SP3222 Datasheet, PDF (8/20 Pages) Sipex Corporation – True +3.0V to +5.5V RS-232 Transceivers

DESCRIPTION
The SP3222/3232E 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 SP3222/
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 SP3222/
3232E series have drivers that operate at a typi-
cal data rate of 235Kbps fully loaded.
The SP3222 and SP3232 are 2-driver/2-receiver
devices ideal for portable or hand-held applica-
tions. The SP3222 features a 1µA shutdown
mode that reduces power consumption and ex-
tends battery life in portable systems. Its receiv-
ers remain active in shutdown mode, allowing
external devices such as modems to be moni-
tored using only 1µA supply current.
THEORY OF OPERATION
The SP3222/3232E 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 SP3222/3232E 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 SP3222 driver's output stages are turned off
(tri-state) when the device is in shutdown mode.
When the power is off, the SP3222 device per-
mits 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
SP3222 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.
Rev. 07/01/03
SP3222/3232E True +3.0 to +5.0V RS-232 Transceivers
8
© Copyright 2003 Sipex Corporation