_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3222E/MAX3232E/MAX3237E/MAX3241E’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), 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 con-
vert TTL/CMOS-logic levels to ±5.0V EIA/TIA-232-com-
pliant levels.
The MAX3222E/MAX3232E/MAX3237E/MAX3241E
transmitters guarantee a 250kbps data rate with worst-
case loads of 3k
in parallel with 1000pF, providing
compatibility with PC-to-PC communication software
(such as LapLink). Transmitters can be paralleled to
drive multiple receivers or mice.
The MAX3222E/MAX3237E/MAX3241E’s transmitters are
disabled and the outputs are forced into a high-imped-
ance state when the device is in shutdown mode (
SHDN
=
GND). The MAX3222E/MAX3232E/MAX3237E/MAX3241E
permit the outputs to be driven up to ±12V in shutdown.
The MAX3222E/MAX3232E/MAX3241E transmitter
inputs do not have pull-up resistors. Connect unused
inputs to GND or VCC. The MAX3237E transmitter
inputs have a 400k
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
guarantee a 1Mbps data rate with worst-case loads of
3k
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 3k
in parallel
with 1000pF.
RS-232 Receivers
The receivers convert RS-232 signals to CMOS-logic
output levels. The MAX3222E/MAX3237E/MAX3241E
receivers have inverting three-state outputs. Drive
EN
high to place the receiver(s) into a high-impedance
state. Receivers can be either active or inactive in shut-
down (Table 1).
M
±15kV ESD-Protected, Down to 10nA, 3.0V to 5.5V,
Up to 1Mbps, True RS-232 Transceivers
_______________________________________________________________________________________
7
_________________________________________________Pin Description (continued)
No Connection
N.C.
—
MegaBaud Control Input. Connect to
GND for normal operation; connect to
V
CC
for 1Mbps transmission rates.
Noninverting Complementary
Receiver Outputs. Always active.
MBAUD
15*
R_OUTB
16
Shutdown Control. Active low.
SHDN
14*
+3.0V to +5.5V Supply Voltage
V
CC
26
FUNCTION
NAME
MAX3237E
11, 14
—
—
—
—
—
20
18
19
17
TSSOP/
SSOP
SO/DIP
MAX3222E
1, 10, 11,
20
—
—
—
—
—
—
—
19
16
TSSOP/
SSOP
SO/DIP
MAX3232E
—
—
20, 21
22
26
PIN
MAX3241E
*
These pins have an active positive feedback resistor internal to the MAX3237E, allowing unused inputs to be left unconnected.
LapLink is a trademark of Traveling Software.