1µA Supply-Current, True +3V to +5.5V

RS-232 Transceivers with AutoShutdown

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5

______________________________________________________________Pin Description

Noninverting Receiver Output—active in shutdown

R2OUTB

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

ent on receiver inputs logic “1”.

INVALID

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

rides all automatic circuitry and FORCEON (Table 1).

FORCEOFF

Drive high to override automatic circuitry keeping transmitters on

(FORCEOFF must be high) (Table 1).

FORCEON

Negative terminal of the voltage doubler charge-pump capacitor

C1-

RS-232 Receiver Inputs

R_IN

RS-232 Transmitter Outputs

T_OUT

TTL/CMOS Transmitter Inputs

T_IN

TTL/CMOS Receiver Outputs

R_OUT

-5.5V generated by the charge pump

V-

Negative terminal of inverting charge-pump capacitor

C2-

Positive terminal of inverting charge-pump capacitor

C2+

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

the receiver outputs into a high-Z state.

EN

FUNCTION

Ground

GND

+3.0V to +5.5V Supply Voltage

LapLink is a trademark of Traveling Software.

_______________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

range. The charge 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 con-

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

guarantee 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, the MAX3221/MAX3223/MAX3243 can oper-

ate at data rates of 235kbps. Transmitters can be paral-

leled to drive multiple receivers or mice (MAX3243).

Figure 1 shows a complete system connection.

When FORCEOFF is driven to ground, or the Auto-

Shutdown circuitry senses invalid voltage levels at all

receiver inputs, the transmitters are disabled and the

outputs are forced into a high-impedance state.

—

10

16

12

4

8

13

11

9

7

6

5

1

14

15

NAME

MAX3221

+5.5V generated by the charge pump

V+

3

Positive terminal of the voltage doubler charge-pump capacitor

C1+

2

—

11

20

14

4

9, 16

8, 17

12, 13

10, 15

7

6

5

1

18

19

20

21

22

23

24

4–8

9, 10, 11

12, 13, 14

15–19

3

2

1

—

25

26

MAX3223

3

MAX3243

27

2

28

PIN