FEATURES…
The
Sipex SP385E
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 0.1µF to 10µF, either polar-
ized or non–polarized, in +3V supplies. The
SP385E
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
commercialandindustrialenvironments. The
SP385E
also includes a shutdown feature that tri-states the
drivers and the receivers.
The
SP385E
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
voltage input in order to generate the EIA-232 or EIA-
562 output levels. For +5V operation, the
SP385E
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
SP385E
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
SP385E
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
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 appli-
cations since the EIA-232 receivers have input
sensitivity levels of less than
±3V.
THEORY OF OPERATION
The
SP385E
device is made up of three basic
circuit blocks — 1) a driver/transmitter, 2) a re-
ceiver and 3) a charge pump.
Driver/Transmitter
The drivers are inverting transmitters, which ac-
cept 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 3kΩ and 2500pF, the output is guaranteed to be
±5V
for a 5V supply and
±3.7V
for a 3.3V supply
which adheres to EIA-232 and EIA-562 specifica-
tions, respectively. 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/
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 out-
put from V
OL
to V
OH
clearly meets the monotonic-
ity 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 5kΩ 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.
Rev. 10/22/01
SP385E Enhanced +3V to +5V RS-232 Line Driver/Receiver
© Copyright 2001 Sipex Corporation
5
SIPEX [ SIPEX CORPORATION ]
