DESCRIPTION
The
SP3222E/3232E
transceivers meet the EIA/
TIA-232 and V.28/V.24 communication proto-
cols and can be implemented in battery-pow-
ered, portable, or hand-held applications such as
notebook or palmtop computers. The
SP3222E/
3232E
devices all feature
Sipex's
proprietary
on-board charge pump circuitry that generates 2
x V
CC
for RS-232 voltage levels from a single
+3.0V to +5.5V power supply. This series is
ideal for +3.3V-only systems, mixed +3.3V to
+5.5V systems, or +5.0V-only systems that re-
quire true RS-232 performance. The
SP3222E/
3232E
series have drivers that operate at a typi-
cal data rate of 235Kbps fully loaded.
The
SP3222E
and
SP3232E
are 2-driver/2-re-
ceiver devices ideal for portable or hand-held
applications. The
SP3222E
features a 1µA
shutdown mode that reduces power consump-
tion and extends battery life in portable systems.
Its receivers remain active in shutdown mode,
allowing external devices such as modems to be
monitored using only 1µA supply current.
THEORY OF OPERATION
The
SP3222E/3232E
series are made up of three
basic circuit blocks: 1. Drivers, 2. Receivers,
and 3. the Sipex proprietary charge pump.
Drivers
The drivers are inverting level transmitters that
convert TTL or CMOS logic levels to
±5.0V
EIA/TIA-232 levels inverted relative to the in-
put 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 drivers typically can operate at a data rate
of 235Kbps. The drivers can guarantee a data
rate of 120Kbps fully loaded with 3KΩ in
parallel with 1000pF, ensuring compatibility
with PC-to-PC communication software.
Date: 02/24/05
The slew rate of the driver output is internally
limited to a maximum of 30V/µs in order to meet
the EIA standards (EIA RS-232D 2.1.7, Para-
graph 5). The transition of the loaded output
from HIGH to LOW also meets the monotonic-
ity requirements of the standard.
The
SP3222E/3232E
drivers can maintain high
data rates up to 235Kbps fully loaded.
Figure 8
shows a loopback test circuit used to test the
RS-232 drivers.
Figure 9
shows the test results
of the loopback circuit with all drivers active at
120Kbps with RS-232 loads in parallel with
1000pF capacitors.
Figure 10
shows the test
results where one driver was active at 235Kbps
and all drivers loaded with an RS-232 receiver
in parallel with a 1000pF capacitor. A solid
RS-232 data transmission rate of 120Kbps
provides compatibility with many designs
in personal computer peripherals and LAN
applications.
The
SP3222E
driver's output stages are turned
off (tri-state) when the device is in shutdown
mode. When the power is off, the
SP3222E
device permits the outputs to be driven up to
±12V.
The driver's inputs do not have pull-up
resistors. Designers should connect unused
inputs to V
CC
or GND.
In the shutdown mode, the supply current falls to
less than 1µA, where SHDN = LOW. When the
SP3222E
device is shut down, the device's
driver outputs are disabled (tri-stated) and the
charge pumps are turned off with V+ pulled
down to V
CC
and V- pulled to GND. The time
required to exit shutdown is typically 100µs.
Connect SHDN to V
CC
if the shutdown mode is
not used. SHDN has no effect on RxOUT or
RxOUTB. As they become active, the two driver
outputs go to opposite RS-232 levels where one
driver input is HIGH and the other LOW. Note
that the drivers are enabled only when the
magnitude of V- exceeds approximately 3V.
SP3222E, SP3232E True +3.0 to +5.0V RS-232 Transceivers
© Copyright 2005 Sipex Corporation
8
SIPEX [ SIPEX CORPORATION ]
