SP3222E Datasheet, PDF (8/20 Pages) Sipex Corporation – True +3.0V to +5.5V RS-232 Transceivers

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.
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 if the shutdown mode is
CC
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.
Date: 02/24/05
SP3222E, SP3232E True +3.0 to +5.0V RS-232 Transceivers
8
© Copyright 2005 Sipex Corporation