Detailed Description

Dual Charge-Pump Voltage Converter

The MAX3221/MAX3223/MAX3243’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

pumps operate in a discontinuous mode: if the output

voltages are less than 5.5V, the charge pumps are

enabled; 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

convert CMOS-logic levels to 5.0V EIA/TIA-232 levels.

They guarantee 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, the MAX3221/MAX3223/MAX3243 can operate

at data rates of 235kbps. Transmitters can be paralleled

to drive multiple receivers or mice (MAX3243). Figure 1

shows a complete system connection.

When FORCEOFF is driven to ground, or the auto-shut-

down circuitry senses invalid voltage levels at all receiver

inputs, the transmitters are disabled and the outputs are

forced into a high-impedance state.

LapLink is a trademark of Traveling Software.

PIN

NAME

FUNCTION

MAX3221

MAX3223

MAX3243

1

1

—

EN

Receiver Enable Control. Drive low for normal operation. Drive high to

force the receiver outputs into a high-Z state.

5

5

1

C2+

Positive terminal of inverting charge-pump capacitor

6

6

2

C2-

Negative terminal of inverting charge-pump capacitor

7

7

3

V-

-5.5V generated by the charge pump

8

9, 16

4–8

R_IN

RS-232 Receiver Inputs

13

8, 17

9, 10, 11

T_OUT

RS-232 Transmitter Outputs

11

12, 13

12, 13, 14

T_IN

TTL/CMOS Transmitter Inputs

9

10, 15

15–19

R_OUT

TTL/CMOS Receiver Outputs

—

—

20

R2OUTB

Noninverting Receiver Output—active in shutdown

10

11

21

INVALID

Output of the valid signal detector. Indicates if a valid RS-232 level is

present on receiver inputs logic “1”.

16

20

22

FORCEOFF

Drive low to shut down transmitters and on-board power supply.

This overrides all automatic circuitry and FORCEON (Table 1).

12

14

23

FORCEON

Drive high to override automatic circuitry keeping transmitters on

(FORCEOFF must be high) (Table 1).

4

4

24

C1-

Negative terminal of the voltage doubler charge-pump capacitor

14

18

25

GND

Ground

15

19

26

+3.0V to +5.5V Supply Voltage

3

3

27

V+

+5.5V generated by the charge pump

2

2

28

C1+

Positive terminal of the voltage doubler charge-pump capacitor

Pin Description

MAX3221/MAX3223/

MAX3243

+3V to +5.5V RS-232

Transceivers with AutoShutdown

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