3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232

Transceivers Using Four 0.1µF External Capacitors

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7

_______________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

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.

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 3k

Ω 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.

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.

MAX3237 MegaBaud Operation

In normal operating mode (MBAUD = GND), the

MAX3237 transmitters guarantee a 250kbps data rate

with worst-case loads of 3k

Ω 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

antee a 1Mbps data rate with worst-case loads of 3k

Ω in

operation, the MAX3237 transmitters guarantee a 1Mbps

data rate into worst-case loads of 3k

Ω in parallel with

1000pF.

MAX3222

MAX3232

MAX3237

MAX3241

5k

R_ IN

R_ OUT

EN

*

C2-

C2+

C1-

C1+

V-

V+

C4

C3

C1

C2

0.1

µF

SHDN

*

T_ OUT

T_ IN

GND

0V

7k

150pF

MAX3222

MAX3232

MAX3237

MAX3241

5k

R_ IN

R_ OUT

EN

*

C2-

C2+

C1-

C1+

V-

V+

C4

C3

C1

C2

0.1

µF

SHDN

*

T_ OUT

T_ IN

GND

0V

3k

2500pF

MINIMUM SLEW-RATE TEST CIRCUIT

MAXIMUM SLEW-RATE TEST CIRCUIT

Figure 1. Slew-Rate Test Circuits

LapLink is a trademark of Traveling Software.