SP3222B Datasheet, PDF (8/18 Pages) Sipex Corporation – True +3.0V to +5.5V RS-232 Transceivers

DESCRIPTION
The SP3222B/3232B 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
SP3222B/3232B devices all feature Sipex's pro-
prietary 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 require true RS-232 performance.
The SP3222B/3232B series have drivers that
operate at a typical data rate of 250kbps fully
loaded.
The SP3222B and SP3232B are 2-driver/2-
receiver devices ideal for portable or hand-held
applications. The SP3222B 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 SP3222B/3232B 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 can guarantee a data rate of 250kbps
fully loaded with 3KΩ in parallel with 1000pF,
ensuring compatibility with PC-to-PC commu-
nication 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,
Paragraph 5). The transition of the loaded
output from HIGH to LOW also meets the
monotonicity requirements of the standard.
Figure 10 shows a loopback test circuit used to
the RS-232 drivers. Figure 11 shows the test
results of the loopback circuit with all drivers
active at 120kbps with RS-232 loads in parallel
with 1000pF capacitors. Figure 12 shows the
test results where one driver was active at
250kbps and all drivers loaded with an RS-232
receiver in parallel with a 1000pF capacitor. A
solid RS-232 data transmission rate of 250kbps
provides compatibility with many designs in
personal computer peripherals and LAN appli-
cations.
The SP3222B driver's output stages are turned
off (tri-state) when the device is in shutdown
mode. When the power is off, the SP3222B
device permits the outputs to be driven up to
±12V. The driver's inputs do not have pull-up
resistors. Designers should connect unused in-
puts to V_CC or GND.
In the shutdown mode, the supply current falls
to less than 1µA, where SHDN = LOW. When
the SP3222B 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 and V- pulled to GND. The time
CC
required to exit shutdown is typically 100µs.
Connect SHDN to V_CC if the shutdown mode is
not used.
Rev. 6/30/03
SP3222B/3232B True +3.0 to +5.5V RS-232 Transceivers
8
© Copyright 2003 Sipex Corporation