Datasheet

Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3222E/MAX3232E/MAX3237E/MAX3241E/
MAX3246E’s internal power supply consists of a regu-
lated dual charge pump that provides output voltages
of +5.5V (doubling charge pump) and -5.5V (inverting
charge pump) over the +3.0V to +5.5V V
CC
range. The
charge pump operates in discontinuous mode; if the
output voltages are less than 5.5V, the charge pump
is enabled, and if the output voltages exceed 5.5V, the
charge pump is disabled. Each charge pump requires a
flying capacitor (C1, C2) and a reservoir capacitor (C3,
C4) to generate the V+ and V- supplies (Figure 1).
RS-232 Transmitters
The transmitters are inverting level translators that convert
TTL/CMOS-logic levels to ±5V EIA/TIA-232-compliant
levels.
The MAX3222E/MAX3232E/MAX3237E/MAX3241E/
MAX3246E transmitters guarantee a 250kbps data rate
with worst-case loads of 3kΩ in parallel with 1000pF,
providing compatibility with PC-to-PC communication
software (such as LapLink™). Transmitters can be paral-
leled to drive multiple receivers or mice.
The MAX3222E/MAX3237E/MAX3241E/MAX3246E
transmitters are disabled and the outputs are forced into
a high-impedance state when the device is in shutdown
mode (SHDN = GND). The MAX3222E/MAX3232E/
MAX3237E/MAX3241E/MAX3246E permit the outputs to
be driven up to ±12V in shutdown.
The MAX3222E/MAX3232E/MAX3241E/MAX3246E
transmitter inputs do not have pullup resistors. Connect
unused inputs to GND or V
CC
. The MAX3237E’s transmit-
ter inputs have a 400kΩ active positive-feedback resistor,
allowing unused inputs to be left unconnected.
MAX3237E MegaBaud Operation
For higher-speed serial communications, the MAX3237E
features MegaBaud operation. In MegaBaud operating
mode (MBAUD = V
CC
), the MAX3237E 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 MAX3237E transmitters guarantee a
1Mbps data rate into worst-case loads of 3kΩ in parallel
with 1000pF.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels. The MAX3222E/MAX3237E/MAX3241E/
MAX3246E receivers have inverting three-state outputs.
Drive EN high to place the receiver(s) into a high-imped-
ance state. Receivers can be either active or inactive in
shutdown (Table 1).
Figure 1. Slew-Rate Test Circuits
LapLink is a trademark of Traveling Software.
MAX3222E
MAX3232E
MAX3237E
MAX3241E
MAX3246E
5kΩ
R_ IN
R_ OUT
C2-
C2+
C1-
C1+
V-
V+
V
CC
C4
C3
C1
C2
0.1µF
V
CC
T_ OUT
T_ IN
GND
7kΩ
150pF
MAX3222E
MAX3232E
MAX3237E
MAX3241E
MAX3246E
5kΩ
R_ IN
R_ OUT
C2-
C2+
C1-
C1+
V-
V+
V
CC
C4
C3
C1
C2
0.1µF
V
CC
T_ OUT
T_ IN
GND
3kΩ
1000pF
(2500pF, MAX3237E only)
MINIMUM SLEW-RATE TEST CIRCUIT MAXIMUM SLEW-RATE TEST CIRCUIT
www.maximintegrated.com
Maxim Integrated │ 9
MAX3222E/MAX3232E/
MAX3237E/MAX3241E/
MAX3246E
±15kV ESD-Protected, Down to 10nA,
3.0V to 5.5V, Up to 1Mbps,
True RS-232 Transceivers