DESCRIPTION
The SP3243E transceivers meet the EIA/TIA-
232 and ITU-T 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 SP3243E
devices feature Exar's proprietary and patented
(U.S.-- 5,306,954) on-board charge pump cir-
cuitry that generates ±5.5V RS-232 voltage levels
from a single +3.0V to +5.5V power supply. The
SP3243EU devices can operate at a data rate
of 1000kbps fully loaded.
The SP3243E is a 3-driver/5-receiver device,
ideal for portable or hand-held applications.
The SP3243E includes one complementary
always-active receiver that can monitor an
external device (such as a modem) in shutdown.
This aids in protecting the UART or serial
controller IC by preventing forward biasing
of the protection diodes where V
CC
may be
disconnected.
In many portable or hand-held applications, an
RS-232 cable can be disconnected or a connected
peripheral can be turned off. Under these condi-
tions, the internal charge pump and the drivers will
be shut down. Otherwise, the system automati-
cally comes online. This feature allows design
engineers to address power saving concerns
without major design changes.
THEORY OF OPERATION
The SP3243E series is made up of four basic
circuit blocks:
1. Drivers
2. Receivers
3. the Exar proprietary charge pump, and
4. AUTO ON-LINE
®
circuitry.
Drivers
The drivers are inverting level transmitters that
convert 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 outputs are
protected against infinite short-circuits to ground
without degradation in reliability. These drivers
comply with the EIA-TIA-232-F and all previous
RS-232 versions. Unused drivers inputs should
be connected to GND or V
CC
.
The drivers have a minimum data rate of 250kbps
(EB) or 1000kbps (EU) fully loaded.
The SP3243E series is an ideal choice for power
sensitive designs. The SP3243E devices feature
AUTO ON-LINE
®
circuitry which reduces the
power supply drain to a 1µA supply current.
V
CC
C5
C1
+
+
0.1 µF
28 C1+
0.1 µF
24 C1-
1 C2+
0.1 µF
2 C2-
14
T
1
IN
13
T
2
IN
12
T
3
IN
20
R
2
OUT
T
1
OUT
26
V
CC
V+
27
C3
3
C4
9
+
0.1 µF
C2
+
SP3243E
V-
+
0.1 µF
TxD
RTS
DTR
T
2
OUT
10
T
3
OUT
11
RS-232
OUTPUTS
UART
or
Serial µC
RxD
CTS
DSR
DCD
RI
V
CC
19
R
1
OUT
18
R
2
OUT
17
R
3
OUT
16
R
4
OUT
15
R
5
OUT
22
23
21
SHUTDOWN
ONLINE
STATUS
R
1
IN
4
5KΩ
5KΩ
5KΩ
5KΩ
5KΩ
R
2
IN
R
3
IN
R
4
IN
R
5
IN
5
6
7
8
RS-232
INPUTS
GND
25
Figure 11 shows a loopback test circuit used to
test the RS-232 Drivers. Figure 12 shows the
test results where one driver was active at 1Mbps
and all three drivers loaded with an RS-232 re-
ceiver in parallel with a 250pF capacitor. Figure
13 shows the test results of the loopback circuit
with all drivers active at 250kbps with typical
RS-232 loads in parallel with 1000pF capacitors. A
superior RS-232 data transmission rate of 1Mbps
makes the SP3243EU an ideal match for high
speed LAN and personal computer peripheral
applications.
RESET
µP
Supervisor
IC
VIN
Figure 10. Interface Circuitry Controlled by Micropro-
cessor Supervisory Circuit
Exar Corporation 48720 Kato Road, Fremont CA, 94538 • 510-668-7017 • www.exar.com
SP3243E_100_072309
8
EXAR [ EXAR CORPORATION ]
