MAX3243EWI+ Maxim Integrated Products, MAX3243EWI+ Datasheet - Page 9

• Manufacturer Part Number: MAX3243EWI+
• Description: IC TXRX RS-232 W/SHTDWN 28-SOIC
• Manufacturer: Maxim Integrated Products
• Type: Transceiverr

Specifications of MAX3243EWI+

• Number Of Drivers/receivers: 3/5
• Protocol: RS232
• Voltage - Supply: 3 V ~ 5.5 V
• Mounting Type: Surface Mount
• Package / Case: 28-SOIC (7.5mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

In most circumstances a 0.1µF bypass capacitor is
adequate. In applications that are sensitive to power-
supply noise, decouple V
of the same value as the charge-pump capacitor C1.
Connect bypass capacitors as close to the IC as possible.
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 shut-
down. 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.
The MAX3243 has been specifically designed to power
serial mice while operating from low-voltage power sup-
plies. It has been tested with samples of ten major mouse
models from six manufacturers including the leading
three: Logitech (5 models), Mouse Systems, and
Figure 6. Transmitter Outputs when Exiting Shutdown or
Powering Up
5V/div
2V/div
V
C1–C4 = 0.1µF
CC
= +3.3V
RS-232 Transceivers with AutoShutdown
Mouse Driveability (MAX3243)
_______________________________________________________________________________________
Power-Supply Decoupling
1µA Supply-Current, True +3V to +5.5V
when Exiting Shutdown
CC
50µs/div
Transmitter Outputs
to ground with a capacitor
T2
T1
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
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 par-
allel 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.
The MAX3221/MAX3223/MAX3243 can directly inter-
face with various 5V logic families, including ACT and
HCT CMOS. See Table 4 for more information on possi-
ble combinations of interconnections.
Figure 7a. MAX3243 Transmitter Output Voltage vs. Load
Current per Transmitter
Interconnection with 3V and 5V Logic
-1
-2
-3
-4
-5
-6
6
5
4
3
2
1
0
0
LOAD CURRENT PER TRANSMITTER (mA)
V
V
CC
CC
1
= 3.0V
T
T
T
1
2
3
2
3
V
V
OUT
OUT
4
+
-
High Data Rates
5
CC .
V
V
OUT
OUT
6
+
-
7
9