3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232
Transceivers Using Four 0.1µF External Capacitors
_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3222/MAX3232/MAX3237/MAX3241’s internal
power supply consists of a regulated dual charge pump
that provides output voltages of +5.5V (doubling charge
pump) and -5.5V (inverting charge pump), regardless of
the input voltage (V
CC
) over the 3.0V to 5.5V range. The
charge pumps operate in a discontinuous mode; if the
output voltages are less than 5.5V, the charge pumps
are enabled, and if the output voltages exceed 5.5V, the
charge pumps are disabled. Each charge pump
requires a flying capacitor (C1, C2) and a reservoir
capacitor (C3, C4) to generate the V+ and V- supplies.
The MAX3222/MAX3237/MAX3241’s output stage is
turned off (high impedance) when the device is in shut-
down mode. When the power is off, the MAX3222/
MAX3232/MAX3237/MAX3241 permit the outputs to be
driven up to ±12V.
The transmitter inputs do not have pull-up resistors.
Connect unused inputs to GND or V
CC
.
MAX3222/MAX3232/MAX3237/MAX3241
MAX3237 MegaBaud Operation
In normal operating mode (MBAUD = GND), the
MAX3237 transmitters guarantee a 250kbps data rate
with worst-case loads of 3kΩ in parallel with 1000pF.
This provides compatibility with PC-to-PC communica-
tion software, such as Laplink™.
For higher speed serial communications, the MAX3237
features MegaBaud operation. In MegaBaud operating
mode (MBAUD = V
CC
), the MAX3237 transmitters guar-
antee a 1Mbps data rate with worst-case loads of 3kΩ in
parallel with 250pF for 3.0V < V
CC
< 4.5V. For 5V ±10%
operation, the MAX3237 transmitters guarantee a 1Mbps
data rate into worst-case loads of 3kΩ in parallel with
1000pF.
RS-232 Transmitters
The transmitters are inverting level translators that con-
vert CMOS-logic levels to 5.0V EIA/TIA-232 levels.
The MAX3222/MAX3232/MAX3241 transmitters guaran-
tee a 120kbps data rate with worst-case loads of 3kΩ in
parallel with 1000pF, providing compatibility with PC-to-
PC communication software (such as LapLink™).
Typically, these three devices can operate at data rates
of 235kbps. Transmitters can be paralleled to drive multi-
ple receivers or mice.
LapLink is a trademark of Traveling Software.
V
CC
0.1µF
V
CC
V
CC
0.1µF
V
CC
C1+
C1
C1-
C2+
C2
C2-
T_ IN
V+
C3
C1
C1+
C1-
V+
C3
MAX3222
MAX3232
MAX3237
MAX3241
V-
C4
T_ OUT
C2
C2+
C2-
T_ IN
MAX3222
MAX3232
MAX3237
MAX3241
V-
C4
T_ OUT
R_ OUT
0V
V
CC
EN
*
5k
SHDN
*
GND
R_ IN
0V
V
CC
R_ OUT
EN
*
5k
SHDN
*
GND
R_ IN
3k
2500pF
7k
150pF
*
MAX3222/MAX3241 ONLY
MINIMUM SLEW-RATE TEST CIRCUIT
MAXIMUM SLEW-RATE TEST CIRCUIT
Figure 1. Slew-Rate Test Circuits
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7
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
