input sensitivity levels of less than ±3V. THEORY OF OPERATION The SP385A device is made up of three basic circuit blocks — 1) a driver/transmitter, 2) a receiver and 3) a charge pump. Driver/Transmitter The drivers are inverting transmitters, which accept TTL or CMOS inputs and output the RS-232 signals with an inverted sense relative to the input logic levels. Typically the RS-232 output voltage swing is ±9V for 5V supply and ±4.2V for 3.3V supply. Even under worst case loading conditions of 3k Ω and 2500pF, the output is guar- anteed to be ±5V for a 5V supply and ±3.7V for a 3.3V supply which adheres to EIA-232 and EIA- 562 specifications, respecitively. The transmitter outputs are protected against infinite short-circuits to ground without degradation in reliability. The instantaneous slew rate of the transmitter output is internally limited to a maximum of 30V/ µsinordertomeetthestandards[EIA232-D2.1.7, Paragraph (5)]. However, the transition region slew rate of these enhanced products is typically 10V/ µs.Thesmoothtransitionoftheloadedoutput from V OL to VOH clearly meets the monotonicity requirements of the standard [EIA 232-D 2.1.7, Paragraphs (1) & (2)]. Receivers The receivers convert RS-232 input signals to inverted TTL signals. Since the input is usually from a transmission line, where long cable lengths and system interference can degrade the signal, the inputs have a typical hysteresis margin of 500mV. This ensures that the receiver is virtually immune to noisy transmission lines. The input thresholds are 0.8V minimum and 2.4V maximum, again well within the ±3V RS-232 requirements. The receiver inputs are also pro- tected against voltages up to ±15V. Should an input be left unconnected, a 5k Ω pull-down resis- tor to ground will commit the output of the receiver to a high state. In actual system applications, it is quite possible for signals to be applied to the receiver inputs before power is applied to the receiver circuitry. This occurs for example when a PC user attempts to print only to realize the printer wasn’t turned on. In this case an RS-232 signal from the PC will appear on the receiver input at the printer. When the printer power is turned on, the receiver will operate normally. All of these enhanced devices are fully protected. |
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