±15kV ESD-Protected, Down to 10nA, 3.0V to 5.5V,

Up to 1Mbps, True RS-232 Transceivers

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Detailed Description

Dual Charge-Pump Voltage Converter

The MAX3222E/MAX3232E/MAX3237E/MAX3241E/

MAX3246Es’ 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 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 ±5V EIA/TIA-232-compli-

ant levels.

The MAX3222E/MAX3232E/MAX3237E/MAX3241E/

MAX3246E transmitters guarantee a 250kbps data rate

with worst-case loads of 3k

Ω in parallel with 1000pF,

providing compatibility with PC-to-PC communication

software (such as LapLink™). Transmitters can be par-

alleled 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 shut-

down 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

mitter inputs have a 400k

Ω 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

MAX3237E transmitters guarantee a 1Mbps data rate

with worst-case loads of 3k

Ω in parallel with 250pF for

MAX3237E transmitters guarantee a 1Mbps data rate

into worst-case loads of 3k

Ω 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-

impedance state. Receivers can be either active or

inactive in shutdown (Table 1).

MAX3222E

MAX3232E

MAX3237E

MAX3241E

MAX3246E

5k

Ω

R_ IN

R_ OUT

C2-

C2+

C1-

C1+

V-

V+

C4

C3

C1

C2

0.1

µF

T_ OUT

T_ IN

GND

7k

Ω

150pF

MAX3222E

MAX3232E

MAX3237E

MAX3241E

MAX3246E

5k

Ω

R_ IN

R_ OUT

C2-

C2+

C1-

C1+

V-

V+

C4

C3

C1

C2

0.1

µF

T_ OUT

T_ IN

GND

3k

Ω

1000pF

(2500pF, MAX3237E only)

MINIMUM SLEW-RATE TEST CIRCUIT

MAXIMUM SLEW-RATE TEST CIRCUIT

Figure 1. Slew-Rate Test Circuits

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