+5V, 1µA, Single RS-232 Transceiver

with AutoShutdown

6

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Table 1. Output Control Truth Table

1

No

Shutdown

(AutoShutdown)

High-Z

1

High-Z

0

1

1

1

OPERATION

STATUS

X

0

VALID

RECEIVER

LEVEL

EN

X

Shutdown

(Forced Off)

X

Normal Operation

(Forced On)

X

0

Yes

Normal Operation

(AutoShutdown)

No

Yes

0

0

High-Z

Active

Active

High-Z

TOUT

Active

High-Z

Active

0

FORCEOFF

1

0

1

1

1

1

High-Z

High-Z

Active

Active

ROUT

High-Z

Active

Active

X

FORCEON

1

X

1

0

0

0

X = Don’t care

RS-232 SIGNAL PRESENT

AT RECEIVER INPUT

INVALID OUTPUT

Yes

High

No

Low

Table 2. INVALID Truth Table

+0.3V

-0.3V

INVALID

TO MAX221

POWER SUPPLY

AND TRANSMITTER

RIN

* TRANSMITTER IS DISABLED, REDUCING SUPPLY CURRENT TO 1

µA IF

RECEIVER INPUT IS BETWEEN +0.3V AND -0.3V FOR AT LEAST 30

µs.

30

µs

COUNTER

R

+2.7V

-2.7V

INVALID

TO MAX221

POWER SUPPLY

RIN

* TRANSMITTER IS ENABLED IF:

RECEIVER INPUT IS GREATER THAN +2.7V OR LESS THAN -2.7V;

RECEIVER INPUT HAS BEEN BETWEEN +0.3V AND -0.3V FOR LESS THAN 30

µs.

30µs

COUNTER

R

Figure 2b. Transmitter Enabled Using AutoShutdown

Figure 2a. Entering 1µA Supply Mode via AutoShutdown

FORCEOFF

POWER DOWN

INVALID

FORCEON

INVALID IS AN INTERNALLY GENERATED SIGNAL USED BY

THE AUTOSHUTDOWN LOGIC AND APPEARS AS AN OUTPUT.

POWER DOWN IS ONLY AN INTERNAL SIGNAL. IT CONTROLS THE

OPERATIONAL STATUS OF THE TRANSMITTER AND POWER SUPPLIES.

Figure 2c. AutoShutdown Logic