±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,
RS-232 Transceivers with AutoShutdown
MAX3221E/MAX3223E/MAX3243E
High Data Rates
The MAX3221E/MAX3223E/MAX3243E maintain the RS-
232 ±5.0V minimum transmitter output voltage even at
high data rates. Figure 9 shows a transmitter loopback
test circuit. Figure 10 shows a loopback test result at
120kbps, and Figure 11 shows the same test at 250kbps.
For Figure 10, all three transmitters were driven simulta-
neously at 120kbps into RS-232 loads in parallel with
1000pF. For Figure 11, a single transmitter was driven at
250kbps, and all three transmitters were loaded with an
RS-232 receiver in parallel with 1000pF.
Mouse Driveability (MAX3243E)
The MAX3243E has been specifically designed to power
serial mice while operating from low-voltage power sup-
plies. It has been tested with leading mouse brands such
as Logitech and Microsoft. When tested, the MAX3243E
successfully drove all serial mice and met their respective
current and voltage requirements. The MAX3243E’s regu-
lated dual charge pump ensures the transmitters will sup-
ply at least ±5V during worst-case conditions. Figure 12a
shows the transmitter outputs under increasing load cur-
rent. The AutoShutdown feature does not work with a
mouse, so
FORCEOFF
and FORCEON should be con-
nected to V
CC
. Figure 12b (on the following page) shows
a mouse driver test circuit. To achieve mouse driveability
with 1µA supply current when the port is inactive, use
parts with the AutoShutdown Plus feature (such as the
MAX3244E and MAX3245E).
V
CC
0.1µF
C1+
C1
C1-
C2+
C2
C2-
T_ IN
R_ OUT
0V
V
CC
EN (MAX3221/3E)
FORCEOFF
V
CC
V+
C3
MAX3221E
MAX3223E
MAX3243E
V-
C4
T1IN
5V/div
T_ OUT
T1OUT
5V/div
R_ IN
5k
1000pF
GND
R1OUT
V
CC
= 3.3V
2µs/div
5V/div
Figure 11. Loopback Test Result at 250kbps
Figure 9. Loopback Test Circuit
6
5
4
3
2
1
0
-1
-2
-3
-4
-5
-6
0
2µs/div
MAX2343E-FIG15
TRANSMITTER OUTPUT VOLTAGE (V)
V
CC
= 3.0V
V
OUT+
V
OUT+
T1IN
5V/div
5V/div
T1OUT
V
CC
V
OUT-
V
OUT-
R1OUT
V
CC
= 3.3V
5V/div
1
2
3
4
5
6
7
8
9
10
LOAD CURRENT PER TRANSMITTER (mA)
Figure 10. Loopback Test Result at 120kbps
12
Figure 12a. Transmitter Output Voltage vs. Load Current per
Transmitter
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