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  RS232 Transceivers for Hand Held Computers Withstand 10kV ESD &mdash DN64
  PDF, 81 Kb, Datei veröffentlicht: Nov 1, 1992
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  RS232 Transceivers for Hand Held Computers
  Withstand 10kV ESD -Design Note 64
  Sean Gold
  Battery-powered computers and instrumentation are
  often subjected to severe electrical stress which imposes
  some stringent demands on serial communication interfaces. As always, operating from a battery mandates
  minimal power consumption. Transceivers must also
  tolerate repetitive electrostatic discharge (ESD) pulses
  because cable connections frequently come in contact
  with humans and other charged bodies.
  ® Linear Technology’s LT 1237 addresses the above
  requirements. The LT1237 is a complete RS232 port,
  with three drivers, п¬Ѓve receivers and a regulated charge
  pump. Supply current is typically 6mA, but the device can
  be shut down with two separate logic controls. The driver
  disable pin shuts off the charge pump and the drivers –
  leaving all receivers active, ISUPPLY = 4mA. The ON/OFF
  pin shuts down all circuitry except for one micropower
  receiver, ISUPPLY = 60ОјA. The active receiver is useful
  for detecting start-up signals. The LT1237 operates up
  to 120kBaud and is fully compliant with all RS232 specifications. Connections to the RS232 cable are protected
  with internal ESD structures that can withstand repetitive
  В±10kV human body model ESD pulses. …

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  Regulator Circuit Generates Both 3.3V and 5V Outputs from 3.3V or 5V to Run Computers and RS232 &mdash DN71
  PDF, 89 Kb, Datei veröffentlicht: Jun 1, 1993
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  advertisement Regulator Circuit Generates Both 3.3V and 5V Outputs from
  3.3V or 5V to Run Computers and RS232 – Design Note 71
  David Dinsmore and Richard Markell
  Many portable microprocessor-based systems use a
  mix of 3.3V and 5V circuits. Some are still using only
  5V and inevitably some systems will end up being
  solely 3.3V based. If accessories are to be plugged
  into, or connected to any of these systems, a voltage
  conversion/power generation problem presents itself.
  The circuit shown in Figure 1 addresses the situation
  where either 5V or 3.3V power is available from the
  bus, but the accessory needs both 5V and 3.3V power. above the supply voltage and efficiently turns on and
  off the appropriate MOSFETs.
  IC2 also forms a flying capacitor buck/boost DC/DC
  converter circuit. This topology is used so that no
  transformers are necessary. Q1 is used to control this
  section’s voltage (V1). When VIN is at 5V, Q1 is off, forcing this section to operate as a step-down converter.
  It produces 3.3V which is sent to the 3.3V output of
  the circuit through IC4B. In this state, 5V power is sent
  directly through IC3A while IC3B and IC4A are off. The circuit consists of two sections, one being a DC/DC
  converter and the other being a pair of dual N-channel
  MOSFETs and their associated high side drivers that
  effectively form a DPDT switch. When VIN is at 3.3V, IC1 turns on Q1 shorting out the …

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  RS232 Interface Circuits for 3.3V Systems &mdash DN75
  PDF, 105 Kb, Datei veröffentlicht: Oct 1, 1993
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  RS232 Interface Circuits for 3.3V Systems – Design Note 75 Gary Maulding
  The rapid, widespread use of 3.3V logic circuits complicates the selection of RS232 interface circuits. The
  optimum choice of an interface circuit should be based
  upon several application dependent factors:
  1) Logic circuitry connected to interface chip port mouse. The LTВ®1342, LT1330, and LT1331 are all
  good RS232 transceiver choices for systems with both
  5V and 3V power. Typical performance waveforms for
  the LT1342 operating with VCC = 5V and VL = 3.3V are
  shown in Figure 2. 2) Power supply voltages available
  RECEIVER
  OUTPUT 3) Power consumption constraints
  4) Serial interface environment
  5) Mouse driving requirements
  As Figure 1 illustrates, 5V interface circuits cannot be
  used to directly connect to 3.3V CMOS logic circuits.
  The receiver output level will forward bias the logic
  circuit’s input protection diode, causing large current
  flow. In the worst case the CMOS logic circuit may
  latch up. Resistor voltage dividers or level shift buffers may be used to prevent forward biasing the CMOS
  input diode, but an RS232 transceiver designed for 3V
  logic application prevents this problem without extra
  components or power dissipation.
  Many of today’s systems have both 5V and 3V power …

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