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LT1081

Design Notes

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  Extending the Applications of 5V Powered RS232 Transceivers &mdash DN14
  PDF, 102 Kb, File published: Sep 1, 1988
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  Extending the Applications of 5V Powered RS232 Transceivers
  Design Note 14 High Speed Operation
  Although the EIA RS232 specification is for a relatively
  slow communications protocol, many applications
  require RS232 transceivers to operate at higher frequencies. Devices such as the LTВ®1080, LT1081, and the
  LT1130 series share a common design for the drivers
  and receivers and are capable of operating over 100
  kilobaud.
  Although the slew rate is controlled for all of the Linear
  Technology series of RS232 communications devices,
  for output levels limited to В±6V the transition time is
  fast enough to allow high baud rates. With a slew rate
  of approximately 10V per microsecond, it only takes
  1.2 microseconds for a 12V excursion. The two photos
  (Figure 1 and Figure 2) show the output waveform and
  delay associated with a 75kHz square wave input and a
  100kHz square wave. Delay times are in the order of 0.5
  microseconds and the total slew time is approximately 1.2 microseconds. Output load is 3k. Receivers are
  much faster and can handle these baud rates with no
  problem. For higher communication rates, a differential
  signal is recommended.
  Power Supply Tricks
  The power supply generator on 5V powered devices is …

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  Design Considerations for RS-232 Interfaces &mdash DN27
  PDF, 319 Kb, File published: Oct 1, 1989
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  Design Considerations for RS232 Interfaces
  Design Note 27
  Sean Gold Table 1. Key RS232 Transceiver Specifications
  (EIA RS232C.V28)
  SPECIFICATIONS
  Signal Levels
  Cable Length
  Load Capacitance
  Cable Termination
  Data Rate
  Slew Rate
  Fault Conditions VALUE
  В±15 Max; В±5 Min
  50 Max
  2500 Max
  3k < R < 7k
  20k Max
  3 < SR < 30
  Drivers Must Tolerate: Conductor to Conductor Shorts Line Open Circuit В±25V Line Overage UNITS
  V
  Ft
  pF
  О© …

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  RS232 Transceiver with Automatic Power Shutdown Control &mdash DN30
  PDF, 122 Kb, File published: Jan 1, 1990
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  RS232 Transceiver with Automatic Power Shutdown Control
  Design Note 30
  Sean Gold
  The LTВ®1180/81 RS232 transceivers with on-chip
  charge pumps offer some unique features that greatly
  enhance serial interface performance. Like the LT1080
  and LT1130 series transceivers, the LT1180 is fully
  compliant with all RS232 specifications. The LT1180 is
  unique since it utilizes a charge pump which oscillates
  at 150kHz to 200kHz – about twice the frequency of the
  standard transceivers. In addition to providing excellent
  current delivery capability, the high speed charge pump
  can operate with storage capacitors as small as 0.1ОјF.
  Reducing storage capacitor size to 0.1ОјF shrinks board
  space, thereby lowering production costs. Small capacitors also shorten the transceiver turn-on time to
  less than 200Ојs, which makes the LT1180 ideal for applications which must address the RS232 transceiver quickly. The interface described here takes advantage
  of fast turn-on to reduce power dissipation.
  The circuit shown in Figure 1 automatically shuts down
  when there is no data flow through the interface. A data
  stream on either the RS232 or logic inputs activates
  the transceiver. The data must begin with a logic 1
  preamble, and the data stream must contain a sufficient number of 1’s to keep the transceiver active. The
  preamble may be as short as 50Ојs. Alternatively, the …

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  New Developments in RS232 Interfaces &mdash DN4
  PDF, 73 Kb, File published: Nov 1, 1987
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  New Developments in RS232 Interfaces
  Design Note 4
  Robert Dobkin
  New RS232 interface chips have been developed that
  offer significant advantages over older devices such
  as the 1488 and 1489. The new RS232 interface ICs
  improve speed, power, voltage supply requirements, and
  protection over older devices. Further, the new chips
  are easier to use, requiring fewer external components
  and may be turned off to a “zero” power supply current
  condition for use in battery powered systems.
  The new RS232 drivers are implemented in a monolithic
  bipolar technology. A unique output stage was designed
  that provides large output swings, minimizing power
  supply voltage requirements, while retaining outstanding overload protection features. The outputs can be
  driven beyond the power supply voltage without drawing excessive current or forcing current back into the
  power supplies. Of course, current limiting is included
  to protect against short circuit conditions.
  Initial consideration of technologies for implementing
  RS232 interfacing might include CMOS as a possible
  technology for this type of application. Power supply
  requirements are low, output voltage swing is high,
  and higher voltage CMOS technologies are available …

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Manufacturer's Classification

• Interface > RS232/RS562 Transceivers