Datasheet

Power-Supply Decoupling
In most circumstances a 0.1µF bypass capacitor is adequate.
In applications that are sensitive to power-supply noise,
decouple V
CC
to ground with a capacitor of the same
value as the charge-pump capacitor C1. Connect bypass
capacitors as close to the IC as possible.
Transmitter Outputs
when Exiting Shutdown
Figure 6 shows two transmitter outputs when exiting
shutdown mode. As they become active, the two trans-
mitter outputs are shown going to opposite RS-232
levels. Each transmitter is loaded with 3kΩ in parallel
with 2500pF. The transmitter outputs display no ringing
or undesirable transients as they come out of shutdown.
Note that the transmitters are enabled only when the
magnitude of V- exceeds approximately 3V. Figure 7a
shows the MAX3243’s transmitter output voltage vs.
current per transmitter. Figure 7b is a mouse driver test
circuit.
Mouse Driveability (MAX3243)
The MAX3243 has been specifically designed to power
serial mice while operating from low-voltage power
supplies. It has been tested with samples of ten major
mouse models from six manufacturers including the
leading three: Logitech (5 models), Mouse Systems,
and Microsoft. The MAX3243 successfully drove all
serial mice and met their respective current and voltage
requirements. Figure 7a shows the transmitter outputs
under increasing load current. The MAX3243’s switching
regulator ensures the transmitters will supply at least
±5V during worst-case conditions. The AutoShutdown
feature does not work with a mouse, so FORCEOFF and
FORCEON should be connected to V
CC
.
High Data Rates
The MAX3221/MAX3223/MAX3243 maintain the RS-232
±5.0V minimum transmitter output voltage even at high
data rates. Figure 8 shows a transmitter loopback test
circuit. Figure 9 shows a loopback test result at 120kbps,
and Figure 10 shows the same test at 235kbps. For
Figure 9, all three transmitters were driv-en simultaneously
at 120kbps into RS-232 loads in parallel with 1000pF. For
Figure 10, a single transmitter was driven at 235kbps,
but all three transmitters were loaded with an RS-232
receiver in parallel with 1000pF.
Interconnection with
3V and 5V Logic
The MAX3221/MAX3223/MAX3243 can directly interface
with various 5V logic families, including ACT and HCT
CMOS. See Table 4 for more information on possible
combinations of interconnections.
Figure 6. Transmitter Outputs When Exiting Shutdown or
Powering Up
Figure 7a. MAX3243 Transmitter Output Voltage vs. Load
Current per Transmitter
5V/div
V
CC
= +3.3V
C1–C4 = 0.1µF
2V/div
T2
50µs/div
T1
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
0 1 2 3 4 5 6 7
MAX3222-04
LOAD CURRENT PER TRANSMITTER (mA)
TRANSMITTER OUTPUT VOLTAGE (V)
V
OUT
+
V
CC
= 3.0V
V
OUT
-
V
OUT
+
V
CC
V
OUT
-
T
1
T
2
T
3
MAX3221/MAX3223/
MAX3243
+3V to +5.5V RS-232
Transceivers with AutoShutdown
www.maximintegrated.com
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