Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com SP3220E_EB_EU_102_102016
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The SP3220E/EB/EU devices meet the
EIA/TIA-232 and ITU-T V.28/V.24 commu-
nication protocols and can be implemented
in battery-powered, portable, or hand-held
applications such as notebook or palmtop
computers. The SP3220E/EB/EU devices
feature Exar's proprietary on-board charge
pump circuitry that generates ±5.5V 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 SP3220EB
device has a driver that can operate at a data
rate of 250kbps fully loaded. The SP3220EU
can operate at 1000kbps; the SP3220E
device can operate at a typical data rate of
235kbps when fully loaded.
The SP3220E/EB/EU is a 1-driver/1- receiver
device ideal for portable or hand-held ap-
plications. The SP3220E/EB/EU features a
1µA shutdown mode that reduces power
consumption and extends battery life in por-
table 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 SP3220E/EB/EU series is made up of
three basic circuit blocks:
1. Driver
2. Receiver
3. The Exar proprietary charge pump
Driver
The driver is an inverting level transmitter that
converts TTL or CMOS logic levels to +5.0V
EIA/TIA-232 levels with an inverted sense
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 innite short-circuits to ground with-
out degradation in reliability. Driver outputs
will meet EIA/TIA-562 levels of +/-3.7V with
supply voltages as low as 2.7V.
The SP3220EB driver can guarantee a data
rate of 250kbps fully loaded with 3kΩ in
parallel with 1000pF, ensuring compatibility
with PC-to-PC communication software. The
SP3220EU driver can guarantee a data rate
of 1000kbps fully loaded with 3kΩ in parallel
with 250pF.
The slew rate of the SP3220E and
SP3220EB outputs are 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 meet the monotonicity
requirements of the standard. The slew rate
of the SP3220EU is not limited. This allows
it to transmit at much faster data rates.
Figure 12 shows a loopback test circuit
used to test the RS-232 Driver. Figure
13 shows the test results of the loopback
circuit with the SP3220EB driver active at
250kbps with RS-232 load in parallel with
a 1000pF capacitor. Figure 14 shows the
test results where the SP3220EU driver
was active at 1000kbps and loaded with an
RS-232 receiver in parallel with 250pF ca-
pacitors. A solid RS-232 data transmission
rate of 250kbps provides compatibility with
many designs in personal computer periph-
erals and LAN applications.
The SP3220E/EB/EU driver's output stage
is turned o (tri-state) when the device
is in shutdown mode. When the power is
o, the SP3220E/EB/EU 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
Vcc or GND.
In the shutdown mode, the supply current
falls to less than 1µA, where SHDN = LOW.
When the SP3220E/EB/EU device is shut
down, the device's driver output is disabled
DESCRIPTION
