SP3220 Datasheet, PDF (8/16 Pages) Sipex Corporation – +3.0V to +5.5V RS-232 Driver/Receiver Pair

DESCRIPTION
The SP3220 device meets the EIA/TIA-232 and
V.28/V.24 communication protocols and can be
implemented in battery-powered,
portable, or hand-held applications such as
notebook or palmtop computers. The SP3220
device features 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 +3.0V to +5.5V
systems, or +5.0V-only systems that require true
RS-232 performance. The SP3220 device has a
driver that operates at a typical data rate of
235Kbps fully loaded.
The SP3220 is a 1-driver/1-receiver device ideal
for portable or hand-held applications. The
SP3220 features a 1µA shutdown mode that
reduces power consumption 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 SP3220 device is 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
input 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 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.
The SP3220 driver can maintain high data rates
up to 235Kbps fully loaded. Figure 6 shows a
loopback test circuit used to test the
RS-232 driver. Figure 7 shows the test results of
the loopback circuit with the driver active at
120Kbps with an RS-232 load in parallel with a
1000pF capacitor. Figure 8 shows the test results
where the driver was active at 235Kbps and
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 SP3220 driver's output stage is turned off
(high-Z) when the device is in shutdown mode.
When the power is off, the SP3220 device
permits the outputs to be driven up to +12V. The
driver's input does not have pull-up resistors.
Designers should connect an unused input
to V_CC or GND.
In the shutdown mode, the supply current falls to
less than 1µA, where SHDN = LOW. When the
SP3220 device is shut down, the device's
driver output is disabled (high-Z) and the charge
pump is 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 not used. SHDN has
CC
no effect on RxOUT. Note that the driver is
enabled only when the magnitude of V- exceeds
approximately 3V.
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.
Rev. 6/25/03
SP3220 True +3.0 to +5.0V RS-232 Transceivers
8
© Copyright 2003 Sipex Corporation