SP3221E Datasheet, PDF (8/20 Pages) Sipex Corporation – Intelligent +3.0V to +5.5V RS-232 Transceiver

DESCRIPTION
The SP3221E is a 1-driver/1-receiver device
ideal for portable or handheld applications.
The SP3221E transceiver meets the EIA/
TIA-232 and ITU-T V.28/V.24 communication
protocols and can be implemented in battery-
powered, portable, or handheld applications
such as notebook or handheld computers.
The SP3221E device features the Exar
proprietary and patented (U.S.‑‑ 5,306,954)
on-board charge pump circuitry that gener-
ates ±5.5V RS-232 voltage levels from a
single +3.0V to +5.5V power supply.
This device is an ideal choice for power sen-
sitive designs. Featuring AUTO ON-LINE^®
circuitry, the SP3221E reduces the power
supply drain to a 1µA supply current. In
many portable or handheld applications,
an RS-232 cable can be disconnected or
a connected peripheral can be turned off.
Under these conditions, the internal charge
pump and the drivers will be shut down.
Otherwise, the system automatically comes
online. This feature allows design engineers
to address power saving concerns without
major design changes.
+
C5 0.1µF
2 _C1+
+
C1 0.1µF
4 C1-
5 C2+
+
C2 0.1µF
6 C2-
VCC
15
VCC
SP3221E
V+ ³
V- ⁷
+
C3 0.1µF
C4 0.1µF
+
TTL/CMOS INPUT 11 T1IN
T₁OUT 13
RS-232
OUTPUT
UART
or
Serial µC
TTL/CMOS OUTPUT 9 R1OUT
R₁IN ₈
5KΩ
RS-232
INPUT
RESET
µP
Supervisor
V_IN
IC
1 _EN
VCC
16 _SHUTDOWN
12 _ONLINE
10 _STATUS
GND
14
THEORY OF OPERATION
The SP3221E is made up of four basic
circuit blocks:
1. Driver, 2. Receiver, 3. The Exar propri-
etary charge pump, and 4. AUTO ON-LINE^®
circuitry.
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 +5.4V
with no load and +5V minimum fully loaded.
The driver output is protected against infinite
short-circuits to ground without degradation
in reliability. This driver will comply with
the EIA-TIA-232F and all previous RS-232
versions. Unused driver inputs should be
connected to GND or V_CC.
The driver can guarantee an output data rate
of 250kbps while being 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, Paragraph 5). The transition of the
loaded output from HIGH to LOW also
meets the monotonicity requirements of
the standard.
Figure 6 shows a loopback test circuit used
to test the RS-232 Driver. Figure 8 shows
the test results where the driver was active at
250kbps and loaded with an RS-232 receiver
in parallel with a 1000pF capacitor. RS-232
data transmission rate of 250kbps provides
compatibility with designs in personal com-
puter peripherals and LAN applications.
Figure 5. Interface Circuitry Controlled by Micropro-
cessor Supervisory Circuit
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • [phone] • www.exar.com

SP3221E_102_091014