MAX3241E MAXIM [Maxim Integrated Products], MAX3241E Datasheet - Page 11

• Manufacturer Part Number: MAX3241E
• Manufacturer: MAXIM [Maxim Integrated Products]

±15kV ESD-Protected, Down to 10nA, 3.0V to 5.5V,
Table 2. Required Minimum Capacitor
Values
___________Applications Information
The capacitor type used for C1–C4 is not critical for
proper operation; polarized or nonpolarized capacitors
can be used. The charge pump requires 0.1µF capaci-
tors for 3.3V operation. For other supply voltages, see
Table 2 for required capacitor values. Do not use val-
ues smaller than those listed in Table 2. Increasing the
capacitor values (e.g., by a factor of 2) reduces ripple
on the transmitter outputs and slightly reduces power
consumption. C2, C3, and C4 can be increased without
changing C1’s value. However, do not increase C1
without also increasing the values of C2, C3, C4,
and C
the other capacitors).
When using the minimum required capacitor values,
make sure the capacitor value does not degrade
excessively with temperature. If in doubt, use capaci-
tors with a larger nominal value. The capacitor’s equiv-
alent series resistance (ESR), which usually rises at low
temperatures, influences the amount of ripple on V+
and V-.
In most circumstances, a 0.1µF V
is adequate. In applications that are sensitive to power-
supply noise, use a capacitor of the same value as
charge-pump capacitor C1. Connect bypass capaci-
tors as close to the IC as possible.
Transmitter outputs will meet EIA/TIA-562 levels of
±3.7V with supply voltages as low as 2.7V.
MAX3222E/MAX3232E/MAX3241E
MAX3237E
3.15 to 3.6
3.0 to 3.6
4.5 to 5.5
3.0 to 5.5
3.0 to 3.6
4.5 to 5.5
3.0 to 5.5
V
BYPASS
(V)
CC
to maintain the proper ratios (C1 to
______________________________________________________________________________________
0.047
0.047
Power-Supply Decoupling
0.22
0.22
(µF)
0.1
0.1
0.1
C1
Operation Down to 2.7V
Up to 1Mbps, True RS-232 Transceivers
Capacitor Selection
CC
bypass capacitor
C2, C3, C4
(µF)
0.33
0.47
0.22
0.33
0.1
0.1
1.0
Figure 3 shows two transmitter outputs when recover-
ing from shutdown mode. As they become active, the
two transmitter outputs are shown going to opposite
RS-232 levels (one transmitter input is high, the other is
low). 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.
The MAX3241E has been specifically designed to
power serial mice while operating from low-voltage
power supplies. It has been tested with leading mouse
brands from manufacturers such as Microsoft and
Logitech. The MAX3241E successfully drove all serial
mice tested and met their respective current and volt-
age requirements. Figure 6a shows the transmitter out-
put voltages under increasing load current at 3.0V.
Figure 6b shows a typical mouse connection using the
MAX3241E.
The MAX3222E/MAX3232E/MAX3237E/MAX3241E
maintain the RS-232 ±5.0V minimum transmitter output
voltage even at high data rates. Figure 7 shows a trans-
mitter loopback test circuit. Figure 8 shows a loopback
test result at 120kbps, and Figure 9 shows the same test
at 250kbps. For Figure 8, all transmitters were driven
simultaneously at 120kbps into RS-232 loads in parallel
with 1000pF. For Figure 9, a single transmitter was driv-
en at 250kbps, and all transmitters were loaded with an
RS-232 receiver in parallel with 1000pF.
Figure 6a. MAX3241E Transmitter Output Voltage vs. Load
Current per Transmitter
-1
-2
-3
-4
-5
-6
6
5
4
3
2
1
0
0
V
V
CC
CC
LOAD CURRENT PER TRANSMITTER (mA)
1
= 3.0V
2
Recovering from Shutdown
Transmitter Outputs when
3
4
5
Mouse Driveability
6
V
V
OUT+
OUT-
High Data Rates
7
8
V
V
OUT+
OUT-
9
10
11