SP385E-1 Datasheet, PDF (5/11 Pages) Sipex Corporation – True +3V or +5V RS-232 Line Driver/Receiver

FEATURES…
The Sipex SP385E-1 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 0.1µF capacitors, either
polarized or non–polarized, in +3V supplies.
The SP385E-1 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 SP385E-1
also includes a shutdown feature that tri-states
the drivers and the receivers.
The SP385E-1 includes a charge pump voltage
converter which allows it to operate from a single
+3.3V or +5V supply. These converters double the
V_CC voltage input in order to generate the EIA-232
or EIA-562 output levels. For +5V operation, the
SP385E-1 driver outputs adhere to all EIA-232-F
and CCITT V.28 specifications. While at +3.3V
operation, the outputs adhere to EIA-562 specifica-
tions. 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 SP385E-1 has a single control line which
simultaneously shuts down the internal DC/DC
converter and puts all transmitter and receiver
outputs into a high impedance state.
The SP385E-1 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 SP385E-1 is ideal for +3.3V battery
applications requiring low power operation.
The charge pump strength allows the drivers
to provide ±4.0V signals, plenty for typical
EIA-562 applications since the EIA-562
receivers have input sensitivity levels of less
than ±3V.
THEORY OF OPERATION
The SP385E-1 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 level transmitters, that
convert TTL or CMOS logic levels to ±5.0V
EIA/TIA-232 levels inverted relative to the
input logic levels. Typically the RS-232 output
voltage swing is ±5.5V with no load and at least
±5V minimum fully loaded. The driver outputs
are protected against infinite short-circuits to
ground without degradation in reliability. Driver
outputs will meet EIA/TIA-562 levels of ±3.7V
with supply voltages as low as 2.7V.
The instantaneous slew rate of the transmitter
output is internally limited to a maximum of
30V/µs in order to meet the standards [EIA 232-
D 2.1.7, Paragraph (5)]. However, the transition
region slew rate of these enhanced products is
typically 10V/µs. The smooth transition of the
loaded output from V_OL to V_OH 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
protected against voltages up to ±15V. Should
an input be left unconnected, a 5kΩ pull-down
resistor 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.
Rev. 07/26/02
SP385E-1 True +3V to +5V RS-232 Line Driver/Receiver
5
© Copyright 2001 Sipex Corporation